Tag Archives: High Energy Physics – Lattice

First-order phase transitions in Yang-Mills theories and the density of state method [CL]

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http://arxiv.org/abs/2305.07463


When studied at finite temperature, Yang-Mills theories in $3+1$ dimensions display the presence of confinement/deconfinement phase transitions, which are known to be of first order — the $SU(2)$ gauge theory being the exception. Theoretical as well as phenomenological considerations indicate that it is essential to establish a precise characterisation of these physical systems in proximity of such phase transitions. We present and test a new method to study the critical region of parameter space in non-Abelian quantum field theories on the lattice, based upon the Logarithmic Linear Relaxation (LLR) algorithm. We apply this method to the $SU(3)$ Yang Mills lattice gauge theory, and perform extensive calculations with one fixed choice of lattice size. We identify the critical temperature, and measure interesting physical quantities near the transition. Among them, we determine the free energy of the model in the critical region, exposing for the first time its multi-valued nature with a numerical calculation from first principles, providing this novel evidence in support of a first order phase transition. This study sets the stage for future high precision measurements, by demonstrating the potential of the method.

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B. Lucini, D. Mason, M. Piai, et. al.
Mon, 15 May 23
48/53

Comments: 25 pages, 21 figures

Strong-Field Physics in QED and QCD: From Fundamentals to Applications [CL]

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http://arxiv.org/abs/2305.03865


We provide a pedagogical review article on fundamentals and applications of the quantum dynamics in strong electromagnetic fields in QED and QCD. The fundamentals include the basic picture of the Landau quantization and the resummation techniques applied to the class of higher-order diagrams that are enhanced by large magnitudes of the external fields. We then discuss observable effects of the vacuum fluctuations in the presence of the strong fields, which consist of the interdisciplinary research field of nonlinear QED. We also discuss extensions of the Heisenberg-Euler effective theory to finite temperature/density and to non-Abelian theories with some applications. Next, we proceed to the paradigm of the dimensional reduction emerging in the low-energy dynamics in the strong magnetic fields. The mechanisms of superconductivity, the magnetic catalysis of the chiral symmetry breaking, and the Kondo effect are addressed from a unified point of view in terms of the renormalization-group method. We provide an up-to-date summary of the lattice QCD simulations in magnetic fields for the chiral symmetry breaking and the related topics as of the end of 2022. Finally, we discuss novel transport phenomena induced by chiral anomaly and the axial-charge dynamics. Those discussions are supported by a number of appendices.

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K. Hattori, K. Itakura and S. Ozaki
Tue, 9 May 23
53/88

Comments: Prepared for an invited review article

Exploring QCD matter in extreme conditions with Machine Learning [CL]

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http://arxiv.org/abs/2303.15136


In recent years, machine learning has emerged as a powerful computational tool and novel problem-solving perspective for physics, offering new avenues for studying strongly interacting QCD matter properties under extreme conditions. This review article aims to provide an overview of the current state of this intersection of fields, focusing on the application of machine learning to theoretical studies in high energy nuclear physics. It covers diverse aspects, including heavy ion collisions, lattice field theory, and neutron stars, and discuss how machine learning can be used to explore and facilitate the physics goals of understanding QCD matter. The review also provides a commonality overview from a methodology perspective, from data-driven perspective to physics-driven perspective. We conclude by discussing the challenges and future prospects of machine learning applications in high energy nuclear physics, also underscoring the importance of incorporating physics priors into the purely data-driven learning toolbox. This review highlights the critical role of machine learning as a valuable computational paradigm for advancing physics exploration in high energy nuclear physics.

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K. Zhou, L. Wang, L. Pang, et. al.
Tue, 28 Mar 23
59/81

Comments: 146 pages,53 figures

Equation of state and speed of sound of isospin-asymmetric QCD on the lattice [CL]

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http://arxiv.org/abs/2212.14016


We determine the QCD equation of state at nonzero temperature in the presence of an isospin asymmetry between the light quark chemical potentials on the lattice. Our simulations employ $N_f=2+1$ flavors of dynamical staggered quarks at physical masses, using three different lattice spacings. The main results are based on a two-dimensional spline interpolation of the isospin density, from which all relevant quantities can be obtained analytically. In particular, we present results for the pressure, the interaction measure, the energy and entropy densities, as well as the speed of sound. Remarkably, the latter is found to exceed its ideal gas limit deep in the pion condensed phase, the first account of the violation of this limit in first principles QCD. Finally, we also compute the phase diagram in the temperature — isospin density plane for the first time. The data for all observables will be useful for the benchmarking of effective theories and low-energy models of QCD and are provided in ancillary files for simple reuse.

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B. Brandt, F. Cuteri and G. Endrodi
Thu, 29 Dec 22
28/47

Comments: 28 pages, 42 figures

Equation of state and speed of sound of isospin-asymmetric QCD on the lattice [CL]

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http://arxiv.org/abs/2212.14016


We determine the QCD equation of state at nonzero temperature in the presence of an isospin asymmetry between the light quark chemical potentials on the lattice. Our simulations employ $N_f=2+1$ flavors of dynamical staggered quarks at physical masses, using three different lattice spacings. The main results are based on a two-dimensional spline interpolation of the isospin density, from which all relevant quantities can be obtained analytically. In particular, we present results for the pressure, the interaction measure, the energy and entropy densities, as well as the speed of sound. Remarkably, the latter is found to exceed its ideal gas limit deep in the pion condensed phase, the first account of the violation of this limit in first principles QCD. Finally, we also compute the phase diagram in the temperature — isospin density plane for the first time. The data for all observables will be useful for the benchmarking of effective theories and low-energy models of QCD and are provided in ancillary files for simple reuse.

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B. Brandt, F. Cuteri and G. Endrodi
Thu, 29 Dec 22
37/47

Comments: 28 pages, 42 figures

Microcanonical Hamiltonian Monte Carlo [CL]

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http://arxiv.org/abs/2212.08549


We develop Microcanonical Hamiltonian Monte Carlo (MCHMC), a class of models which follow a fixed energy Hamiltonian dynamics, in contrast to Hamiltonian Monte Carlo (HMC), which follows canonical distribution with different energy levels. MCHMC tunes the Hamiltonian function such that the marginal of the uniform distribution on the constant-energy-surface over the momentum variables gives the desired target distribution. We show that MCHMC requires occasional energy conserving billiard-like momentum bounces for ergodicity, analogous to momentum resampling in HMC. We generalize the concept of bounces to a continuous version with partial direction preserving bounces at every step, which gives an energy conserving underdamped Langevin-like dynamics with non-Gaussian noise (MCLMC). MCHMC and MCLMC exhibit favorable scalings with condition number and dimensionality. We develop an efficient hyperparameter tuning scheme that achieves high performance and consistently outperforms NUTS HMC on several standard benchmark problems, in some cases by more than an order of magnitude.

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J. Robnik, G. Luca, E. Silverstein, et. al.
Mon, 19 Dec 22
28/62

Comments: 32 pages, 10 figures

The density of state method for first-order phase transitions in Yang-Mills theories [CL]

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http://arxiv.org/abs/2212.01074


Lattice Field Theory can be used to study finite temperature first-order phase transitions in new, strongly-coupled gauge theories of phenomenological interest. Metastable dynamics arising in proximity of the phase transition can lead to large, uncontrolled numerical errors when analysed with standard methods. In this contribution, we discuss a prototype lattice calculation in which the first-order deconfinement transition in the strong Yang-Mills sector of the standard model is analysed using a novel lattice method, the logarithmic linear relaxation algorithm. This method provides a determination of the density of states of the system with exponential error suppression. Thermodynamic observables can be reconstructed with a controlled error, providing a promising direction for accurate numerical predictions.

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D. Mason, B. Lucini, M. Piai, et. al.
Mon, 5 Dec 22
4/63

Comments: 10 pages, 6 figures; contribution to the proceedings of the 39th Lattice conference, 8th-13th August 2022, Bonn, Germany. arXiv admin note: text overlap with arXiv:2211.10373

Gravitational Waves from dark composite dynamics [CL]

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http://arxiv.org/abs/2211.08877


We discuss the stochastic gravitational-wave spectrum from dark confinement and chiral phase transitions in the early Universe. Specifically, we look at pure Yang-Mills theory for an arbitrary number of colours as well as SU(3) with quarks in different representations. We utilise thermodynamic lattice data and map it to effective models, such as the Polyakov-loop and the PNJL model. This allows us to compute gravitational-wave parameters and the corresponding gravitational-wave signal. We compare the signal to future gravitational-wave observatories such as the Big Bang Observer and DECIGO.

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M. Reichert and Z. Wang
Thu, 17 Nov 22
38/63

Comments: 8 pages, 3 figures, contribution to the proceedings of the XVth Quark Confinement and the Hadron Spectrum conference at the University of Stavanger

Snowmass Theory Frontier Report [CL]

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http://arxiv.org/abs/2211.05772


This report summarizes the recent progress and promising future directions in theoretical high-energy physics (HEP) identified within the Theory Frontier of the 2021 Snowmass Process.

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N. Craig, C. Csáki, A. El-Khadra, et. al.
Fri, 11 Nov 22
23/58

Comments: N/A

Probing nuclear observables via primordial nucleosynthesis [CL]

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http://arxiv.org/abs/2208.12600


We study the dependence of primordial nuclear abundances on fundamental nuclear observables such as binding energies, scattering lengths, neutron lifetime, \textit{etc.} by varying these quantities. The numerical computations were performed with four publicly available codes, thus facilitating an investigation of the model-dependent (systematic) uncertainties on these dependences. Indeed deviations of the order of a few percent are found. Moreover, accounting for the temperature dependence of the sensitivity of the rates to some relevant parameters leads to a reduction of the sensitivity of the final primordial abundances, which in some cases is appreciable. These effects are considered to be relevant for studies of the dependence of the nuclear abundances on fundamental parameters such as quark masses or couplings underlying the nuclear parameters studied here.

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U. Meißner and B. Metsch
Mon, 29 Aug 22
10/49

Comments: 13 pages, 6 figures

First-order electroweak phase transitions: a nonperturbative update [CL]

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http://arxiv.org/abs/2205.07238


We study first-order electroweak phase transitions nonperturbatively, assuming any particles beyond the Standard Model are sufficiently heavy to be integrated out at the phase transition. Utilising high temperature dimensional reduction, we perform lattice Monte-Carlo simulations to calculate the main quantities characterising the transition: the critical temperature, the latent heat, the surface tension and the bubble nucleation rate, updating and extending previous lattice studies. We focus on the region where the theory gives first-order phase transitions due to an effective reduction in the Higgs self-coupling and give a detailed comparison with perturbation theory.

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O. Gould, S. Güyer and K. Rummukainen
Tue, 17 May 22
50/95

Comments: 22 pages, 17 figures, for videos of bubble nucleation see this https URL, and for the dataset see this https URL

Power spectrum of domain-wall network and its implications for isotropic and anisotropic cosmic birefringence [CEA]

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http://arxiv.org/abs/2205.05083


Recently, based on a novel analysis of the Planck satellite data, a hint of a uniform rotation of the polarization of cosmic microwave background photons, called isotropic cosmic birefringence, has been reported. The suggested rotation angle of polarization of about $0.2-0.4$ degrees strongly suggests that it is determined by the fine structure constant, which can be naturally explained over a very wide parameter range by the domain walls of axion-like particles. Interestingly, the axion-like particle domain walls predict not only isotropic cosmic birefringence but also anisotropic one that reflects the spatial distribution of the axion-like particle field on the last scattering surface. In this Letter, we perform lattice simulations of the formation and evolution of domain walls in the expanding universe and obtain for the first time the two-point correlation function and power spectrum of the scalar field that constitutes the domain walls. We find that while the power spectrum is generally consistent with analytical predictions based on random wall distributions, there is a predominant excess on the scale corresponding to the Hubble radius. Applying our results to the anisotropic cosmic birefringence, we predict the power spectrum of the rotation angles induced by the axion-like particle domain walls and show that it is within the reach of future observations of the cosmic microwave background.

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N. Kitajima, F. Kozai, F. Takahashi, et. al.
Thu, 12 May 22
3/63

Comments: 8pages, 7figures

Alpha-alpha scattering in the Multiverse [CL]

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http://arxiv.org/abs/2112.09409


We investigate the phase shifts of low-energy $\alpha$-$\alpha$ scattering under variations of the fundamental parameters of the Standard Model, namely the light quark mass, the electromagnetic fine-structure constant as well as the QCD $\theta$-angle. As a first step, we recalculate $\alpha$-$\alpha$ scattering in our Universe utilizing various improvements in the adiabatic projection method, which leads to an improved, parameter-free prediction of the S- and D-wave phase shifts for laboratory energies below 10~MeV. We find that positive shifts in the pion mass have a small effect on the S-wave phase shift, whereas lowering the pion mass tends to unbind the two-alpha system, limiting such variations to less than 7%. The effect on the D-wave phase shift turns out to be more pronounced as signaled by the D-wave resonance parameters. Variations of the fine-structure constant have almost no effect on the low-energy $\alpha$-$\alpha$ phase shifts. We further show that up-to-and-including next-to-leading order in the chiral expansion, variations of these phase shifts with respect to the QCD $\theta$-angle can be expressed in terms of the $\theta$-dependent pion mass.

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S. Elhatisari, T. Lähde, D. Lee, et. al.
Mon, 20 Dec 21
33/59

Comments: 22 pages, 8 figures

Lattice Simulation of Multi-Stream Inflation [CEA]

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http://arxiv.org/abs/2110.05268


We present the first lattice simulation to investigate the nature of multi-stream inflation. The simulation confirms the physical picture of multi-stream inflation, and with new findings in parameter space and field behaviors. Our simulation shows that gradient energy plays a significant role in multi-stream inflation. For a double field potential with a shifted Gaussian barrier, bifurcation probability is controlled by the shift distance with an error function relation. The bubbles created by bifurcation tend to be more spherical as bifurcation probability decreases. Also, the bifurcation is more likely to introduce oscillations of field values inside the bubbles than outside.

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T. Cai, J. Jiang and Y. Wang
Tue, 12 Oct 21
12/73

Comments: 8 pages, 15 figures

Peaks of sound velocity in two color dense QCD: quark saturation effects and semishort range correlations [CL]

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http://arxiv.org/abs/2110.02100


We discuss stiffening of dense matter in two color QCD (QC$_2$D) where hadrons are mesons and diquark baryons. We study two models which describe a transition of matter from the Bose-Einstein-Condensation regime at low density to the Bardeen-Cooper-Schrieffer regime at high density. The first model is based on coherent states of diquarks, and the second is the Nambu-Jona-Lasinio model with diquark pairing terms. We particularly focus on how quark states are occupied as baryon density increases. We find that, due to the occupied quark levels, the ideal gas picture of diquarks breaks down at density significantly less than the density where baryon cores overlap. The saturation of quark states at low momenta stiffens equations of state. We also study the effects of interactions which depend on the quark occupation probability. We argue that equations of state become very stiff when the bulk part of the quark Fermi sea has the effective repulsion but the Fermi surface enjoys the attractive correlations. This disparity for different momentum domains is possible due to the strong channel dependence in gluon exchanges with momentum transfer of $0.2-1$ GeV. These concepts can be transferred from QC$_2$D to QCD in any numbers of colors.

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T. Kojo and D. Suenaga
Wed, 6 Oct 21
20/56

Comments: 14 pages, 14 figures

Dark Confinement and Chiral Phase Transitions: Gravitational Waves vs Matter Representations [CL]

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http://arxiv.org/abs/2109.11552


We study the gravitational-wave signal stemming from strongly coupled models featuring both, dark chiral and confinement phase transitions. We therefore identify strongly coupled theories that can feature a first-order phase transition. Employing the Polyakov-Nambu-Jona-Lasinio model, we focus our attention on SU(3) Yang-Mills theories featuring fermions in fundamental, adjoint, and two-index symmetric representations. We discover that for the gravitational-wave signals analysis, there are significant differences between the various representations. Interestingly we also observe that the two-index symmetric representation leads to the strongest first-order phase transition and therefore to a higher chance of being detected by the Big Bang Observer experiment. Our study of the confinement and chiral phase transitions is further applicable to extensions of the Standard Model featuring composite dynamics.

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M. Reichert, F. Sannino, Z. Wang, et. al.
Mon, 27 Sep 21
33/68

Comments: 27 pages, 12 figures, 4 tables

Hubble-induced phase transitions on the lattice with applications to Ricci reheating [CL]

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http://arxiv.org/abs/2107.09671


Using 3+1 classical lattice simulations, we follow the symmetry breaking pattern and subsequent non-linear evolution of a spectator field non-minimally coupled to gravity when the post-inflationary dynamics is given in terms of a stiff equation-of-state parameter. We find that the gradient energy density immediately after the transition represents a non-negligible fraction of the total energy budget, steadily growing to equal the kinetic counterpart. This behaviour is reflected on the evolution of the associated equation-of-state parameter, which approaches a universal value $1/3$, independently of the shape of non-linear interactions. Combined with kination, this observation allows for the generic onset of radiation domination for arbitrary self-interacting potentials, significantly extending previous results in the literature. The produced spectrum at that time is, however, non-thermal, precluding the naive extraction of thermodynamical quantities like temperature. Potential identifications of the spectator field with the Standard Model Higgs are also discussed.

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D. Bettoni, A. Lopez-Eiguren and J. Rubio
Thu, 22 Jul 21
15/59

Comments: 26 pages, 12 figures, 1 appendix. Computer generated movies of the simulation are available at this https URL

Probing the $B+L$ violation process with the observation of cosmic magnetic field [CL]

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http://arxiv.org/abs/2107.08978


We numerically investigate the $B+L$ violation process by performing three-dimensional lattice simulations of a unified scenario of first-order phase transitions and the sphaleron generation. The simulation results indicate that the Chern-Simons number changes along with the helical magnetic field production when the sphaleron decay occurs. Based on these numerical results, we then propose a novel method to probe the baryon asymmetry generation of the Universe, which is a general consequence of the electroweak sphaleron process, through the astronomical observation of corresponding helical magnetic fields.

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Y. Di, J. Wang, L. Bian, et. al.
Tue, 20 Jul 21
99/104

Comments: 6 pages, 4 figures

Thermal quarks and gluon propagators in two-color dense QCD [CL]

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http://arxiv.org/abs/2102.07231


We study Landau gauge gluon propagators in two-color QCD at finite quark chemical potential ($\mu_q$) and temperature ($T$). We include medium polarization effects at one-loop by quarks into massive gluon propagators, and compared the analytic results with the available lattice data. We particularly focus on the high density phase of color-singlet diquark condensates whose critical temperature is $\sim 100$ MeV with weak dependence on $\mu_q$. At zero temperature the color singlet condensates protect the IR limit of electric and magnetic gluon propagators from the medium screening effects. At finite temperature, this behavior remains true for the magnetic sector, but the electric screening mass should be generated by thermal, and hence gapless, particles which are unbound from the diquark condensates. Treating thermal excitations as quasi-quarks, we found that the electric screening develops too fast compared to the lattice results. Beyond the critical temperature for diquark condensates the analytic results are consistent with the lattice results.

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T. Kojo and D. Suenaga
Tue, 16 Feb 21
42/63

Comments: 10 pages, 10 figures

First-Order Quantum Correction in Coherent State Expectation Value of Loop-Quantum-Gravity Hamiltonian: I. Overview and Results [CL]

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http://arxiv.org/abs/2012.14242


Given the Loop-Quantum-Gravity (LQG) non-graph-changing Hamiltonian $\widehat{H[N]}$, the coherent state expectation value $\langle\widehat{H[N]}\rangle$ admits an semiclassical expansion in $\ell^2_{\rm p}$. In this paper, we compute explicitly the expansion of $\langle\widehat{H[N]}\rangle$ on the cubic graph to the linear order in $\ell^2_{\rm p}$, when the coherent state is peaked at the homogeneous and isotropic data of cosmology. In our computation, a powerful algorithm is developed to overcome the complexity in computing $\langle \widehat{H[N]} \rangle$. In particular, some key innovations in our algorithm substantially reduce the computational complexity in the Lorentzian part of $\langle\widehat{H[N]}\rangle$. In addition, some effects in cosmology from the quantum correction in $\langle\widehat{H[N]}\rangle$ are discussed at the end of this paper.

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C. Zhang, S. Song and M. Han
Wed, 10 Feb 21
9/64

Comments: 29 pages, 2 figures, Theorem 4.4 is revised

First-Order Quantum Correction in Coherent State Expectation Value of Loop-Quantum-Gravity Hamiltonian: II. Detailed Derivations [CL]

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http://arxiv.org/abs/2102.03591


Given the non-graph-changing Hamiltonian $\widehat{H[N]}$ in Loop Quantum Gravity (LQG), $\langle\widehat{H[N]}\rangle$, the coherent state expectation value of $\widehat{H[N]}$, admits an semiclassical expansion in $\ell^2_{\rm p}$. In this paper, as presenting the detailed derivations of our previous work arXiv:2012.14242, we explicitly compute the expansion of $\langle\widehat{H[N]}\rangle$ to the linear order in $\ell^2_{\rm p}$ on the cubic graph with respect to the coherent state peaked at the homogeneous and isotropic data of cosmology. In our computation, a powerful algorithm is developed, supported by rigorous proofs and several theorems, to overcome the complexity in the computation of $\langle \widehat{H[N]} \rangle$. Particularly, some key innovations in our algorithm substantially reduce the complexity in computing the Lorentzian part of $\langle\widehat{H[N]}\rangle$. Additionally, some quantum correction effects resulted from $\langle\widehat{H[N]}\rangle$ in cosmology are discussed at the end of this paper.

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C. Zhang, S. Song and M. Han
Wed, 10 Feb 21
35/64

Comments: 53+11 pages, 2 figures, presenting the detailed derivations of our previous work arXiv:2012.14242

CosmoLattice [CEA]

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http://arxiv.org/abs/2102.01031


This is the user manual for CosmoLattice, a modern package for lattice simulations of the dynamics of interacting scalar and gauge fields in an expanding universe. CosmoLattice incorporates a series of features that makes it very versatile and powerful: $i)$ it is written in C++ fully exploiting the object oriented programming paradigm, with a modular structure and a clear separation between the physics and the technical details, $ii)$ it is MPI-based and uses a discrete Fourier transform parallelized in multiple spatial dimensions, which makes it specially appropriate for probing scenarios with well-separated scales, running very high resolution simulations, or simply very long ones, $iii)$ it introduces its own symbolic language, defining field variables and operations over them, so that one can introduce differential equations and operators in a manner as close as possible to the continuum, $iv)$ it includes a library of numerical algorithms, ranging from $O(\delta t^2)$ to $O(\delta t^{10})$ methods, suitable for simulating global and gauge theories in an expanding grid, including the case of `self-consistent’ expansion sourced by the fields themselves. Relevant observables are provided for each algorithm (e.g.~energy densities, field spectra, lattice snapshots) and we note that remarkably all our algorithms for gauge theories always respect the Gauss constraint to machine precision. In this manual we explain how to obtain and run CosmoLattice in a computer (let it be your laptop, desktop or a cluster). We introduce the general structure of the code and describe in detail the basic files that any user needs to handle. We explain how to implement any model characterized by a scalar potential and a set of scalar fields, either singlets or interacting with $U(1)$ and/or $SU(2)$ gauge fields. CosmoLattice is publicly available at www.cosmolattice.net.

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D. Figueroa, A. Florio, F. Torrenti, et. al.
Tue, 2 Feb 21
53/86

Comments: 111 pages, 3 figures and O(100) code files

Axion hot dark matter bound, reliably [CL]

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http://arxiv.org/abs/2101.10330


We show that the commonly adopted hot dark matter (HDM) bound on the axion mass $m_a \lesssim$ 1 eV is not reliable, since it is obtained by extrapolating the chiral expansion in a region where the effective field theory breaks down. This is explicitly shown via the calculation of the axion-pion thermalization rate at the next-to-leading order in chiral perturbation theory. We finally advocate a strategy for a sound extraction of the axion HDM bound via lattice QCD techniques.

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L. Luzio, G. Martinelli and G. Piazza
Wed, 27 Jan 21
40/68

Comments: 7 pages, 3 figures

Real scalar phase transitions: a nonperturbative analysis [CL]

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http://arxiv.org/abs/2101.05528


We study the thermal phase transitions of a generic real scalar field, without a $Z_2$-symmetry, referred to variously as an inert, sterile or singlet scalar, or $\phi^3+\phi^4$ theory. Such a scalar field arises in a wide range of models, including as the inflaton, or as a portal to the dark sector. At high temperatures, we perform dimensional reduction, matching to an effective theory in three dimensions, which we then study both perturbatively and on the lattice. For strong first-order transitions, with large tree-level cubic couplings, our lattice Monte-Carlo simulations agree with perturbation theory within error. However, as the size of the cubic coupling decreases, relative to the quartic coupling, perturbation theory becomes less and less reliable, breaking down completely in the approach to the $Z_2$-symmetric limit, in which the transition is of second order. Notwithstanding, the renormalisation group is shown to significantly extend the validity of perturbation theory. Throughout, our calculations are made as explicit as possible so that this article may serve as a guide for similar calculations in other theories.

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O. Gould
Fri, 15 Jan 21
48/60

Comments: 41 pages, 14 figures

Magnetic field and gravitational waves from the first-order Phase Transition [CEA]

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http://arxiv.org/abs/2012.15625


In this letter, we study the productions of magnetic fields and gravitational waves from the first-order phase transition. We perform numerical simulations of the evolutions of Higgs fields, and gauge fields after supplementing the bubble nucleations and obtain the power-law spectra of the gravitational wave and the magnetic field strength. Our study suggests that the observation of cosmic magnetic field strength and the gravitational waves can be complementary to probe features of first-order phase transitions occurring in the early Universe.

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Y. Di, J. Wang, R. Zhou, et. al.
Fri, 1 Jan 21
63/103

Comments: 6 pages, 4 figures, comments welcome!

Magnetic field and gravitational waves from the first-order Phase Transition [CEA]

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http://arxiv.org/abs/2012.15625


In this letter, we study the productions of magnetic fields and gravitational waves from the first-order phase transition. We perform numerical simulations of the evolutions of Higgs fields, and gauge fields after supplementing the bubble nucleations and obtain the power-law spectra of the gravitational wave and the magnetic field strength. Our study suggests that the observation of cosmic magnetic field strength and the gravitational waves can be complementary to probe features of first-order phase transitions occurring in the early Universe.

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Y. Di, J. Wang, R. Zhou, et. al.
Fri, 1 Jan 21
62/103

Comments: 6 pages, 4 figures, comments welcome!

Fun with colours: the standard model with two colour QCD has radically different long distance physics [CL]

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http://arxiv.org/abs/2012.13856


In our world the standard model of particle physics contains within it the fairly intractable theory called QCD. A toy version with two colours is often studied as a model confining and chiral symmetry breaking field theory. Here we investigate the cascade of changes at various distance scales if we make this change within the standard model. It is possible to limit the changes at the hadronic scale. However, the minor changes that occur actually cascade down to the far infrared, into nuclear and atomic physics, and chemistry. Through this it also possibly affects the evolution of stars and galaxies. We remark on this unexpected sensitivity of the universe to physics at the scale of quarks.

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S. Datta, S. Gupta and R. Sharma
Tue, 29 Dec 20
44/66

Comments: Submitted to Indian Journal of Physics memorial issue for Pushan Majumdar

Fun with colours: the standard model with two colour QCD has radically different long distance physics [CL]

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http://arxiv.org/abs/2012.13856


In our world the standard model of particle physics contains within it the fairly intractable theory called QCD. A toy version with two colours is often studied as a model confining and chiral symmetry breaking field theory. Here we investigate the cascade of changes at various distance scales if we make this change within the standard model. It is possible to limit the changes at the hadronic scale. However, the minor changes that occur actually cascade down to the far infrared, into nuclear and atomic physics, and chemistry. Through this it also possibly affects the evolution of stars and galaxies. We remark on this unexpected sensitivity of the universe to physics at the scale of quarks.

Read this paper on arXiv…

S. Datta, S. Gupta and R. Sharma
Tue, 29 Dec 20
53/66

Comments: Submitted to Indian Journal of Physics memorial issue for Pushan Majumdar

Fun with colours: the standard model with two colour QCD has radically different long distance physics [CL]

Posted on by

http://arxiv.org/abs/2012.13856


In our world the standard model of particle physics contains within it the fairly intractable theory called QCD. A toy version with two colours is often studied as a model confining and chiral symmetry breaking field theory. Here we investigate the cascade of changes at various distance scales if we make this change within the standard model. It is possible to limit the changes at the hadronic scale. However, the minor changes that occur actually cascade down to the far infrared, into nuclear and atomic physics, and chemistry. Through this it also possibly affects the evolution of stars and galaxies. We remark on this unexpected sensitivity of the universe to physics at the scale of quarks.

Read this paper on arXiv…

S. Datta, S. Gupta and R. Sharma
Tue, 29 Dec 20
21/66

Comments: Submitted to Indian Journal of Physics memorial issue for Pushan Majumdar

Testing the Dark Confined Landscape: From Lattice to Gravitational Waves [CL]

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http://arxiv.org/abs/2012.11614


We investigate dark sectors made of $SU(N)$ Yang-Mills confined theories coupled mainly gravitationally to our world. We employ state-of-the-art lattice results combined with effective field theory approaches to infer the dark deconfinement phase transition impact on gravitational-wave generation and detection in the early universe. For any number of dark colours $N$ larger than two, we demonstrate via a detailed analysis of the induced gravitational-waves that the landscape of dark strong sectors will be strongly constrained by future gravitational-wave detection experiments such as LISA, the Big Bang Observer, and DECIGO in the GeV range and by the Einstein Telescope and Cosmic Explorer in the TeV region.

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W. Huang, M. Reichert, F. Sannino, et. al.
Wed, 23 Dec 20
20/72

Comments: 15 pages, 12 figues

Gravitational tests of electroweak relaxation [CEA]

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http://arxiv.org/abs/2011.05795


We consider a scenario in which the electroweak scale is stabilized via the relaxion mechanism during inflation, focussing on the case in which the back-reaction potential is generated by the confinement of new strongly interacting vector-like fermions. If the reheating temperature is sufficiently high to cause the deconfinement of the new strong interactions, the back-reaction barrier then disappears and the Universe undergoes a second relaxation phase. This phase stops when the temperature drops sufficiently for the back-reaction to form again. We identify the regions of parameter space in which the second relaxation phase does not spoil the successful stabilization of the electroweak scale. In addition, the generation of the back-reaction potential that ends the second relaxation phase can be associated to a strong first order phase transition. We then study when such transition can generate a gravitational wave signal in the range of detectability of future interferometer experiments.

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D. Barducci, E. Bertuzzo and M. Arteaga-Tupia
Thu, 12 Nov 20
51/68

Comments: 34 pages, 7 figures

Pion condensation in the early Universe at nonvanishing lepton flavor asymmetry and its gravitational wave signatures [CL]

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http://arxiv.org/abs/2009.02309


We investigate the possible formation of a Bose-Einstein condensed phase of pions in the early Universe at nonvanishing values of lepton flavor asymmetries. A hadron resonance gas model with pion interactions, based on first-principle lattice QCD simulations at nonzero isospin density, is used to evaluate cosmic trajectories at various values of electron, muon, and tau lepton asymmetries that satisfy the available constraints on the total lepton asymmetry. The cosmic trajectory can pass through the pion condensed phase if the combined electron and muon asymmetry is sufficiently large: $|l_e + l_{\mu}| \gtrsim 0.1$, with little sensitivity to the difference $l_e – l_\mu$ between the individual flavor asymmetries. Future constraints on the values of the individual lepton flavor asymmetries will thus be able to either confirm or rule out the condensation of pions during the cosmic QCD epoch. We demonstrate that the pion condensed phase leaves an imprint both on the spectrum of primordial gravitational waves and on the mass distribution of primordial black holes at the QCD scale e.g. the black hole binary of recent LIGO event GW190521 can be formed in that phase.

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V. Vovchenko, B. Brandt, F. Cuteri, et. al.
Mon, 7 Sep 20
-1424/68

Comments: 10 pages, 10 figures

The cosmic QCD transition for large lepton flavour asymmetries [CL]

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http://arxiv.org/abs/2009.00036


We study the impact of large lepton flavour asymmetries on the cosmic QCD transition. Scenarios of unequal lepton flavour asymmetries are observationally almost unconstrained and therefore open up a whole new parameter space in order to study the nature of the cosmic QCD transition. For very large asymmetries, we point out two limitations to our current method, namely the possible formation of a Bose-Einstein condensate of pions and the reliability of the Taylor expansion applied in this work.

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M. Middeldorf-Wygas, I. Oldengott, D. Bödeker, et. al.
Wed, 2 Sep 20
-1346/65

Comments: 10 pages, 6 figures

Structure Factors of Neutron Matter at Finite Temperature [CL]

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http://arxiv.org/abs/2008.02824


We compute continuum and infinite volume limit extrapolations of the structure factors of neutron matter at finite temperature and density. Using a lattice formulation of leading-order pionless effective field theory, we compute the momentum dependence of the structure factors at finite temperature and at densities beyond the reach of the virial expansion. The Tan contact parameter is computed and the result agrees with the high momentum tail of the vector structure factor. All errors, statistical and systematic, are controlled for. This calculation is a first step towards a model-independent understanding of the linear response of neutron matter at finite temperature, a realm until now little explored.

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A. Alexandru, P. Bedaque, E. Berkowitz, et. al.
Mon, 10 Aug 20
-787/53

Comments: 5 pages, 3 figures, data included in submission

Modifications to Gravitational Wave Equation from Canonical Quantum Gravity [CL]

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http://arxiv.org/abs/2002.00834


It is expected that the quantum nature of spacetime leaves its imprint in all semiclassical gravitational systems, at least in certain regimes, including gravitational waves. In this paper we investigate such imprints on gravitational waves within a specific framework: space is assumed to be discrete (in the form of a regular cubic lattice), and this discrete geometry is quantised following Dirac’s canonical quantisation scheme. The semiclassical behavior is then extracted by promoting the expectation value of the Hamiltonian operator on a semiclassical state to an effective Hamiltonian. Considering a family of semiclassical states representing small tensor perturbations to Minkowski background, we derive a quantum-corrected effective wave equation. The deviations from the classical gravitational wave equation are found to be encoded in a modified dispersion relation and controlled by the discreteness parameter of the underlying lattice. For finite discretisations, several interesting effects appear: we investigate the thermodynamical properties of these modified gravitons and, under certain assumptions, derive the tensor power spectrum of the cosmic microwave background. The latter is found to deviate from the classical prediction, in that an amplification of UV modes takes place. We discuss under what circumstances such effect can be in agreement with observations.

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A. Dapor and K. Liegener
Tue, 31 Mar 20
48/94

Comments: 9 pages, 3 figures

Precision calculation of the axion-nucleon coupling in chiral perturbation theory [CL]

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http://arxiv.org/abs/2001.05327


We derive the axion-nucleon interaction Lagrangian in heavy baryon chiral perturbation theory up to next-to-next-to-leading order. The effective axion-nucleon coupling is calculated to a few percent accuracy.

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T. Vonk, F. Guo and U. Meißner
Thu, 16 Jan 20
9/46

Comments: 20 pages

Yang-Mills Classical and Quantum Mechanics and Maximally Chaotic Dynamical Systems [CL]

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http://arxiv.org/abs/2001.04902


The maximally chaotic dynamical systems (DS) are the systems which have nonzero Kolmogorov entropy. The Anosov C-condition defines a reach class of hyperbolic dynamical systems that have exponential instability of the phase trajectories and positive Kolmogorov entropy and are therefore maximally chaotic. The interest in Anosov-Kolmogorov systems is associated with the attempts to understand the relaxation phenomena, the foundation of the statistical mechanics, the appearance of turbulence in fluid dynamics, the non-linear dynamics of the Yang-Mills field, the N-body system in Newtonian gravity and the relaxation phenomena in stellar systems and the Black hole thermodynamics. The classical- and quantum-mechanical properties of maximally chaotic dynamical systems, the application of the C-K theory to the investigation of the Yang-Mills dynamics and gravitational systems as well as their application in the Monte Carlo method will be presented.

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G. Savvidy
Wed, 15 Jan 20
54/66

Comments: 13 pages, 2 figures. arXiv admin note: substantial text overlap with arXiv:2001.01785

Delineating the properties of neutron star matter in cold, dense QCD [CL]

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http://arxiv.org/abs/1912.05326


The properties of dense QCD matter are delineated through the construction of equations of state which should be consistent with the low and high density limits of QCD, nuclear laboratory experiments, and the neutron star observations. These constraints, together with the causality condition of the sound velocity, are used to develop the picture of hadron-quark continuity in which hadronic matter continuously transforms into quark matter (modulo small 1st order phase transitions). The resultant unified equation of state at zero temperature and $\beta$-equilibrium, which we call Quark-Hadron-Crossover (QHC19), is consistent with the measured properties of neutron stars as well as the microphysics known for the hadron phenomenology. In particular to $\sim 10n_0$ ($n_0$: saturation density) the gluons remain as non-perturbative as in vacuum and the strangeness can be as abundant as up- and down-quarks at the core of two-solar mass neutron stars. Within our modeling the maximum mass is found less than $\simeq 2.35$ times solar mass and the baryon density at the core ranges in $\sim 5$-8$n_0$.

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T. Kojo
Thu, 12 Dec 19
35/58

Comments: 14 pages, 10 figures, talk given at 37th International Symposium on Lattice Field Theory – Lattice2019, 16-22 June 2019, Wuhan, China. arXiv admin note: text overlap with arXiv:1904.05080

GFiRe: a Gauge Field integrator for Reheating [CEA]

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http://arxiv.org/abs/1911.06827


We present a new numerical algorithm and code, ${\sf GFiRe}$, for solving the non-linear evolution of Abelian gauge fields coupled to complex scalar fields in homogeneous and isotropic spacetimes. We adopt a hybrid approach to solving the system: the spatial derivatives are discretized using standard Lattice Gauge Field Theory techniques, whereas the time evolution of the fields and scalefactor is implemented with explicit, composite, symplectic integrators. An important property of our compound algorithm is that the discretized Gauss constraint is respected exactly, regardless of the order of the symplectic integrator. This remains true even when the background expansion is computed “self-consistently”; that is, when the expansion history is computed using spatial averaged components of the energy momentum tensor in the simulation volume. Hence, our code can also be used in cases where the fields dominate the energy density of the universe, for example, during reheating after inflation.
We test the algorithm in scenarios of reheating where the inflaton is a complex scalar field with a potential $\propto(2|\varphi|^2-v^2)^2$ and is coupled to an Abelian gauge field. Tracing the evolution of the system through complex dynamics (including resonant excitation of fields, backreaction, formation of solitons, and changes in the equation of state) in a self-consistently expanding universe, we find the energy conservation violation ($<10^{-4}$) to be very stable and the Gauss constraint violation ($<10^{-6}$) to be dominated by differencing noise.

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K. Lozanov and M. Amin
Tue, 19 Nov 19
35/65

Comments: 35 pages, 13 figures

Higher Order Hamiltonian Monte Carlo Sampling for Cosmological Large-Scale Structure Analysis [CEA]

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http://arxiv.org/abs/1911.02667


We investigate higher order symplectic integration strategies within Bayesian cosmic density field reconstruction methods. In particular, we study the fourth order discretisation of Hamiltonian equations of motion. This is achieved through an operator formalism, in which the original leap-frog algorithm is recursively applied in a combination of two forward time integration steps with an intermediate backward step with appropriate step-sizes. We restrict this study to the lognormal-Poisson model applied to a full volume halo catalogue in real space on a cubical mesh of 1250 h^{-1} Mpc side and 256^3 cells. Hence, we neglect selection effects, redshift space distortions, and displacements. We note that those observational and cosmic evolution effects can be accounted for in subsequent Gibbs-sampling steps within the COSMIC BIRTH algorithm. We find that going from the usual second to fourth order in the leap-frog scheme improves the convergence by a factor of ~20 in computing time, increasing the acceptance rate from 52 to 79%. Moreover, we obtain a correlation length of about 10 iterations, as opposed to ~300. This gain in computational efficiency is crucial to go towards a full Bayesian analysis of the cosmological large-scale structure for upcoming galaxy surveys.

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M. Hernández-Sánchez, F. Kitaura, M. Ata, et. al.
Mon, 11 Nov 19
4/105

Comments: 13 pages, 8 figures, 3 tables

Theory Summary at Strangeness in Quark Matter 2019 [CL]

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http://arxiv.org/abs/1911.01328


This is the theory summary of Strangeness in Quark Matter 2019 conference. Results include the state-of-the-art updates to the Quantum Chromodynamics (QCD) phase diagram with contributions both from heavy-ion collisions and nuclear astrophysics, studies on the QCD freeze-out lines, and several aspects regarding small systems including collectivity, heavy flavor dynamics, strangeness, and hard probes.

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J. Noronha-Hostler
Tue, 5 Nov 19
41/72

Comments: 7 pages, 1 figure, proceedings from the 18th International Conference on Strangeness in Quark Matter (SQM 2019)

Glueball scattering cross section in lattice SU(2) Yang-Mills theory [CL]

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http://arxiv.org/abs/1910.07756


We calculate the scattering cross section between $0^{++}$ glueballs of the SU(2) Yang-Mills theory on lattice using the indirect (HAL QCD) method. We employ the cluster-decomposition error reduction technique and use all space-time symmetries to improve the signal. The relation between the interglueball cross section and the scale parameter $\Lambda$ is determined as $\sigma_{\phi \phi}$ = (3.5 – 8.0) $\Lambda^{-2}$ (stat.+sys.). From the observational constraints of galactic collisions, we obtain the lower bound $\Lambda$ > 60 MeV. We also discuss the naturalness of the Yang-Mills theory as the theory explaining dark matter.

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N. Yamanaka, H. Iida, A. Nakamura, et. al.
Fri, 18 Oct 19
62/77

Comments: 9 pages, 9 figures. Full paper of the letter arXiv:1910.01440 [hep-ph]

Chiral instabilities & the onset of chiral turbulence in QED plasmas [CL]

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http://arxiv.org/abs/1910.01654


We present a first principles study of chiral plasma instabilities and the onset of chiral turbulence in QED plasmas far from equilibrium. By performing classical-statistical lattice simulations of the microscopic theory, we show that the generation of strong helical magnetic fields from a helicity imbalance in the fermion sector proceeds via three distinct phases. During the initial linear instability regime the helicity imbalance of the fermion sector causes an exponential growth(damping) of magnetic field modes with right(left) handed polarization, for which we extract the characteristic growth (damping) rates. Secondary growth of unstable modes accelerates the helicity transfer from fermions to gauge fields and ultimately leads to the emergence of a self-similar scaling regime characteristic of decaying turbulence, where magnetic helicity is efficiently transferred to macroscopic length scales. Within this turbulent regime the evolution of magnetic helicity spectrum can be described by an infrared power-spectrum with spectral exponent $\kappa$ and dynamical scaling exponents $\alpha,\beta$, which we determine from our simulations.

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M. Mace, N. Mueller, S. Schlichting, et. al.
Mon, 7 Oct 19
38/42

Comments: 10 pages, 6 figures

Dark matter scattering cross section in Yang-Mills theory [CL]

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http://arxiv.org/abs/1910.01440


We calculate for the first time the scattering cross section between lightest glueballs in SU(2) pure Yang-Mills theory, which are good candidates of dark matter. In the first step, we evaluate the interglueball potential on lattice using the time-dependent formalism of the HAL QCD method, with one lattice spacing. The statistical accuracy is improved by employing the cluster-decomposition error reduction technique and by using all space-time symmetries. We then derive the scattering phase shift and the scattering cross section at low energy, which is compared with the observational constraint on the dark matter self-scattering. We determine the lower bound on the scale parameter of the SU(2) Yang-Mills theory, as $\Lambda$ > 60 MeV.

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N. Yamanaka, H. Iida, A. Nakamura, et. al.
Fri, 4 Oct 19
47/61

Comments: 4 pages, 2 figures. Letter. It will be followed by a full paper

Structure Factors of The Unitary Gas Under Supernova Conditions [CL]

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http://arxiv.org/abs/1907.03914


We compute with lattice field theory the vector and axial static structure factors of the unitary gas for arbitrary temperature above the superfluid transition and for fugacities 0.1 < z < 1.0. Using the lattice formulation, we calculate beyond the validity of the virial expansion, a commonly used technique in many-body physics. We find qualitative differences in the behavior of the structure factors at high fugacity compared to the predictions of the virial expansion. Due to the large scattering length of neutrons, we expect the unitary gas structure factors to approximate the structure factors of hot neutron gases, and we therefore expect our calculations to be useful in supernova simulations, where neutron gas structure factors are needed to compute in-medium neutrino-neutron scattering rates.

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A. Alexandru, P. Bedaque and N. Warrington
Wed, 10 Jul 19
7/53

Comments: 10 pages, 6 figures, 1 table

Gluon propagator in two-color dense QCD: Massive Yang-Mills approach at one-loop [CL]

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http://arxiv.org/abs/1905.08751


We study the Landau gauge gluon propagators in dense two-color QCD at quark chemical potential, $\mu_q$, in the range from 0.5 to 1.0 GeV not reachable by the perturbative method at weak coupling. In order to take into account the non-perturbative effects, at tree level we use the massive Yang-Mills theory which has successfully described the lattice results of the gluon and ghost propagators in the Landau gauge. We couple quarks to this theory and compute the one-loop polarization effects. The presence of the gluon mass significantly tempers the medium effects and uncertainties associated with the strong coupling constant $\alpha_s$. The diquark condensate in two-color QCD is color-singlet, for which neither electric nor magnetic screening masses should appear at the scale less than the diquark gap. The presence of the gap helps to explain the lattice results which are not very sensitive to the quark density. Meanwhile, we also found the limitation of the one-loop estimate as well as the lack of some physics in perturbative medium corrections.

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D. Suenaga and T. Kojo
Wed, 22 May 19
11/59

Comments: 17 pages, 11 figures

Trinity of Strangeon Matter [HEAP]

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http://arxiv.org/abs/1904.11153


Strangeon is proposed to be the constituent of bulk strong matter, as an analogy of nucleon for an atomic nucleus. The nature of both nucleon matter (2 quark flavors, {\it u} and {\it d}) and strangeon matter (3 flavors, {\it u}, {\it d} and {\it s}) are controlled by the strong-force, but the baryon number of the former is much smaller than that of the latter, to be separated by a critical number of $A_{\rm c}\sim 10^9$. While micro nucleon matter (i.e., nuclei) is focused by nuclear physicists, astrophysical/macro strangeon matter could be manifested in the form of compact stars (strangeon star), cosmic rays (strangeon cosmic ray), and even dark matter (strangeon dark matter). This trinity of strangeon matter is explained, that may impact dramatically on today’s physics.

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R. Xu
Fri, 26 Apr 19
49/69

Comments: AIP Conference Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy (January 3 – 7, 2019, Xiamen, China)

Effects of the QCD Equation of State and Lepton Asymmetry on Primordial Gravitational Waves [CL]

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http://arxiv.org/abs/1904.01046


Using the quantum chromodynamics (QCD) equation of state (EoS) from lattice calculations we investigate effects from QCD on primordial gravitational waves (PGWs) produced during the inflationary era. We also consider different cases for vanishing and nonvanishing lepton asymmetry where the latter one is constrained by cosmic microwave background experiments. Our results show that there is up to a few percent deviation in the predicted gravitational wave background in the frequency range around the QCD transition ($10^{-10}- 10^{-7}$~Hz) for different lattice QCD EoSs, or at larger frequencies for nonvanishing lepton asymmetry using perturbative QCD. Future gravitational wave experiments with high enough sensitivity in the measurement of the amplitude of PGWs like SKA, EPTA, DECIGO and LISA can probe these differences and can shed light on the real nature of the cosmic QCD transition and the existence of a nonvanishing lepton asymmetry in the early universe.

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F. Hajkarim, J. Schaffner-Bielich, S. Wystub, et. al.
Wed, 3 Apr 19
24/68

Comments: 8 pages, 9 figures

Nonperturbative analysis of the gravitational waves from a first-order electroweak phase transition [CL]

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http://arxiv.org/abs/1903.11604


We present the first end-to-end nonperturbative analysis of the gravitational wave power spectrum from a thermal first-order electroweak phase transition (EWPT), using the framework of dimensionally reduced effective field theory and pre-existing nonperturbative simulation results. We are able to show that a first-order EWPT in any beyond the Standard Model (BSM) scenario that can be described by a Standard Model-like effective theory at long distances will produce gravitational wave signatures too weak to be observed at existing and planned detectors. This implies that colliders are likely to provide the best chance of exploring the phase structure of such theories, while transitions strong enough to be detected at gravitational wave experiments require either previously neglected higher-dimension operators or light BSM fields to be included in the dimensionally reduced effective theory and therefore necessitate dedicated nonperturbative studies. As a concrete application, we analyze the real singlet-extended Standard Model and identify regions of parameter space with single-step first-order transitions, comparing our findings to those obtained using a fully perturbative method. We discuss the prospects for exploring the electroweak phase diagram in this model at collider and gravitational wave experiments in light of our nonperturbative results.

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O. Gould, J. Kozaczuk, L. Niemi, et. al.
Fri, 29 Mar 19
50/78

Comments: 18 pages + references, 6 figures

Bounds on the Equation of State of Neutron Stars from High Energy Deeply Virtual Exclusive Experiments [CL]

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http://arxiv.org/abs/1812.01479


The recent detection of gravitational waves from merging neutron star events has opened a new window on the many unknown aspects of their internal dynamics. A key role in this context is played by the transition from baryon to quark matter described in the neutron star equation of state (EoS). In particular, the binary pulsar observation of heavy neutron stars requires appropriately stiff dense matter in order to counter gravitational collapse, at variance with the predictions of many phenomenological quark models. On the other side, the LIGO observations favor a softer EoS therefore providing a lower bound to the equation stiffness. We introduce a quantum chromodynamics (QCD) description of the neutron star’s high baryon density regime where the pressure and energy density distributions are directly obtained from the matrix elements of the QCD energy momentum tensor. Recent ab initio calculations allow us to evaluate the energy-momentum tensor in a model independent way including both quark and gluon degrees of freedom. Our approach is a first effort to replace quark models and effective gluon interactions with a first principles, fully QCD-based description. Most importantly, the QCD energy momentum tensor matrix elements are connected to the Mellin moments of the generalized parton distributions which can be measured in deeply virtual exclusive scattering experiments. As a consequence, we establish a connection between observables from high energy experiments and from the analysis of gravitational wave events. Both can be used to mutually constrain the respective sets of data. In particular, the emerging QCD-based picture is consistent with the GW170817 neutron star merger event once we allow a first-order phase transition from a low-density nuclear matter EoS to the newly-constructed high-density quark-gluon one.

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S. Liuti, A. Rajan and K. Yagi
Fri, 7 Dec 18
60/66

Comments: 5 pages, 3 figures

The cosmic QCD epoch at non-vanishing lepton asymmetry [CL]

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http://arxiv.org/abs/1807.10815


We investigate how lepton asymmetry impacts the cosmic trajectory in the QCD phase diagram. We study the evolution of chemical potentials during the QCD epoch of the early Universe using susceptibilities from lattice QCD to interpolate between an ideal quark gas and an ideal hadron resonance gas. The lepton asymmetry affects the evolution of all chemical potentials. The standard cosmic trajectory is obtained assuming tiny lepton and baryon asymmetries. For larger lepton asymmetry, the charge chemical potential exceeds the baryon chemical potential before pion annihilation.

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M. Wygas, I. Oldengott, D. Bodeker, et. al.
Tue, 31 Jul 18
2/69

Comments: 6 pages, 2 figures

"Invisible" QCD axion rolling through the QCD phase transition [CL]

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http://arxiv.org/abs/1804.05173


Visible matter in the current Universe is a consequence of the phase transition of the strong force, quantum chromodynamics (QCD). This phase transition has occurred at the Universe temperature around $T_c\simeq 165\,$MeV while it was expanding. Strongly interacting matter particles are quarks above $T_c$, while they are pions, protons and neutrons below $T_c$. The spin degrees of freedom 37 in the quark and gluon phase just above $T_c$ are converted to 3 (pions) after the phase transition. This phase transition might have been achieved mostly at supercooled temperatures. The supercooling was provided by the expansion of the Universe. We obtain the effective bubble formation rate $\alpha(T)\approx 10^{4-5}\,$MeV and the completion temperature of the phase change (to the hadronic phase), $T_f\simeq 126\,$MeV. During the phase transition, the scale factor $R$ has increased by a factor of 2.4. This provides a key knowledge on the energy density of “invisible” QCD axion at the full hadronic-phase commencement temperature $T_f$, and allows for us to estimate the current energy density of cold dark matter composed of “invisible” QCD axions.

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J. Kim and S. Kim
Tue, 17 Apr 18
44/83

Comments: LateX file of 11 pages and 7 figures

Axion energy density, bottle neck period, and $\barθ$ ratios between early and late times [CL]

Posted on by

http://arxiv.org/abs/1803.03517


The possibility of the “invisible” axion being cold dark matter relies on the acceptable estimates of the current axion energy density. The estimate depends on the nature of QCD phase transition at a few hundred MeV and the evolution of the misalignment angle $\bar{\theta}$. The onset of $\bar{\theta}$ oscillation undergoes a bottleneck period which occurred during the QCD phase transition. In addition, the anharmonic coupling of order $a^4$ affects the $\bar{\theta}$ evolution. From the time that the anharmonic effect is negligible, it is rather simple to calculate the ratio of $\bar{\theta}$’s between early and late times. For multi GHz oscillations, the current age of the Universe needs at least $10^{27}$ oscillations which limits an exact calculation of $\bar{\theta}$ . We establish a stepwise approximation for numerical solutions of the differential equation and obtain $\bar{\theta}_{\rm now}/\bar{\theta}_f\approx 3\times 10^{-17}$ for $m_a\simeq 10^{-4}\,$eV, where $t_f$ is the first time that the full hadronic phase (after the QCD phase transition) was established.

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J. Kim, S. Kim and S. Nam
Mon, 12 Mar 2018
7/45

Comments: 11 pages with 5 figures

A new class of compact stars: pion stars [CL]

Posted on by

http://arxiv.org/abs/1802.06685


Compact stellar objects offer deep insight into the physics of elementary particles in dense environments through the imprint left by merger events on the electromagnetic and gravitational wave spectra. The theoretical description of compact star interiors requires full knowledge of the equation of state (EoS) of nuclear matter and involves the non-perturbative solution of quantum chromodynamics (QCD), the theory of strongly interacting quarks and gluons. However, first-principle methods (most notably, lattice QCD simulations) are not available for high neutron densities – consequently, the EoS of neutron stars necessarily relies on a modeling of the nuclear force. Here we propose a different scenario, where the neutron density vanishes and a Bose-Einstein condensate of charged pions (the lightest excitations in QCD) plays the central role instead. This setting can be approached by first-principle methods and leads to a new class of compact stars: pion stars. As we demonstrate, pion star matter exhibits gravitationally bound configurations and is metastable against electroweak decays. If pion stars indeed exist in our Universe, this result constitutes the first occasion that the EoS and the mass-radius relation of a compact stellar object is determined from first principles within the Standard Model.

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B. Brandt, G. Endrodi, E. Fraga, et. al.
Tue, 20 Feb 18
21/54

Comments: 6 pages, 4 figures

Tensor Modes in Pure Natural Inflation [CL]

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http://arxiv.org/abs/1711.10490


We study tensor modes in pure natural inflation (arXiv:1706.08522), a recently-proposed inflationary model in which an axionic inflaton couples to pure Yang-Mills gauge fields. We find that the tensor-to-scalar ratio r is naturally bounded from below. This bound originates from the finiteness of the number of metastable branches of vacua in pure Yang-Mills theories. Details of the model can be probed by future cosmic microwave background experiments and improved lattice gauge theory calculations of the theta-angle dependence of the vacuum energy.

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Y. Nomura and M. Yamazaki
Thu, 30 Nov 17
26/77

Comments: 6 pages, 6 figures

The dark-matter axion mass [CL]

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http://arxiv.org/abs/1708.07521


We evaluate the efficiency of axion production from spatially random initial conditions in the axion field, so a network of axionic strings is present. For the first time, we perform numerical simulations which fully account for the large short-distance contributions to the axionic string tension, and the resulting dense network of high-tension axionic strings. We find nevertheless that the total axion production is somewhat less efficient than in the angle-averaged misalignment case. Combining our results with a recent determination of the hot QCD topological susceptibility (Borsanyi et al 2016), we find that if the axion makes up all of the dark matter, then the axion mass is m_a = 26.2 +-3.4 micro-electron volts.

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V. Klaer and G. Moore
Mon, 28 Aug 17
46/46

Comments: 19 pages including 8 figures and appendices

Anomalous non-conservation of fermion/chiral number in Abelian gauge theories at finite temperature [CL]

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http://arxiv.org/abs/1707.09967


We discuss the non-conservation of fermion number (or chirality breaking, depending on the fermionic charge assignment) in Abelian gauge theories at finite temperature. We study different mechanisms of fermionic charge disappearance in the high temperature plasma, with the use of both analytical estimates and real-time classical numerical simulations. We investigate the random walk of the Chern-Simons number $N_{\rm CS} \propto \int d^4x F_{\mu\nu}{\tilde F}^{\mu\nu}$, and show that it has a diffusive behaviour in the presence of an external magnetic field $B$. This indicates that the mechanism for fermionic number non-conservation for $B \neq 0$, is due to fluctuations of the gauge fields, similarly as in the case of non-Abelian gauge theories. We determine numerically the rate of chirality non-conservation associated with this diffusion, finding it larger by a factor $\sim 60$ compared to previous theoretical estimates. We also perform numerical simulations for the system which contains a chemical potential $\mu$ representing a fermionic charge density, again both with and without an external magnetic field. When $B=0$, we observe clearly the expected instability of the system for $\mu \neq 0$, as long as the chemical potential exceeds a critical value $\mu > \mu_c(L)$, which depends on the size $L$ of the system. When $B \neq 0$, the fluctuations of bosonic fields lead to the transfer of chemical potential into Chern-Simons number for arbitrary $\mu$.

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D. Figueroa and M. Shaposhnikov
Tue, 1 Aug 17
55/55

Comments: 60 pages, 20 figures

How to simulate global cosmic strings with large string tension [CL]

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http://arxiv.org/abs/1707.05566


Global string networks may be relevant in axion production in the early Universe, as well as other cosmological scenarios. Such networks contain a large hierarchy of scales between the string core scale and the Hubble scale, log(f/H) around 70, which influences the network dynamics by giving the strings large tensions T = pi f^2 log(f/H). We present a new numerical approach to simulate such global string networks, capturing the tension without an exponentially large lattice.

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V. Klaer and G. Moore
Wed, 19 Jul 17
40/58

Comments: 22 pages including 5 figures

Quantifying the sensitivity of Big Bang Nucleosynthesis to isospin breaking with input from lattice QCD [CL]

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http://arxiv.org/abs/1706.04991


We perform the first quantitative study of the sensitivity of Big Bang Nucleosynthesis to variations in isospin breaking with precise input from lattice QCD calculations. The predicted light nuclear abundances are most sensitive to the neutron-proton mass splitting as both the initial relative abundance of neutrons to protons and the $n \rightleftharpoons p$ weak reaction rates are very sensitive to this quantity. Lattice QCD has been used to determine this mass splitting to greater than 5-sigma, including contributions from both the down-quark up-quark mass splitting, $2\delta = m_d-m_u$ and from electromagnetic coupling of the quarks to the photons with a strength governed by the fine structure constant, $\alpha_{fs}$. At leading order in isospin breaking, the contribution of $\delta$ and $\alpha_{fs}$ to $M_n-M_p$ and the nuclear reaction rates can be varied independently. We use this knowledge and input from lattice QCD to quantitatively study variations of the predicted light nuclear abundances as $\delta$ and $\alpha_{fs}$ are varied. The change in the D and ${}^4$He abundances individually allow for potentially large simultaneous variations in $\delta$ and $\alpha_{fs}$ while maintaining consistency with the observed abundances, however the combined comparison restricts variations in these sources of isospin breaking to less than $\lesssim1.25\%$ at the 3-sigma confidence level. This sensitivity can be used to place tight constraints on prospective beyond the Standard Model theories that would modify these isospin breaking effects in the primordial Universe.

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M. Heffernan, P. Banerjee and A. Walker-Loud
Fri, 16 Jun 17
2/62

Comments: 10 pages, 5 figures; to be submitted to PRC

Lattice implementation of Abelian gauge theories with Chern-Simons number and an axion field [CL]

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http://arxiv.org/abs/1705.09629


Real time evolution of classical gauge fields is relevant for a number of applications in particle physics and cosmology, ranging from the early Universe to dynamics of quark-gluon plasma. We present a lattice formulation of the interaction between a $shift$-symmetric field and some $U(1)$ gauge sector, $a(x)\tilde{F}{\mu\nu}F^{\mu\nu}$, reproducing the continuum limit to order $\mathcal{O}(dx\mu^2)$ and obeying the following properties: (i) the system is gauge invariant and (ii) shift symmetry is exact on the lattice. For this end we construct a definition of the {\it topological number density} $Q = \tilde{F}{\mu\nu}F^{\mu\nu}$ that admits a lattice total derivative representation $Q = \Delta\mu^+ K^\mu$, reproducing to order $\mathcal{O}(dx_\mu^2)$ the continuum expression $Q = \partial_\mu K^\mu \propto \vec E \cdot \vec B$. If we consider a homogeneous field $a(x) = a(t)$, the system can be mapped into an Abelian gauge theory with Hamiltonian containing a Chern-Simons term for the gauge fields. This allow us to study in an accompanying paper the real time dynamics of fermion number non-conservation (or chirality breaking) in Abelian gauge theories at finite temperature. When $a(x) = a(\vec x,t)$ is inhomogeneous, the set of lattice equations of motion do not admit however a simple explicit local solution (while preserving an $\mathcal{O}(dx_\mu^2)$ accuracy). We discuss an iterative scheme allowing to overcome this difficulty.

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D. Figueroa and M. Shaposhnikov
Mon, 29 May 17
-78/35

Comments: 30 pages

Constructing a neutron star in G2-QCD [HEAP]

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http://arxiv.org/abs/1702.08724


The inner structure of neutron stars is still an open question. To make progress and understand the qualitative impact of gauge interactions on the neutron star structure we study neutron stars in a modified version of QCD. In this modification the gauge group of QCD is replaced by the exceptional Lie group G$_2$, which has neutrons and is accessible at finite density in lattice calculations. Using an equation of state constructed from lattice calculations we determine the mass-radius-relation for a neutron star in this theory using the Tolman-Oppenheimer-Volkoff equation. The results exhibit an influence of the non-trivial interactions on the mass-radius relation. However, the masses of the quarks are found to have little influence. We also give density profiles and the phase structure inside the neutron star. If the results carry over to full QCD, much of the internal structure of neutron stars could already be inferred from a precise measurement of the mass-radius relation.

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O. Hajizadeh and A. Maas
Wed, 1 Mar 17
5/67

Comments: (19 pages, 9 figures)

Ab initio calculations of the isotopic dependence of nuclear clustering [CL]

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http://arxiv.org/abs/1702.05177


Nuclear clustering describes the appearance of structures resembling smaller nuclei such as alpha particles (4He nuclei) within the interior of a larger nucleus. While clustering is important for several well-known examples, little is known about the general nature of clustering in nuclei. In this letter we present lattice Monte Carlo calculations based on chiral effective field theory for the ground states of helium, beryllium, carbon, and oxygen isotopes. By computing model-independent measures that probe three- and four-nucleon correlations at short distances, we determine the effective number of alpha clusters in any nucleus as well as their shape compared to alpha particles in vacuum. We also introduce a new computational approach called the pinhole algorithm, which solves a long-standing deficiency of auxiliary-field Monte Carlo simulations in computing density correlations relative to the center of mass. We use the pinhole algorithm to determine the proton and neutron density distributions and the geometry of cluster correlations in 12C, 14C, and 16C. The structural similarities among the carbon isotopes suggest that 14C and 16C have excitations analogous to the well-known Hoyle state resonance in 12C.

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S. Elhatisari, E. Epelbaum, H. Krebs, et. al.
Mon, 20 Feb 17
17/37

Comments: 5 + 9 pages (main + supplemental materials), 4 + 6 figures (main + supplemental materials)

Equation of state of the SU($3$) Yang-Mills theory: a precise determination from a moving frame [CL]

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http://arxiv.org/abs/1612.00265


The equation of state of the SU($3$) Yang-Mills theory is determined in the deconfined phase with a precision of about 0.5%. The calculation is carried out by numerical simulations of lattice gauge theory with shifted boundary conditions in the time direction. At each given temperature, up to $230\, T_c$ with $T_c$ being the critical temperature, the entropy density is computed at several lattice spacings so to be able to extrapolate the results to the continuum limit with confidence. Taken at face value, above a few $T_c$ the results exhibit a striking linear behaviour in $\ln(T/T_c)^{-1}$ over almost 2 orders of magnitude. Within errors, data point straight to the Stefan-Boltzmann value but with a slope grossly different from the leading-order perturbative prediction. The pressure is determined by integrating the entropy in the temperature, while the energy density is extracted from $T s=(\epsilon + p )$. The continuum values of the potentials are well represented by Pad\’e interpolating formulas, which also connect them well to the Stefan-Boltzmann values in the infinite temperature limit. The pressure, the energy and the entropy densities are compared with results in the literature. The discrepancy among previous computations near $T_c$ is analyzed and resolved thanks to the high precision achieved.

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L. Giusti and M. Pepe
Tue, 6 Dec 16
18/71

Comments: 7 pages, 3 figures

The topological susceptibility in finite temperature QCD and axion cosmology [CL]

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http://arxiv.org/abs/1606.03145


We study the topological susceptibility in 2+1 flavor QCD above the chiral crossover transition temperature using Highly Improved Staggered Quark action and several lattice spacings, corresponding to temporal extent of the lattice, $N_\tau=6,8,10$ and $12$. We observe very distinct temperature dependences of the topological susceptibility in the ranges above and below $250$ MeV. While for temperatures above $250$ MeV, the dependence is found to be consistent with dilute instanton gas approximation, at lower temperatures the fall-off of topological susceptibility is milder. We discuss the consequence of our results for cosmology wherein we estimate the bounds on the axion decay constant and the oscillation temperature if indeed the QCD axion is a possible dark matter candidate.

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P. Petreczky, H. Schadler and S. Sharma
Tue, 29 Nov 16
46/77

Comments: 19 pages and 7 figures; v2: A new figure, a few references and minor comments added; published version

Baryon number transfer could delay Quark-Hadron transition in cosmology [CEA]

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http://arxiv.org/abs/1610.05519


In the early Universe, s.i. matter was a quark-gluon plasma. Both lattice computations and heavy ion collision experiments however tell us that, in the absence of chemical potentials, no plasma survives at $T <\sim 150\, $MeV. The cosmological QH transition, however, seems to have been a crossover; cosmological consequences envisaged when it was believed to be a phase transition no longer hold. In this paper we discuss whether even a crossover transition can leave an imprint that cosmological observations can seek or, viceversa, there are questions cosmology should still ask QCD specialists. In this context, we outline, first of all, that it is still unclear how baryons (not hadrons) could form at the cosmological transition. A critical role should be played by diquark states, whose abundance in the early plasma needs to be accurately evaluated. We estimate that, if the number of quarks belonging to a diquark state, at the eve of the cosmological transition, is $<\sim 1:10^6$, its dynamics could be modified by the process of B-transfer from plasma to hadrons. In turn, by assuming B-transfer to cause just mild perturbations and, in particular, no entropy input, we study the deviations from the tracking regime, in the frame of SCDEW models. We find that, in some cases, residual deviations could propagate down to primeval nucleosynthesis.

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S. Bonometto and R. Mainini
Wed, 19 Oct 16
4/87

Comments: 15 pages, 8 figures, submitted to Universe

A G2-QCD neutron star [HEAP]

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http://arxiv.org/abs/1609.06979


The determination of the properties of neutron stars from the underlying theory, QCD, is still an unsolved problem. This is mainly due to the difficulty to obtain reliable results for the equation of state for cold, dense QCD. As an alternative route to obtain qualitative insights, we determine the structure of a neutron star for a modified version of QCD: By replacing the gauge group SU(3) with the exceptional Lie group G2, it is possible to perform lattice simulations at finite density, while still retaining neutrons. Here, results of these lattice simulations are used to determine the mass-radius relation of a neutron star for this theory. The results show that phase changes express themselves in this relation. Also, the radius of the most massive neutron stars is found to vary very little, which would make radius determinations much simpler if this would also be true in QCD.

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O. Hajizadeh and A. Maas
Fri, 23 Sep 16
5/50

Comments: 7 pages, 4 figures. poster presented at the “XXXIV International Symposium on Lattice Field Theory”, July 2016, Southampton, UK

Lattice QCD for Cosmology [CL]

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http://arxiv.org/abs/1606.07494


We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to several tens of MeV we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (chi) up to the few GeV temperature region. These two results, EoS and chi, can be used to predict the dark matter axion’s mass in the post-inflation scenario and/or give the relationship between the axion’s mass and the universal axionic angle, which acts as a initial condition of our universe.

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S. Borsanyi, Z. Fodor, K. Kampert, et. al.
Wed, 29 Jun 16
47/60

Comments: pdflatex, 40 figures; Section on experimental setups added, small corrections

On the compatibility of thermodynamic equilibrium conditions with the non-perturbative lattice propagators [CL]

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http://arxiv.org/abs/1606.02271


In this paper it is analyzed the compatibility of the non-perturbative equations of state of quarks and gluons arising from the lattice with some natural requirements for self gravitating objects at equilibrium: the existence of an equation of state (namely, the possibility to define the pressure as a function of the energy density), the absence of superluminal propagation and Le Chatelier’s principle. It is discussed under which conditions it is possible to extract an equation of state (in the above sense) from the non-perturbative propagators arising from the fits of the last lattice data. In particular, in the quarks case, there is a small but non vanishing range of temperatures in which it is not possible to define a single-valued functional relation between density and pressure. Interestingly enough, a small change of the parameters appearing in the fit of the lattice quark propagator (of around 10\%) can guarantee the fulfillment of all the three conditions (keeping alive, at the same time, the violation of positivity of the spectral representation which is the expected signal of confinement). As far as gluons are concerned, the analysis shows very similar results. These results can be very relevant in applications. For instance, in astrophysics, Rhoades and Ruffini were able to give an upper bound the maximal possible mass of a neutron star just using the three mentioned conditions. Thus, whether or not the non-perturbative quark and gluon propagators satisfy these conditions can have a strong impact on the estimate of the maximal mass of quark stars.

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F. Canfora, A. Giacomini, P. Pais, et. al.
Wed, 8 Jun 16
26/45

Comments: 22 pages, 16 figures

Equation of state of imbalanced cold matter from chiral perturbation theory [CL]

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http://arxiv.org/abs/1602.01317


We study the thermodynamic properties of matter at vanishing temperature for non-extreme values of the isospin chemical potential and of the strange quark chemical potential. From the leading order pressure obtained by maximizing the static chiral Lagrangian density we derive a simple expression for the equation of state in the pion condensed phase and in the kaon condensed phase. We find an analytical expression for the maximum of the ratio between the chiral perturbation energy density and the Stefan-Boltzmann energy density as well as for the isospin chemical potential at the peak in good agreement with lattice simulations of quantum chromodynamics. We speculate on the location of the crossover from the Bose-Einstein condensate state to the Bardeen-Cooper-Schrieffer state by a simple analysis of the thermodynamic properties of the system. For $\mu_I \gtrsim 2 m_\pi$ the leading order chiral perturbation theory breaks down; as an example it underestimates the energy density of the system and leads to a wrong asymptotic behavior.

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S. Carignano, A. Mammarella and M. Mannarelli
Thu, 4 Feb 16
11/50

Comments: 6 pages, 4 figures

Gravitational waves from cosmological first order phase transitions [CL]

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http://arxiv.org/abs/1511.04527


First order phase transitions in the early Universe generate gravitational waves, which may be observable in future space-based gravitational wave observatiories, e.g. the European eLISA satellite constellation. The gravitational waves provide an unprecedented direct view of the Universe at the time of their creation. We study the generation of the gravitational waves during a first order phase transition using large-scale simulations of a model consisting of relativistic fluid and an order parameter field. We observe that the dominant source of gravitational waves is the sound generated by the transition, resulting in considerably stronger radiation than earlier calculations have indicated.

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M. Hindmarsh, S. Huber, K. Rummukainen, et. al.
Tue, 17 Nov 15
79/87

Comments: Presented at the 33rd International Symposium on Lattice Field Theory, 14-18 July 2015, Kobe, Japan

The Standard Model cross-over on the lattice [CL]

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http://arxiv.org/abs/1508.07161


With the physical Higgs mass the Standard Model symmetry restoration phase transition is a smooth cross-over. We study the thermodynamics of the cross-over using numerical lattice Monte Carlo simulations of an effective SU(2) X U(1) gauge + Higgs theory, significantly improving on previously published results. We measure the Higgs field expectation value, thermodynamic quantities like pressure, energy density, speed of sound and heat capacity, and screening masses associated with the Higgs and Z fields. While the cross-over is smooth, it is very well defined with a width of only approximately 5 GeV. We measure the cross-over temperature from the maximum of the susceptibility of the Higgs condensate, with the result $T_c = 159.5 \pm 1.5$ GeV. Outside of the narrow cross-over region the perturbative results agree well with non-perturbative ones.

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M. DOnofrio and K. Rummukainen
Mon, 31 Aug 15
61/63

Comments: 10 pages

Latfield2: A c++ library for classical lattice field theory [CL]

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http://arxiv.org/abs/1508.05610


latfield2 is a C++ library designed to simplify writing parallel codes for solving partial differen- tial equations, developed for application to classical field theories in particle physics and cosmology. It is a significant rewrite of the latfield framework, moving from a slab domain decomposition to a rod decomposition, where the last two dimension of the lattice are scattered into a two dimensional process grid. Parallelism is implemented using the Message Passing Interface (MPI) standard, and hidden in the basic objects of grid-based simulations: Lattice, Site and Field. It comes with an integrated parallel fast Fourier transform, and I/O server class permitting computation to continue during the writing of large files to disk. latfield2 has been used for production runs on tens of thousands of processor elements, and is expected to be scalable to hundreds of thousands.

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D. David, M. Hindmarsh and N. Bevis
Tue, 25 Aug 15
22/69

Comments: 14 pages, 5 figures

Lattice Calculation of the Decay of Primordial Higgs Condensate [CEA]

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http://arxiv.org/abs/1506.06895


We study the resonant decay of the primordial Standard Model Higgs condensate after inflation into $SU(2)$ gauge bosons on the lattice. We find that the non-Abelian interactions between the gauge bosons quickly extend the momentum distribution towards high values, efficiently destroying the condensate after the onset of backreaction. For the inflationary scale $H = 10^8$ GeV, we find that 90% of the Higgs condensate has decayed after $n \sim 10$ oscillation cycles. This differs significantly from the Abelian case where, given the same couplings strengths, most of the condensate would persist after the resonance.

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K. Enqvist, S. Nurmi, S. Rusak, et. al.
Wed, 24 Jun 15
3/54

Comments: 16 pages, 6 figures

Precision determination of the pion-nucleon $σ$-term from Roy-Steiner equations [CL]

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http://arxiv.org/abs/1506.04142


We present a determination of the pion-nucleon ($\pi N$) $\sigma$-term $\sigma_{\pi N}$ based on the Cheng-Dashen low-energy theorem (LET), taking advantage of the recent precision data from pionic atoms to pin down the threshold $\pi N$ amplitude as well as of constraints from analyticity, unitarity, and crossing symmetry in the form of Roy-Steiner equations to perform the extrapolation to the Cheng-Dashen point in a reliable manner. With isospin-violating corrections included both in the scattering lengths and the LET, we obtain $\sigma_{\pi N}=(59.1\pm 1.9\pm 3.0)$ MeV $=(59.1\pm 3.5)$ MeV, where the first error refers to uncertainties in the $\pi N$ amplitude and the second to the LET. Consequences for the scalar nucleon couplings relevant for the direct detection of dark matter are discussed.

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M. Hoferichter, J. Elvira, B. Kubis, et. al.
Wed, 17 Jun 15
19/47

Comments: 5 pages, 1 figure

Lattice QCD input for axion cosmology [CL]

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http://arxiv.org/abs/1505.07455


One intriguing BSM particle is the QCD axion, which could simultaneously provide a solution to the Strong CP problem and account for some, if not all, of the dark matter density in the universe. This particle is a pNGB of the conjectured Peccei-Quinn (PQ) symmetry of the Standard Model. Its mass and interactions are suppressed by a heavy symmetry breaking scale, $f_a$, whose value is roughly greater than $10^{9}$ GeV (or, conversely, the axion mass, $m_a$, is roughly less than $10^4\ \mu \text{eV}$). The density of axions in the universe, which cannot exceed the relic dark matter density and is a quantity of great interest in axion experiments like ADMX, is a result of the early-universe interplay between cosmological evolution and the axion mass as a function of temperature. The latter quantity is proportional to the second derivative of the QCD free energy with respect to the CP-violating phase, $\theta$. However, this quantity is generically non-perturbative and previous calculations have only employed instanton models at the high temperatures of interest (roughly 1 GeV). In this and future works, we aim to calculate the temperature-dependent axion mass at small $\theta$ from first-principle lattice calculations, with controlled statistical and systematic errors. Once calculated, this temperature-dependent axion mass is input for the classical evolution equations of the axion density of the universe. Due to a variety of lattice systematic effects at the very high temperatures required, we perform a calculation of the leading small-$\theta$ cumulant of the theta vacua on large volume lattices for SU(3) Yang-Mills with high statistics as a first proof of concept, before attempting a full QCD calculation in the future. From these pure glue results, the misalignment mechanism yields the axion mass bound $m_a \geq (14.6\pm0.1) \ \mu \text{eV}$ when PQ-breaking occurs after inflation.

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E. Berkowitz, M. Buchoff and E. Rinaldi
Fri, 29 May 15
15/68

Comments: 26 pages, 9 figures

Improving cosmic string network simulations [CL]

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http://arxiv.org/abs/1406.1688


In real-time lattice simulations of cosmic strings in the Abelian Higgs model, the broken translational invariance introduces lattice artefacts; relativistic strings therefore decelerate and radiate. We introduce two different methods to construct a moving string on the lattice, and study in detail the lattice effects on moving strings. We find that there are two types of lattice artefact: there is an effective maximum speed with which a moving string can be placed on the lattice, and a moving string also slows down, with the deceleration approximately proportional to the exponential of the velocity. To mitigate this, we introduce and study an improved discretisation, based on the tree-level L\”{u}scher-Weisz action, which is found to reduce the deceleration by an order of magnitude, and to increase the string speed limit by an amount equivalent to halving the lattice spacing. The improved algorithm is expected to be very useful for 3D simulations of cosmic strings in the early universe, where one wishes to simulate as large a volume as possible.

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M. Hindmarsh, K. Rummukainen, T. Tenkanen, et. al.
Mon, 9 Jun 14
11/40

Comments: 13 pages, 10 figures

QCD and strongly coupled gauge theories: challenges and perspectives [CL]

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http://arxiv.org/abs/1404.3723


We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly-coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

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N. Brambilla, S. Eidelman, P. Foka, et. al.
Wed, 16 Apr 14
32/52

The Sphaleron Rate in the Minimal Standard Model [CL]

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http://arxiv.org/abs/1404.3565


We use large-scale lattice simulations to compute the rate of baryon number violating processes (the sphaleron rate), the Higgs field expectation value, and the critical temperature in the Standard Model across the electroweak phase transition temperature. While there is no true phase transition between the high-temperature symmetric phase and the low-temperature broken phase, the cross-over is sharply defined at $T_c = (159\pm 1)$\,GeV. The sphaleron rate in the symmetric phase ($T> T_c$) is $\Gamma/T^4 = (18\pm 3)\alpha_W^5$, and in the broken phase in the physically interesting temperature range $130\mbox{\,GeV} < T < T_c$ it can be parametrized as $\log(\Gamma/T^4) = (0.83\pm 0.01)T/{\rm GeV} – (147.7\pm 1.9)$. The freeze-out temperature in the early Universe, where the Hubble rate wins over the baryon number violation rate, is $T_* = (131.7\pm 2.3)$\,GeV. These values, beyond being intrinsic properties of the Standard Model, are relevant for e.g. low-scale leptogenesis scenarios.

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M. DOnofrio, K. Rummukainen and A. Tranberg
Tue, 15 Apr 14
67/73

Planning the Future of U.S. Particle Physics (Snowmass 2013): Chapter 1: Summary [CL]

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http://arxiv.org/abs/1401.6075


These reports present the results of the 2013 Community Summer Study of the APS Division of Particles and Fields (“Snowmass 2013”) on the future program of particle physics in the U.S. Chapter 1 contains the Executive Summary and the summaries of the reports of the nine working groups.

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Fri, 24 Jan 14
37/57

LIFE ON EARTH — AN ACCIDENT? Chiral Symmetry and the Anthropic Principle [CL]

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http://arxiv.org/abs/1312.7550


I discuss the fine-tuning of the nuclear forces and in the formation of nuclei in the production of the elements in the Big Bang and in stars.

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Tue, 31 Dec 13
25/49

Accurate evaluation of hadronic uncertainties in spin-independent WIMP-nucleon scattering: Disentangling two- and three-flavor effects [CL]

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http://arxiv.org/abs/1312.4951


We show how to avoid unnecessary and uncontrolled assumptions usually made in the literature about soft SU(3) flavor symmetry breaking in determining the two-flavor nucleon matrix elements relevant for direct detection of WIMPs. Based on SU(2) Chiral Perturbation Theory, we provide expressions for the proton and neutron scalar couplings $f_u^{p,n}$ and $f_d^{p,n}$ with the pion-nucleon sigma-term as the only free parameter, which should be used in the analysis of direct detection experiments. This approach for the first time allows for an accurate assessment of hadronic uncertainties in spin-independent WIMP-nucleon scattering and for a reliable calculation of isospin-violating effects. We find that the traditional determinations of $f_u^p-f_u^n$ and $f_d^p-f_d^n$ are off by a factor of 2.

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Thu, 19 Dec 13
58/76