Tag Archives: Other Condensed Matter

Domain wall annihilation — a QFT perspective [CL]

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http://arxiv.org/abs/2212.11204


Domain wall networks in the early universe, formed upon spontaneous breaking of a discrete symmetry, have a rich impact on cosmology. Yet, they remain somewhat unexplored. We introduce a new analytic strategy to understand better the domain wall epoch, from formation to annihilation. Our method includes a quantum field theoretical treatment of the initial state at domain wall formation, as well as of the time evolution. We find that the domain wall area density for a network with biased initial condition in $d+1$ dimensional flat spacetime evolves as $t^{-1/2}\,\exp\big(- (t/t_{ann})^{d/2}\big)$. We comment on the relation between this and previous results obtained in condensed matter and in cosmology. The extrapolation of this law to an expanding universe applies to networks that are close to the domain wall `gas’ limit.

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O. Pujolas and G. Zahariade
Thu, 22 Dec 22
43/59

Comments: 14 pages, 5 figures

Non-equilibrium dynamics of Axion-like particles: the quantum master equation [CEA]

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http://arxiv.org/abs/2212.05161


We study the non-equilibrium dynamics of Axion-like particles (ALP) coupled to Standard Model degrees of freedom in thermal equilibrium. The Quantum Master Equation (QME) for the (ALP) reduced density matrix is derived to leading order in the coupling of the (ALP) to the thermal bath, but to \emph{all} orders of the bath couplings to degrees of freedom within or beyond the Standard Model other than the (ALP). The (QME) describes the damped oscillation dynamics of an initial misaligned (ALP) condensate, thermalization with the bath, decoherence and entropy production within a unifying framework. The (ALP) energy density $\mathcal{E}(t)$ features two components: a cold'' component from the misaligned condensate and ahot” component from thermalization with the bath, with $\mathcal{E}(t)= \mathcal{E}{c}\,e^{-\gamma(T)\,t}+\mathcal{E}{h}(1-e^{-\gamma(T)\,t})$ thus providing a “mixed dark matter” scenario. Relaxation of the (ALP) condensate, thermalization, decoherence and entropy production occur on similar time scales. An explicit example with (ALP)-photon coupling, valid post recombination yields a relaxation rate $\gamma(T)$ with a substantial enhancement from thermal emission and absorption. A misaligned condensate is decaying at least since recombination and on the same time scale thermalizing with the cosmic microwave background (CMB). Possible consequences for birefringence of the (CMB) and (ALP) contribution to the effective number of ultrarelativistic species and galaxy formation are discussed.

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S. Cao and D. Boyanovsky
Tue, 13 Dec 22
67/105

Comments: 28 pages

Energetic Electron Irradiations of Amorphous and Crystalline Sulphur-Bearing Astrochemical Ices [CL]

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http://arxiv.org/abs/2210.01119


Laboratory experiments have confirmed that the radiolytic decay rate of astrochemical ice analogues is dependent upon the solid phase of the target ice, with some crystalline molecular ices being more radio-resistant than their amorphous counterparts. The degree of radio-resistance exhibited by crystalline ice phases is dependent upon the nature, strength, and extent of the intermolecular interactions that characterise their solid structure. For example, it has been shown that crystalline CH3OH decays at a significantly slower rate when irradiated by 2 keV electrons at 20 K than does the amorphous phase due to the stabilising effect imparted by the presence of an extensive array of strong hydrogen bonds. These results have important consequences for the astrochemistry of interstellar ices and outer Solar System bodies, as they imply that the chemical products arising from the irradiation of amorphous ices (which may include prebiotic molecules relevant to biology) should be more abundant than those arising from similar irradiations of crystalline phases. In this present study, we have extended our work on this subject by performing comparative energetic electron irradiations of the amorphous and crystalline phases of the sulphur-bearing molecules H2S and SO2 at 20 K. We have found evidence for phase-dependent chemistry in both these species, with the radiation-induced exponential decay of amorphous H2S being more rapid than that of the crystalline phase, similar to the effect that has been previously observed for CH3OH. For SO2, two fluence regimes are apparent: a low-fluence regime in which the crystalline ice exhibits a rapid exponential decay while the amorphous ice possibly resists decay, and a high-fluence regime in which both phases undergo slow exponential-like decays.

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D. Mifsud, P. Herczku, R. Rácz, et. al.
Wed, 5 Oct 22
40/73

Comments: Published in Frontiers in Chemistry (open access)

Vortex Pinning in Neutron Stars, Slip-stick Dynamics, and the Origin of Spin Glitches [HEAP]

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http://arxiv.org/abs/2208.11494


We study pinning and unpinning of superfluid vortices in the inner crust of a neutron star using 3-dimensional dynamical simulations. Strong pinning occurs for certain lattice orientations of an idealized, body-centered cubic lattice, and occurs generally in an amorphous or impure nuclear lattice. The pinning force per unit length is $\sim 10^{16}$ dyn cm$^{-1}$ for a vortex-nucleus interaction that is repulsive, and $\sim 10^{17}$ dyn cm$^{-1}$ for an attractive interaction. The pinning force is strong enough to account for observed spin jumps (glitches). Vortices forced through the lattice move with a slip-stick character; for a range of superfluid velocities, the vortex can be in either a cold, pinned state or a hot unpinned state, with strong excitation of Kelvin waves on the vortex. This two-state nature of vortex motion sets the stage for large-scale vortex movement that creates an observable spin glitch. We argue that the vortex array is likely to become tangled as a result of repeated unpinnings and repinnings. We conjecture that during a glitch, the Kelvin-wave excitation spreads rapidly along the direction of the mean superfluid vorticity and slower in the direction perpendicular to it, akin to an anisotropic deflagration.

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B. Link and Y. Levin
Thu, 25 Aug 22
23/43

Comments: 12 pages, 7 figures (two animations)

Why not Neutrinos as the Dark Matter? A Critical Review, KATRIN and New Research Directions [CL]

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http://arxiv.org/abs/2208.06460


We challenge the traditional wisdom that cosmological (big bang relic) neutrinos can only be hot Dark Matter. We provide a critical review of the concepts, derivations and arguments in foundational books and recent publications that led respected researchers to proclaim that “[Dark Matter] cannot be neutrinos”. We then provide the physics resulting in relic neutrino’s significant power loss from the interaction of its anomalous magnetic moment with a high-intensity primordial magnetic fields, resulting in subsequent condensation into Condensed Neutrino Objects (CNOs). Finally, the experimental degenerate mass bounds that would rule out condensed cosmological neutrinos as the Dark Matter (unless there is new physics that would require a modification to the CNO Equation of State) are provided. We conclude with a discussion on new directions for research.

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D. Buettner and P. Morley
Tue, 16 Aug 22
23/74

Comments: 20 pages, 6 figures, 7th Symposium on Neutrinos and Dark Matter in Nuclear Physics (NDM22)

Comparative Electron Irradiations of Amorphous and Crystalline Astrophysical Ice Analogues [GA]

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http://arxiv.org/abs/2204.13701


Laboratory studies of the radiation chemistry occurring in astrophysical ices have demonstrated the dependence of this chemistry on a number of experimental parameters. One experimental parameter which has received significantly less attention is that of the phase of the solid ice under investigation. In this present study, we have performed systematic 2 keV electron irradiations of the amorphous and crystalline phases of pure CH3OH and N2O astrophysical ice analogues. Radiation-induced decay of these ices and the concomitant formation of products were monitored in situ using FT-IR spectroscopy. A direct comparison between the irradiated amorphous and crystalline CH3OH ices revealed a more rapid decay of the former compared to the latter. Interestingly, a significantly lesser difference was observed when comparing the decay rates of the amorphous and crystalline N2O ices. These observations have been rationalised in terms of the strength and extent of the intermolecular forces present in each ice. The strong and extensive hydrogen-bonding network that exists in crystalline CH3OH (but not in the amorphous phase) is suggested to significantly stabilise this phase against radiation-induced decay. Conversely, although alignment of the dipole moment of N2O is anticipated to be more extensive in the crystalline structure, its weak attractive potential does not significantly stabilise the crystalline phase against radiation-induced decay, hence explaining the smaller difference in decay rates between the amorphous and crystalline phases of N2O compared to those of CH3OH. Our results are relevant to the astrochemistry of interstellar ices and icy Solar System objects, which may experience phase changes due to thermally-induced crystallisation or space radiation-induced amorphisation.

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D. Mifsud, P. Hailey, P. Herczku, et. al.
Mon, 2 May 22
4/52

Comments: Manuscript contains 18 pages, 6 figures, and 2 tables. Published as an advance article in PCCP

Spin precession in the gravity wave analogue black hole spacetime [CL]

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http://arxiv.org/abs/2203.11459


It was predicted that the spin precession frequency of a stationary gyroscope shows various anomalies in the strong gravity regime if its orbit shrinks, and eventually its precession frequency becomes arbitrarily high very close to the horizon of a rotating black hole. Considering the gravity waves of a flowing fluid with vortex in a shallow basin, that acts as a rotating analogue black hole, one can observe the predicted strong gravity effect on the spin precession in the laboratory. Attaching a thread with the buoyant particles and anchored it to the bottom of the fluid container with a short length of miniature chain, one can construct a simple local test gyroscope to measure the spin precession frequency in the vicinity of the gravity wave analogue black hole. The thread acts as the axis of the gyroscope. By regulating the orbital frequency of the test gyroscope, one can also be able to measure the strong gravity Lense-Thirring effect and geodetic/de-Sitter effect with this experimental set-up, as the special cases. For example, to measure the Lense-Thirring effect, the length of the miniature chain can be set to zero, so that the gyroscope becomes static. One can also measure the geodetic precession with this system by orbiting the test gyroscope in the so-called Keplerian frequency around the non-rotating analogue black hole that can be constructed by making the rotation of the fluid/vortex negligible compared to its radial velocity.

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C. Chakraborty and B. Mukhopadhyay
Thu, 24 Mar 22
24/56

Comments: 12 pages including 4 figures; Version published in Universe

Gaia Reveals Dark Matter Correlations Across the Fornax Dwarf Spheroidal Galaxy: An Assessment of Dark Matter Models [GA]

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http://arxiv.org/abs/2203.01525


The predicted size of dark matter substructures in kilo-parsec scales is model-dependent. Therefore, if the correlations between dark matter mass densities, as a function of the distances between them, are measured via observations, we can scrutinize dark matter scenarios. In this paper, we use Gaia’s data to infer the single-body phase-space density of the stars in the Fornax dwarf spheroidal galaxy. The latter together with the Jeans equation, after eliminating the gravitational potential using the Poisson equation, reveals the mass density of dark matter as a function of its position in the galaxy. We derive the correlations between dark matter mass densities as a function of distances between them. For distances beyond 100 parsec, no statistically significant correlation is observed. We use the results to limit the parameter space of the Ginzburg-Landau statistical field theory of dark matter mass densities, and subsequently shrink the parameter space of (i) a classic gas dark matter and (ii) a superfluid dark matter. Our results can be used to leave bounds on high-resolution N-body simulations by comparing the correlations computed using their outputs and the measured ones via observations.

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A. Borzou
Fri, 4 Mar 22
28/63

Comments: 11 pages, 6 figures

Nuclear Shell Structure in a Finite-Temperature Relativistic Framework [CL]

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http://arxiv.org/abs/2110.05749


The shell evolution of neutron-rich nuclei with temperature is studied in a beyond-mean-field framework rooted in the meson-nucleon Lagrangian. The temperature-dependent Dyson equation with the dynamical kernel taking into account the particle-vibration coupling (PVC) is solved for the fermionic propagators in the basis of the thermal relativistic mean-field Dirac spinors. The calculations are performed for $^{68-78}$Ni in a broad range of temperatures $0 \leq T \leq 4$ MeV. The special focus is put on the fragmentation pattern of the single-particle states, which is further investigated within toy models in strongly truncated model spaces. Such models allow for quantifying the sensitivity of the fragmentation to the phonon frequencies, the PVC strength and to the mean-field level density. The model studies provide insights into the temperature evolution of the PVC mechanism in real nuclear systems under the conditions which may occur in astrophysical environments.

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H. Wibowo and E. Litvinova
Wed, 13 Oct 21
71/80

Comments: Article: 17 pages, 19 figures

Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs [SSA]

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http://arxiv.org/abs/2108.11389


Do white dwarfs have inner cores made of iron? Neutron rich nuclei like $^{56}$Fe experience a net gravitational force and sediment toward the core. Using new phase diagrams and molecular dynamics simulations, we show that $^{56}$Fe should separate into mesoscopic Fe-rich crystallites due to its large charge relative to the background. At solar abundances, these crystallites rapidly precipitate and form an inner core of order 100 km and $10^{-3} M_\odot$ that may be detectable with asteroseismology. Associated cooling delays could be up to a Gyr for low mass white dwarfs but are only $\sim$0.1 Gyr for massive white dwarfs, so while this mechanism may contribute to the Q-branch the heating is insufficient to fully explain it.

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M. Caplan, I. Freeman, C. Horowitz, et. al.
Fri, 27 Aug 21
60/67

Comments: 8 pages, 5 figures, accepted for publication in ApJ Letters

Kibble mechanism for electroweak magnetic monopoles and magnetic fields [CL]

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http://arxiv.org/abs/2108.05357


We develop topological criteria for the existence of electroweak magnetic monopoles and Z-strings and extend the Kibble mechanism to study their formation during the electroweak phase transition. The distribution of magnetic monopoles produces magnetic fields that have a spectrum $B_\lambda \propto \lambda^{-2}$ where $\lambda$ is a smearing length scale. Even as the magnetic monopoles annihilate due to the confining Z-strings, the magnetic field evolves with the turbulent plasma and may be relevant for cosmological observations.

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T. Patel and T. Vachaspati
Fri, 13 Aug 21
6/64

Comments: 6 pages; 4 figures

Prototype Superfluid Gravitational Wave Detector [CL]

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http://arxiv.org/abs/2107.00120


We study a cross-shaped cavity filled with superfluid $^4$He as a prototype resonant-mass gravitational wave detector. Using a membrane and a re-entrant microwave cavity as a sensitive optomechanical transducer, we were able to observe the thermally excited high-$Q$ acoustic modes of the helium at 20 mK temperature and achieved a strain sensitivity of $8 \times 10^{-19}$ Hz$^{-1/2}$ to gravitational waves. To facilitate the broadband detection of continuous gravitational waves, we tune the kilohertz-scale mechanical resonance frequencies up to 173 Hz/bar by pressurizing the helium. With reasonable improvements, this architecture will enable the search for GWs in the 1-30 kHz range, relevant for a number of astrophysical sources both within and beyond the Standard Model.

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V. Vadakkumbatt, M. Hirschel, J. Manley, et. al.
Fri, 2 Jul 21
44/67

Comments: 8 pages, 7 figures

Nonclassicality of axion-like dark matter through gravitational self-interactions [CEA]

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http://arxiv.org/abs/2105.13451


Axion-like particles (ALPs) are promising dark matter candidates. A classical field description is typically employed, motivated by large phase space occupation numbers. Here we show that such a description is accompanied by a quantum effect: squeezing due to gravitational self-interactions. For a typical QCD axion today, the onset of squeezing is reached on microsecond-scales and grows over millennia. Thus within the usual models based on the classical Schr\”odinger-Poisson equation, a type of Gross-Pitaevskii equation, any viable ALP is nonclassical. We also show that squeezing may be relevant on scales of axion haloscopes, or within galactic solitonic cores. Conversely, our results highlight the incompleteness and limitations of the typically employed classical single field description of ALPs.

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M. Kopp, V. Fragkos and I. Pikovski
Mon, 31 May 21
68/72

Comments: 10 pages, 3 figures

The FAST Galactic Plane Pulsar Snapshot survey: I. Project design and pulsar discoveries [HEAP]

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http://arxiv.org/abs/2105.08460


Discovery of pulsars is one of the main goals for large radio telescopes. The Five-hundred-meter Aperture Spherical radio Telescope (FAST), that incorporates an L-band 19-beam receiver with a system temperature of about 20~K, is the most sensitive radio telescope utilized for discovering pulsars. We designed the {\it snapshot} observation mode for a FAST key science project, the Galactic Plane Pulsar Snapshot (GPPS) survey, in which every four nearby pointings can observe {\it a cover} of a sky patch of 0.1575 square degrees through beam-switching of the L-band 19-beam receiver. The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes. The goal of the GPPS survey is to discover pulsars within the Galactic latitude of $\pm10^{\circ}$ from the Galactic plane, and the highest priority is given to the inner Galaxy within $\pm5^{\circ}$. Up to now, the GPPS survey has discovered 201 pulsars, including currently the faintest pulsars which cannot be detected by other telescopes, pulsars with extremely high dispersion measures (DMs) which challenge the currently widely used models for the Galactic electron density distribution, pulsars coincident with supernova remnants, 40 millisecond pulsars, 16 binary pulsars, some nulling and mode-changing pulsars and rotating radio transients (RRATs). The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars. Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars. The GPPS survey discoveries are published and will be updated at this http URL .

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J. Han, C. Wang, P. Wang, et. al.
Wed, 19 May 21
27/64

Comments: 38 pages, 22 figures. See this http URL for News and Views

Cosmological Geometric Phase From Pure Quantum States: A study without/with having Bell's inequality violation [CL]

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http://arxiv.org/abs/2105.06254


In this paper, using the concept of Lewis Riesenfeld invariant quantum operator method for finding continuous eigenvalues of quantum mechanical wave functions we derive the analytical expressions for the cosmological geometric phase, which is commonly identified to be the Pancharatnam Berry phase from primordial cosmological perturbation scenario. We compute this cosmological geometric phase from two possible physical situations,(1) In the absence of Bell’s inequality violation and (2) In the presence of Bell’s inequality violation having the contributions in the sub Hubble region ($-k\tau\gg 1$), super Hubble region ($-k\tau\ll 1$) and at the horizon crossing point ($-k\tau= 1$) for massless field ($m/{\cal H}\ll 1$), partially massless field ($m/{\cal H}\sim 1$) and massive/heavy field ($m/{\cal H}\gg 1$), in the background of quantum field theory of spatially flat quasi De Sitter geometry. The prime motivation for this work is to investigate the various unknown quantum mechanical features of primordial universe. To give the realistic interpretation of the derived theoretical results we express everything initially in terms of slowly varying conformal time dependent parameters, and then to connect with cosmological observation we further express the results in terms of cosmological observables, which are spectral index/tilt of scalar mode power spectrum ($n_{\zeta}$) and tensor-to-scalar ratio ($r$). Finally, this identification helps us to provide the stringent numerical constraints on the Pancharatnam Berry phase, which confronts well with recent cosmological observation.

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S. Choudhury
Mon, 17 May 21
52/55

Comments: 130 pages, 20 figures, 1 table

Tully-Fisher relation and its connection to a novel approach to general relativity [CL]

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http://arxiv.org/abs/2101.07763


The flattening of galaxy rotation curves in the weak gravity regime has been the center of scientific debate for decades. The cold dark matter ($\rm CDM$) paradigm has been posited as the standard explanation, where the mass of the dark halo $m(r) = r/Gn$ roughly increases linearly with radial distance at large distances where $G$ the gravitational constant and $n$ a dimensionless parameter which depends on the amount of baryonic matter $M$ within the galaxy. Despite numerous advances in modeling galaxy formation and evolution within the dark energy-cold dark matter ($\Lambda{\rm CDM}$) model in cosmology, a scientific consensus on the origin of the observed dependence of the dimensionless parameter $n = (GMa_{0})^{-1/2}$ on the mass of baryonic matter $M$ within the galaxy (the Tully-Fisher relation), and the connection of the cosmological constant $\Lambda$ to the acceleration parameter $a_{0} \sim (\Lambda/3)^{1/2}$ remains elusive. Here, we propose relativistic equations of gravity ($\nabla_{\nu}\mathcal{K}^{\nu}{\,\,\mu} = 8\pi GM\Psi^{*}\mathcal{D}{\mu}\Psi$, where $\mathcal{K}{\mu\nu}$ is a Hermitian tensor, $\mathcal{D}{\mu}$ a covariant derivative and $\Psi$ is a complex-valued function) which we show to not only contain Einstein Field Equations but also satisfy the Tully-Fisher relation. In the weak field limit, the gravity equations reduce to a theory of $n$ bosons (Ginzburg Landau theory) where the order parameter $\Psi$ is normalized as $\int_{0}^{1/a_{0}} dr\,4\pi r^2\Psi^*\Psi = n$ and $1/a_{0} \sim (\Lambda/3)^{-1/2}$ is the cut-off radius comparable to the size of the de Sitter universe. Our investigations have significant implications for the dark matter versus MOdified Newtonian Dynamics (MOND) debate, since we provide a framework where the Tully-Fisher relation in galaxies is satisfied within the context of Einstein’s general relativity.

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G. Kanyolo and T. Masese
Wed, 20 Jan 21
27/61

Comments: 9 pages, 1 figure

Directional detection of light dark matter from three-phonon events in superfluid $^4$He [CL]

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http://arxiv.org/abs/2012.01432


We present the analysis of a new signature for light dark matter detection with superfluid $^4$He: the emission of three phonons. We show that, in a region of mass below the MeV, the kinematics of this process can offer a way to reconstruct the dark matter interaction vertex, while providing background rejection via coincidence requirements and directionality. We develop all the necessary technology to deal with such an observable, and compute the associated differential distributions.

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A. Caputo, A. Esposito, F. Piccinini, et. al.
Fri, 4 Dec 20
70/77

Comments: 8 pages, 4 figures

Searching for low mass dark matter via phonon creation in superfluid 4He [CL]

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http://arxiv.org/abs/2005.08824


We consider the scattering of dark matter particles from superfluid liquid $^4$He, which has been proposed as a target for their direct detection. Focusing on dark matter masses below ~1 MeV, we demonstrate from sum-rule arguments that for momentum transfers of interest the dominant process is the creation of a single phonon, with the direct creation of two or more phonons much less likely. We show further that the anomalous dispersion of phonons in liquid $^4$He at low pressures [i.e., $d^2\omega (q)/dq^2 > 0$, where $q$ and $\omega(q)$ are the phonon momentum and energy] has the important consequence that a single phonon will decay over a relatively short distance into a shower of lower energy phonons centered on the direction of the original phonon. Thus the experimental challenge in this regime is to detect a shower of low energy phonons, not just a single phonon. Additional information from the distribution of phonons in such a shower could enhance the determination of the dark matter mass.

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G. Baym, D. Beck, J. Filippini, et. al.
Tue, 19 May 20
55/92

Comments: 17 pages, 12 figures

Dense Matter and Neutron Stars: Some Basic Notions [CL]

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http://arxiv.org/abs/1912.11876


A number of properties of dense matter can be understood semiquantitatively in terms of simple physical arguments. We begin with the outer parts of neutron stars, and consider the density at which pressure ionization occurs, the density at which electrons become relativistic, the density at which neutrons drip out of nuclei, and the size of the equilibrium nucleus in dense matter. Subsequently, we treat the so-called “pasta” phases expected to occur at densities just below the density at which the transition from the crust to the liquid core of a neutron star occurs. We then consider aspects of superfluidity in dense matter. Estimates of pairing gaps in homogeneous nuclear matter are given, and the effect of the dense medium on the interaction between nucleons is described. Finally, we turn to superfluidity in the crust of neutron stars and especially the neutron superfluid density, an important quantity in the theory of sudden speedups of the rotation rate of some pulsars.

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C. Pethick
Mon, 30 Dec 19
40/51

Comments: 19 pages, 1 figure. Lectures presented at the LIX Cracow School of Theoretical Physics, Zakopane, Poland, June 14-22, 2019

Dense Matter and Neutron Stars: Some Basic Notions [CL]

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http://arxiv.org/abs/1912.11876


A number of properties of dense matter can be understood semiquantitatively in terms of simple physical arguments. We begin with the outer parts of neutron stars, and consider the density at which pressure ionization occurs, the density at which electrons become relativistic, the density at which neutrons drip out of nuclei, and the size of the equilibrium nucleus in dense matter. Subsequently, we treat the so-called “pasta” phases expected to occur at densities just below the density at which the transition from the crust to the liquid core of a neutron star occurs. We then consider aspects of superfluidity in dense matter. Estimates of pairing gaps in homogeneous nuclear matter are given, and the effect of the dense medium on the interaction between nucleons is described. Finally, we turn to superfluidity in the crust of neutron stars and especially the neutron superfluid density, an important quantity in the theory of sudden speedups of the rotation rate of some pulsars.

Read this paper on arXiv…

C. Pethick
Mon, 30 Dec 19
7/51

Comments: 19 pages, 1 figure. Lectures presented at the LIX Cracow School of Theoretical Physics, Zakopane, Poland, June 14-22, 2019

Unconventional phase III of high-pressure solid hydrogen [CL]

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http://arxiv.org/abs/1906.10854


We reassess the phase diagram of high-pressure solid hydrogen using mean-filed and many-body wave function based approaches to determine the nature of phase III of solid hydrogen. To discover the best candidates for the phase III, Density Functional Theory with meta-generalized-gradient approximation (meta-GGA) non-empirical strongly constrained and appropriately normed (SCAN) exchange-correlation (XC) is employed. We study eleven molecular structures with different symmetry, which are the most competitive phases, within the pressure range of 100 to 500 GPa. The SCAN phase diagram predicts that the $C2/c-24$ and $P6_122-36$ structures are the best candidates for the phase III with energy difference of less than 1 meV/atom. To verify the stability of the competitive insulator structures of $C2/c-24$ and $P6_122-36$, we apply the diffusion quantum Monte Carlo (DMC) to optimise the percentage of the exact exchange ($\alpha$) in the trial many-body wave function. We found that the optimised $\alpha$ equals to $40 \%$, and the corresponding XC functional is named PBE${1x}$. The energy gain with respect to the conventional hybrid functional (PBE$_0$) with $\alpha = 25\%$ varies with density and structure. The PBE${1x}$-DMC enthalpy-pressure phase diagram predicts that the $P6_122-36$ structure is stable up to 210 GPa where it transforms to the $C2/c-24$. We predict that the phase III of high-pressure solid hydrogen is polymorphic.

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S. Azadi and T. Kuehne
Thu, 27 Jun 19
62/62

Comments: N/A

Formation of topological vortices during superfluid transition in a rotating vessel [CL]

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http://arxiv.org/abs/1805.09377


Formation of topological defects during symmetry breaking phase transitions via the {\it Kibble mechanism} is extensively used in systems ranging from condensed matter physics to the early stages of the universe. Kibble mechanism uses topological arguments and predicts equal probabilities for the formation of defects and anti-defects. Certain situations, however, require a net bias in the production of defects (or antidefects) during the transition, for example, superfluid transition in a rotating vessel, or flux tubes formation in a superconducting transition in the presence of external magnetic field. In this paper we present a modified Kibble mechanism for a specific system, $^4$He superfluid transition in a rotating vessel, which can produce the required bias of vortices over antivortices. Our results make distinctive predictions which can be tested in superfluid $^4$He experiments. These results also have important implications for superfluid phase transitions in rotating neutron stars and also for any superfluid phases of QCD arising in the non-central low energy heavy-ion collision experiment due to an overall rotation.

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S. Dave and A. Srivastava
Wed, 30 May 18
14/65

Comments: 8 pages, 4 figures

Rapid crust coupling and glitch rises in superfluid neutron stars [HEAP]

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http://arxiv.org/abs/1804.02706


Pulsar glitches provide a unique way to study neutron star microphysics because short post-glitch timescales are directly linked to strong frictional processes on small scales. To illustrate the connection between macroscopic observables and microphysics, we calculate the mutual friction strength associated with Kelvin wave excitation for realistic microscopic parameters. These new density-dependent profiles are then combined with a simple three-component model to study the neutron star glitch rise. We find that the superfluid transfers angular momentum to different parts of the crust and then core during the first $30 \, $s after the onset of the glitch. This causes the spin frequency change to become non-monotonic in time, with a maximum value much larger than the measured glitch size, as well as a possible delay in recovery beyond $30 \, $s. We suggest that future telescopes, like the Square Kilometer Array, might be able to distinguish such coupling profiles and provide constraints on the complex small-scale physics.

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V. Graber, A. Cumming and N. Andersson
Tue, 10 Apr 18
7/79

Comments: 7 pages, 1 table, 3 figures, submitted to ApJL

The Photon in Dense Nuclear Matter I: Random Phase Approximation [HEAP]

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http://arxiv.org/abs/1712.05447


We present a comprehensive and pedagogic discussion of the properties of photons in cold and dense nuclear matter based on the resummed one-loop photon self energy. Correlations between electrons, muons, protons and neutrons in beta equilibrium that arise due to electromagnetic and strong interactions are consistently taken into account within the random phase approximation. Screening effects and damping as well as collective excitations are systematically studied in a fully relativistic setup. Our study is relevant to linear response theory of dense nuclear matter, calculations of transport properties of cold dense matter and to investigations of the production and propagation of hypothetical vector bosons such as the dark photons.

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S. Stetina, E. Rrapaj and S. Reddy
Mon, 18 Dec 17
41/49

Comments: N/A

The Gross-Pitaevskii equations of a static and spherically symmetric condensate of gravitons [CL]

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http://arxiv.org/abs/1711.01282


In this paper we consider the Dvali and G\’omez assumption that the end state of a gravitational collapse is a Bose-Einstein condensate of gravitons. We then construct the two Gross-Pitaevskii equations of a static and spherically symmetric configuration of the condensate.
These two equations correspond to the constrained minimisation of the gravitational Hamiltonian with respect to the redshift and the Newtonian potential, per given number of gravitons. We find that the effective geometry of the condensate is the one of a gravastar (a DeSitter star) with a sub-Planckian cosmological constant. Thus, the condensate is always quantum and weakly coupled, no matter its size.
Finally, applying our findings to the current observable Universe, we find that the emergent cosmological constant of the condensate, inversely proportional to the square of the visible mass, matches unexpectedly well the observational value.

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F. Cunillera and C. Germani
Tue, 7 Nov 17
56/118

Comments: 10 pages

Path integral Monte Carlo simulations of dense carbon-hydrogen plasmas [CL]

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http://arxiv.org/abs/1708.07246


Carbon-hydrogen plasmas and hydrocarbon materials are of broad interest to laser shock experimentalists, high energy density physicists, and astrophysicists. Accurate equations of state (EOS) of hydrocarbons are valuable for various studies from inertial confinement fusion (ICF) to planetary science. By combining path integral Monte Carlo (PIMC) results at high temperatures and density functional theory molecular dynamics (DFT-MD) results at lower temperatures, we compute the EOS for hydrocarbons at 1184 separate ($\rho,T$)-points distributed over a range of compositions. These methods accurately treat electronic excitation and many-body interaction effects and thus provide a benchmark-quality EOS that surpasses that of semi-empirical and Thomas-Fermi-based methods in the warm dense matter regime. By comparing our first-principles EOS to the LEOS 5112 model for CH, we validate the specific heat assumptions in this model but suggest that the Grueneisen parameter is too large at low temperature. Based on our first-principles EOS, we predict the Hugoniot curve of polystyrene to be ~5% stiffer at maximum compression than that predicted by orbital-free DFT and other Thomas-Fermi-based approaches. By investigating the atomic structure and chemical bonding, we show a drastic decrease in the lifetime of chemical bonds in the pressure interval of 0.4-4 megabar. We find the assumption of linear mixing to be valid for describing the EOS and the shock Hugoniot curve of the dense, partially ionized hydrocarbons under consideration. We make predictions of the shock compression of glow-discharge polymers and investigate the effects of oxygen content and C:H ratio on their Hugoniot curve. Our full suite of first-principles simulation results may be used to benchmark future theoretical investigations pertaining to hydrocarbon EOS, and should be helpful in guiding the design of future gigabar experiments.

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S. Zhang, B. Militzer, L. Benedict, et. al.
Fri, 25 Aug 17
30/59

Comments: 13 pages, 12 figures, 1 table

Laser induced fluorescence for axion dark matter detection: a feasibility study in YLiF$_4$:Er$^{3+}$ [CEA]

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http://arxiv.org/abs/1707.06103


We present a detection scheme to search for QCD axion dark matter, that is based on a direct interaction between axions and electrons explicitly predicted by DFSZ axion models. The local axion dark matter field shall drive transitions between Zeeman-split atomic levels separated by the axion rest mass energy $m_a c^2$. Axion-related excitations are then detected with an upconversion scheme involving a pump laser that converts the absorbed axion energy ($\sim $ hundreds of $\mu$eV) to visible or infrared photons, where single photon detection is an established technique. The proposed scheme involves rare-earth ions doped into solid-state crystalline materials, and the optical transitions take place between energy levels of $4f^N$ electron configuration. Beyond discussing theoretical aspects and requirements to achieve a cosmologically relevant sensitivity, especially in terms of spectroscopic material properties, we experimentally investigate backgrounds due to the pump laser at temperatures in the range $1.9-4.2$ K. Our results rule out excitation of the upper Zeeman component of the ground state by laser-related heating effects, and are of some help in optimizing activated material parameters to suppress the multiphonon-assisted Stokes fluorescence.

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C. Braggio, G. Carugno, F. Chiossi, et. al.
Thu, 20 Jul 17
24/56

Comments: 8 pages, 5 figures

Photonic Chiral Vortical Effect [CL]

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http://arxiv.org/abs/1702.08886


Circularly polarized photons have the Berry curvature in the semiclassical regime. Based on the kinetic equation for such chiral photons, we derive the (non)equilibrium expression of the photon current in the direction of the vorticity. We briefly discuss the relevance of this “photonic chiral vortical effect” in pulsars and rotating massive stars and its possible realization in semiconductors.

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N. Yamamoto
Wed, 1 Mar 17
7/67

Comments: 9 pages

The gluon condensation at high energy hadron collisions [CL]

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http://arxiv.org/abs/1702.02249


We report that the saturation/CGC model of gluon distribution is unstable under action of the chaotic solution in a nonlinear QCD evolution equation, and it evolves to the distribution with a sharp peak at the critical momentum. We find that this gluon condensation is caused by a new kind of shadowing-antishadowing effects, and it leads to a series of unexpected effects in high energy hadron collisions including astrophysical events. For example, the extremely intense fluctuations in the transverse-momentum and rapidity distributions of the gluon jets present the gluon-jet bursts; a sudden increase of the proton-proton cross sections may fill the GZK suppression; the blocking QCD evolution will restrict the maximum available energy of the hadron-hadron colliders.

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W. Zhu and J. Lan
Thu, 9 Feb 17
58/67

Comments: 45 pages, 19 figures, to be published in Nucl. Phys. B

Neutron Stars in the Laboratory [HEAP]

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http://arxiv.org/abs/1610.06882


Neutron stars are astrophysical laboratories of many extremes of physics. Their rich phenomenology provides insights into the state and composition of matter at densities which cannot be reached in terrestrial experiments. Since the core of a mature neutron star is expected to be dominated by superfluid and superconducting components, observations also probe the dynamics of large-scale quantum condensates. The testing and understanding of the relevant theory tends to focus on the interface between the astrophysics phenomenology and nuclear physics. The connections with low-temperature experiments tend to be ignored. However, there has been dramatic progress in understanding laboratory condensates (from the different phases of superfluid helium to the entire range of superconductors and cold atom condensates). In this review, we provide an overview of these developments, compare and contrast the mathematical descriptions of laboratory condensates and neutron stars and summarise the current experimental state-of-the-art. This discussion suggests novel ways that we may make progress in understanding neutron star physics using low-temperature laboratory experiments.

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V. Graber, N. Andersson and M. Hogg
Mon, 24 Oct 16
6/53

Comments: N/A

Detecting continuous gravitational waves with superfluid $^4$He [CL]

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http://arxiv.org/abs/1606.04980


Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very high $Q$-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1-1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For reasonable experimental parameters, we find that strain fields on the order of $h\sim 10^{-23} /\sqrt{\rm Hz}$ are detectable. We show that the proposed system can significantly improve the limits on gravitational wave strain from nearby pulsars within a few months of integration time.

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S. Singh, L. Lorenzo, I. Pikovski, et. al.
Fri, 17 Jun 16
65/65

Comments: N/A

On the Detectability of Light Dark Matter with Superfluid Helium [CL]

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http://arxiv.org/abs/1604.08206


We show that a two-excitation process in superfluid helium, combined with sensitivity to meV energy depositions, can probe dark matter down to the ~keV warm dark matter mass limit. This mass reach is three orders of magnitude below what can be probed with ordinary nuclear recoils in helium at the same energy resolution. The kinematics of the process requires the two athermal excitations to have nearly equal and opposite momentum, potentially providing a built-in coincidence mechanism for controlling backgrounds.

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K. Schutz and K. Zurek
Fri, 29 Apr 16
11/57

Comments: 5 pages, 2 figures

Half-quantized Non-Abelian Vortices in Neutron $^3P_2$ Superfluids inside Magnetars [CL]

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http://arxiv.org/abs/1602.07050


We point out that half-quantized non-Abelian vortices exist as the minimum energy states in rotating neutron $^3P_2$ superfluids in the inner cores of magnetars with magnetic field greater than $3 \times 10^{15}$ Gauss, while they do not in ordinary neutron stars with smaller magnetic fields. One integer vortex is split into two half-quantized vortices. The number of vortices is about $10^{19}$ and they are separated at about $\mu$m in a vortex lattice for typical parameters, while the vortex core size is about 10-100 fm. They are non-Abelian vortices characterized by non-Abelian first homotopy group, and consequently when two vortices corresponding to non-commutative elements collide, a rung vortex must be created between them, implying the formation of an entangled vortex network inside the cores of magnetars. We find the spontaneous magnetization in the vortex core showing anti-ferromagnetism whose typical magnitude is about $10^{8-9}$ Gauss that is ten times larger than that of integer vortices, when external magnetic fields are present along the vortex line.

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K. Masuda and M. Nitta
Wed, 24 Feb 16
23/48

Comments: 7 pages, 2 figures

CO2 hydrate dissociation at low temperatures – formation and annealing of ice Ic [CL]

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http://arxiv.org/abs/1510.08004


Dissociation of gas hydrates below 240 K leads to the formation of a metastable form of water ice, so called cubic ice (Ic). Through its defective nature and small particle size the surface film composed of such material is incapable of creating any significant diffusion barrier. Above 160 K, cubic ice gradually transforms to the stable hexagonal (Ih) form on laboratory time scales. The annealing, coupled with a parallel decomposition of gas hydrates, accelerates as temperature rises but already above 190 K the first process prevails, transforming cubic stacking sequences in-to ordinary Ih ice within a few minutes. Remaining stacking faults are removed through very slow isothermal annealing or after heating up above 240 K. The role of the proportion of cubic stacking on the decomposition rate is discussed. A better understanding of the dissociation kinetics at low temperatures is particularly im-portant for the critical evaluation of existing hypotheses that consider clathrates as a potential medium that actively participate in geological processes or is able to store gases (e.g. CH4, CO2 or Xe) in environments like comets, icy moons (i. e. Titan, Europa, Enceladus) or on Mars. Here, we present kinetics studies on the dissociation of CO2 clathrates at isothermal and isobaric conditions between 170 and 190K and mean Martian surface pressure. We place special attention to the formed ice and demonstrate its influence on the dissociation rates with a combination of neutron diffraction studies (performed on D20 at ILL/Grenoble) and cryo-SEM. More detailed crystallo-graphic information has been acquired via a flexible stacking-fault model capable of revealing the time evolution of the defect structure of ice Ic in terms of stacking probabilities and crystal size.

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A. Falenty, T. Hansen and W. Kuhs
Wed, 28 Oct 15
57/79

Comments: Unpublished contribution to the 7th International Conference on Gas Hydrates (ICGH-7), Edinburgh, UK, 17-21 July 2011 (was only available to the conference participants)

A Dark Matter Superfluid [CEA]

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http://arxiv.org/abs/1507.03013


In this talk we present a novel framework that unifies the stunning success of MOND on galactic scales with the triumph of the LambdaCDM model on cosmological scales. This is achieved through the rich and well-studied physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter particles and mediate a MOND-like force. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures, which we briefly discuss. Remarkably the critical temperature and equation of state of the dark matter superfluid are similar to those of known cold atom systems. Identifying a precise cold atom analogue would give important insights on the microphysical interactions underlying DM superfluidity. Tantalizingly, it might open the possibility of simulating the properties and dynamics of galaxies in laboratory experiments.

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J. Khoury
Tue, 14 Jul 15
39/64

Comments: 8 pages. To appear in the proceedings of the 2015 Rencontres de Moriond, “Gravitation: 100 years after GR”

Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure [CL]

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http://arxiv.org/abs/1506.01403


We extend the solid-state nudged elastic band method to handle a non-conserved order parameter – in particular, magnetization, that couples to volume and leads to many observed effects in magnetic systems. We apply this formalism to the well-studied magneto-volume collapse during the pressure-induced transformation in iron – from ferromagnetic body-centered cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We find a bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and coherent stress occurs at the transition state, which has a form of a cusp on the potential-energy surface (yet all the atomic and cell degrees of freedom are continuous); the calculated pressure jump of 25 GPa is related to the observed 25 GPa spread in measured coexistence pressures arising from martensitic and coherency stresses in samples. Our results agree with experiments, but necessarily differ from those arising from drag and restricted parametrization methods having improperly constrained or uncontrolled degrees of freedom.

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N. Zarkevich and D. Johnson
Fri, 5 Jun 15
26/63

Comments: 7 pages, 7 figures

Oscillatory superfluid Ekman pumping in Helium II and neutron stars [CL]

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http://arxiv.org/abs/1505.00293


The linear response of a superfluid, rotating uniformly in a cylindrical container and threaded with a large number of vortex lines, to an impulsive increase in the angular velocity of the container is investigated. At zero temperature and with perfect pinning of vortices to the top and bottom of the container, we demonstrate that the system oscillates persistently with a frequency proportional to the vortex line tension parameter to the quarter power. This low-frequency mode is generated by a secondary flow analogous to classical Ekman pumping that is periodically reversed by the vortex tension in the boundary layers. We compare analytic solutions to the two-fluid equations of Chandler & Baym (1986) with the spin-up experiments of Tsakadze & Tsakadze (1980) in helium II and find the frequency agrees within a factor of four, although the experiment is not perfectly suited to the application of the linear theory. We argue that this oscillatory Ekman pumping mode, and not Tkachenko modes provide a natural explanation for the observed oscillation. In neutron stars, the oscillation period depends on the pinning interaction between neutron vortices and flux tubes in the outer core. Using a simplified pinning model, we demonstrate that strong pinning can accommodate modes with periods of days, which are only weakly damped by mutual friction over a timescale of months.

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C. Eysden
Tue, 5 May 15
7/51

Comments: 25 pages, 6 figures, submitted to Journal of Fluid Mechanics

Thermal conductivity of the neutron star crust: A reappraisal [HEAP]

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http://arxiv.org/abs/1503.01696


We use classical and quantum Monte Carlo techniques to study the static structure function $S(q)$ of a one-component ion lattice and use it to calculate the thermal conductivity $\kappa$ of high-density solid matter expected in the neutron star crust. We also calculate the phonon spectrum using the dynamic-matrix method and use it to obtain $\kappa$ in the one-phonon approximation. We compare the results obtained with these methods and assess the validity of some commonly used approximations in the literature. We find that quantum effects became relevant for the calculation of $\kappa$ when the temperature $T\lesssim 0.3~\Omega_\mathrm{P}$, where $\Omega_\mathrm{P}$ is the ion plasma frequency. Dynamical information beyond the static structure becomes relevant when $T\lesssim 0.1~\Omega_\mathrm{P}$. We discuss the implications of these findings for calculations of $\kappa$ in multi-component systems and identify strategies for using Monte Carlo techniques in future work.

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S. Abbar, J. Carlson, H. Duan, et. al.
Fri, 6 Mar 15
17/51

Comments: 8 pages, 4 figures

Cubic wavefunction deformation of compressed atoms [CL]

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http://arxiv.org/abs/1502.03781


We hypothesize that in a non-metallic crystalline structure under extreme pressures, atomic wavefunctions deform to adopt a reduced rotational symmetry consistent with minimizing interstitial space in the crystal. We exemplify with a simple numeric variational calculation that yields the energy cost of this deformation for Helium to 25%. Balancing this with the free energy gained by tighter packing we obtain the pressures required to effect such deformation. The consequent modification of the structure suggests a decrease in the resistance to tangential stress, and an associated decrease of the crystal’s shear modulus. The atomic form factor is also modified. We also compare with neutron matter in the interior of compact stars.

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P. Portela and F. Llanes-Estrada
Fri, 13 Feb 15
27/63

Comments: 6 pages, 13 figure files

The Leading Correction to the Thomas-Fermi Model at Finite Temperature [CL]

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http://arxiv.org/abs/1412.2402


The semi-classical approach leading to the Thomas-Fermi (TF) model provides a simple universal thermodynamic description of the electronic cloud surrounding the nucleus in an atom. This model is known to be exact at the limit of $Z\rightarrow\infty$, i.e., infinite nuclear charge, at finite density and temperature. Motivated by the zero-temperature case, we show in the current letter that the correction to TF due to quantum treatment of the strongly bound inner-most electrons, for which the semi-classical approximation breaks, scales as $Z^{-1/3}$, with respect to the TF solution. As such, it is more dominant than the quantum corrections to the kinetic energy, as well as exchange and correlation, which are known to be suppressed by $Z^{-2/3}$. We conjecture that this is the leading correction for this model. In addition, we present a different free energy functional for the TF model, and a successive functional that includes the strongly bound electrons correction. We use this corrected functional to derive a self-consistent potential and the electron density in the atom, and to calculate the corrected energy. At this stage, our model has a built-in validity limit, breaking as the L shell ionizes.

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E. Segev and D. Gazit
Tue, 9 Dec 14
55/64

Comments: 5 pages, 4 figures, 1 table

Iron under pressure: bcc-hcp equilibrium coexistence revisited [CL]

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http://arxiv.org/abs/1412.1849


We revisit results from decades of pressure experiments on the bcc – hcp transformations in iron, which are sensitive to non-hydrostatic conditions and sample size. We emphasize the role of martensitic stress in the observed pressure hysteresis and address the large spread in values for onset pressures of the nucleating phase. From electronic-structure calculations, we find a bcc – hcp equilibrium coexistence pressure of 8.4 GPa. Accounting for non-hydrostatic martensitic stress and a stress-dependent transition barrier, we suggest a pressure inequality for better comparison to experiment and observed hysteresis. We construct the equation of state for bcc and hcp phases under hydrostatic pressure, and compare to experiments and previous calculations.

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N. Zarkevich and D. Johnson
Mon, 8 Dec 14
20/61

Comments: 9 pages, 1 figure, 199 citations

Bose-Einstein Condensate strings [CL]

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http://arxiv.org/abs/1410.6899


We consider the possible existence of gravitationally bound general relativistic strings consisting of Bose-Einstein Condensate (BEC) matter which is described, in the Newtonian limit, by the zero temperature time-dependent nonlinear Schr{\”}odinger equation (the Gross-Pitaevskii equation), with repulsive inter-particle interactions. In the Madelung representation of the wave function, the quantum dynamics of the condensate can be formulated in terms of the classical continuity equation and the hydrodynamic Euler equations. In the case of a condensate with quartic nonlinearity, the condensates can be described as a gas with two pressure terms, the interaction pressure, which is proportional to the square of the matter density, and the quantum pressure, which is without any classical analogue though, when the number of particles in the system is high enough, the latter may be neglected. By assuming cylindrical symmetry, we analyze the physical properties of the BEC strings in both the interaction pressure and quantum pressure dominated limits, by numerically integrating the gravitational field equations. In this way we obtain a large class of stable string-like astrophysical objects, whose basic parameters (mass density and radius) depend sensitively on the mass and scattering length of the condensate particle, as well as on the quantum pressure of the Bose-Einstein gas.

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T. Harko and M. Lake
Tue, 28 Oct 14
56/67

Comments: 18 pages, 16 figures. arXiv admin note: text overlap with arXiv:hep-ph/0504083 by other authors

Astrophysical Bose-Einstein Condensates and Superradiance [CL]

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http://arxiv.org/abs/1408.0790


We investigate gravitational analogue models to describe slowly rotating objects (e.g., dark-matter halos, or boson stars) in terms of Bose-Einstein condensates, trapped in their own gravitational potentials. We begin with a modified Gross-Pitaevskii equation, and show that the resulting background equations of motion are stable, as long as the rotational component is treated as a small perturbation. The dynamics of the fluctuations of the velocity potential are effectively governed by the Klein-Gordon equation of a “Eulerian metric”, where we derive the latter by the use of a relativistic Lagrangian extrapolation. Superradiant scattering on such objects is studied. We derive conditions for its occurence and estimate its strength. Our investigations might give an observational handle to phenomenologically constrain Bose-Einstein condensates.

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F. Kuhnel and C. Rampf
Tue, 5 Aug 14
52/61

Comments: 20 pages, 3 figures

Giant Planets [EPA]

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http://arxiv.org/abs/1405.3752


We review the interior structure and evolution of Jupiter, Saturn, Uranus and Neptune, and giant exoplanets with particular emphasis on constraining their global composition. Compared to the first edition of this review, we provide a new discussion of the atmospheric compositions of the solar system giant planets, we discuss the discovery of oscillations of Jupiter and Saturn, the significant improvements in our understanding of the behavior of material at high pressures and the consequences for interior and evolution models. We place the giant planets in our Solar System in context with the trends seen for exoplanets.

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T. Guillot and D. Gautier
Fri, 16 May 14
32/55

Comments: This chapter has been finished in February 2014 for publication in the second edition of the Treatise on Geophysics. 42 pages, 16 figures

Rotating analogue black holes: Quasinormal modes and tails, superresonance, and sonic bombs and plants in the draining bathtub acoustic hole [CL]

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http://arxiv.org/abs/1312.7176


The analogy between sound wave propagation and light waves led to the study of acoustic holes, the acoustic analogues of black holes. Many black hole features have their counterparts in acoustic holes. The Kerr metric, the rotating metric for black holes in general relativity, has as analogue the draining bathtub metric, a metric for a rotating acoustic hole. Here we report on the progress that has been made in the understanding of features, such as quasinormal modes and tails, superresonance, and instabilities when the hole is surrounded by a reflected mirror, in the draining bathtub metric. Given then the right settings one can build up from these instabilities an apparatus that stores energy in the form of amplified sound waves. This can be put to wicked purposes as in a bomb, or to good profit as in a sonic plant.

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Tue, 31 Dec 13
20/49