Absolute stability window and upper bound on the magnetic field strength in a strongly magnetized strange quark star [CL]


Magnetized strange quark stars, composed of strange quark matter (SQM) and self-bound by strong interactions, can be formed if the energy per baryon of magnetized SQM is less than that of the most stable $^{56}$Fe nucleus under the zero external pressure and temperature. Utilizing the MIT bag model description of magnetized SQM under charge neutrality and beta equilibrium conditions, the corresponding absolute stability window in the parameter space of the theory is determined. It is shown that there exists the maximum magnetic field strength allowed by the condition of absolute stability of magnetized SQM. The value of this field, $H\sim3\cdot10^{18}$ G, represents the upper bound on the magnetic field strength which can be reached in a strongly magnetized strange quark star.

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A. Isayev
Wed, 17 Jan 18

Comments: 9 pages, 2 figures. arXiv admin note: text overlap with arXiv:1501.07772

The IRON Project: Photoionization of Fe ions [CL]


The IRON Project, initiated in 1991, aims at two main objectives, i) study the characteristics of and calculate large-scale high accuracy data for atomic radiative and collisional processes, and ii) application in solving astrophysical problems. It focuses on the complex iron and iron-peak elements commonly observed in the spectra of astrophysical plasmas. The present report will illustrate the characteristics of the dominant atomic process of photoionization that have been established under the project and the preceding the Opacity Project and their importance in applications.

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S. Nahar
Wed, 17 Jan 18

Comments: 12 pages, 9 figures, Workshop on Astrophysical Opacities, Western Michigan University, Kalamazoo, Michigan, USA August 1 – 4, 2017

Random projections in gravitational wave searches of compact binaries [CL]


Random projection (RP) is a powerful dimension reduction technique widely used in analysis of high dimensional data. We demonstrate how this technique can be used to improve the computational efficiency of gravitational wave searches from compact binaries of neutron stars or black holes. Improvements in low-frequency response and bandwidth due to detector hardware upgrades pose a data analysis challenge in the advanced LIGO era as they result in increased redundancy in template databases and longer templates due to higher number of signal cycles in band. The RP-based methods presented here address both these issues within the same broad framework. We first use RP for an efficient, singular value decomposition inspired template matrix factorization and develop a geometric intuition for why this approach works. We then use RP to calculate approximate time-domain correlations in a lower dimensional vector space. For searches over parameters corresponding to non-spinning binaries with a neutron star and a black hole, a combination of the two methods can reduce the total on-line computational cost by an order of magnitude over a nominal baseline. This can, in turn, help free-up computational resources needed to go beyond current spin-aligned searches to more complex ones involving generically spinning waveforms.

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S. Kulkarni, K. Phukon, A. Reza, et. al.
Tue, 16 Jan 18

Comments: N/A

Nuclear mass predictions based on Bayesian neural network approach with pairing and shell effects [CL]


Bayesian neural network (BNN) approach is employed to improve the nuclear mass predictions of various models. It is found that the noise error in the likelihood function plays an important role in the predictive performance of the BNN approach. By including a distribution for the noise error, an appropriate value can be found automatically in the sampling process, which optimizes the nuclear mass predictions. Furthermore, two quantities related to nuclear pairing and shell effects are added to the input layer in addition to the proton and mass numbers. As a result, the theoretical accuracies are significantly improved not only for nuclear masses but also for single-nucleon separation energies. Due to the inclusion of the shell effect, in the unknown region, the BNN approach predicts a similar shell-correction structure to that in the known region, e.g., the predictions of underestimation of nuclear mass around the magic numbers in the relativistic mean-field model. This manifests that better predictive performance can be achieved if more physical features are included in the BNN approach.

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Z. Niu and H. Liang
Tue, 16 Jan 18

Comments: 15 pages, 4 figures, and 3 tables

Imprints of the nuclear symmetry energy on the tidal deformability of neutron stars [CL]


Applying an equation of state (EOS) with its symmetric nuclear matter (SNM) part and the low-density symmetry energy $E_{sym}(\rho)$ constrained by heavy-ion reaction data, we calculate the tidal deformability $\lambda$ of neutron stars in coalescing binary systems. Corresponding to the partially constrained EOS that predicted earlier a radius of 11.5 km $< R_{1.4} <$ 13.6 km for canonical neutron star configurations, $\lambda$ is found to be in the range of $\sim[1.7 – 3.9]\times 10^{36}$ (gr cm$^2$s$^2$) consistent with the very recent observation of the GW170817/AT2017gfo event. The upper limit for the radius of canonical neutron stars inferred from the GW170817 event is consistent with but less restrictive than the earlier prediction based on the EOS partially constrained by the terrestrial nuclear laboratory experiments. Coherent analyses of dense neutron-rich nuclear matter EOS underlying both nuclear laboratory experiments and astrophysical observations are emphasized.

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P. Krastev and B. Li
Tue, 16 Jan 18

Comments: 8 pages, 5 figures, 1 table

A radiative neutrino mass model in light of DAMPE excess with hidden gauged $U(1)$ symmetry [CL]


We propose a one-loop induced neutrino mass model with hidden $U(1)$ gauge symmetry, in which we successfully involve a bosonic dark matter (DM) candidate propagating inside a loop diagram in neutrino mass generation to explain electron/positron excess recently reported by DArk Matter Particle Explorer (DAMPE). In our scenario dark matter annihilates into four leptons through $Z’$ boson as DM DM $\to Z’ Z’ (Z’ \to \ell^+ \ell^-)$ and $Z’$ decays into leptons via one-loop effect. We then investigate branching ratios of $Z’$ taking into account lepton flavor violations and neutrino oscillation data.

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T. Nomura, H. Okada and P. Wu
Tue, 16 Jan 18

Comments: 14 pages, 5 figures, 1 table

Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds [CL]


Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as $m_g < 1.2 \times 10^{-22}$ eV Abbott et al. (2016).
In the paper we analyze a potential to reduce upper bounds for graviton mass with future observational data on trajectories of bright stars near the Galactic Center.Since gravitational potentials are different for these two cases, expressions for relativistic advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity (Borka et al., 2013) and graviton mass (Zakharov et al. 2016) from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around $5 \times 10^{-23}$ eV or slightly better than current estimates obtained with LIGO observations.

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A. Zakharov, P. Jovanovic, D. Borka, et. al.
Tue, 16 Jan 18

Comments: 15 pages, 1 Figure, 1 Table