Papers by Armen Sedrakian
Physical Review D
In this work, we consider the consequences of phase transition in dense QCD on the properties of ... more In this work, we consider the consequences of phase transition in dense QCD on the properties of compact stars and implications for the observational program in gravitational wave and X-ray astrophysics. The key underlying assumption of our modeling is a strong first-order phase transition past the point where the hadronic branch of compact stars reaches the two-solar mass limit. Our analysis predicts ultracompact stars with very small radii-in the range of 6-9 km-living on compact star sequences that are entirely consistent with the current multimessenger data. We show that sequences featuring two-solar mass hadronic stars consistent with radiopulsar observations are also consistent with the inferences of large radii for massive neutron stars by NICER X-ray observations of neutron stars and the small radii predicted by gravitational waves analysis of the binary neutron star inspiral event GW170817 for our models that feature a strong first-order QCD phase transition.
Particles, 2021
Particles (ISSN 2571-712X), which is a peer-reviewed, open access journal launched in 2018, has n... more Particles (ISSN 2571-712X), which is a peer-reviewed, open access journal launched in 2018, has now reached a significant milestone—the 100th paper has been published [...]
Exploring Fundamental Issues in Nuclear Physics, 2012
Physical Review C, 1997
Predictions are made for the structure of a second 2 ϩ resonance, the soft dipole mode and unnatu... more Predictions are made for the structure of a second 2 ϩ resonance, the soft dipole mode and unnatural parity modes in the 6 He continuum. We use a structure model which describes the system as a three-body ␣ϩNϩN cluster structure, giving the experimentally known properties of 6 He and 6 Li, and use the distortedwave impulse approximation ͑DWIA͒ reaction theory appropriate for dilute matter. The presence of both resonant and nonresonant structures in the halo excitation continuum is shown to be manifest in chargeexchange reactions as well as inelastic scattering with single nucleons. ͓S0556-2813͑97͒50302-5͔
Physical Review C
A set of hadronic equations of state derived from covariant density functional theory and constra... more A set of hadronic equations of state derived from covariant density functional theory and constrained by terrestrial experiments, and astrophysical observations, in particular by the NICER experiment inferences is used to explore the universal relations among the global properties of compact stars containing heavy baryons at high densities. We confirm the validity of universal I-Love-Q relations connecting the moment of inertia (I), the tidal deformability (), and the spin-induced quadrupole moment (Q) for isolated nonrotating stars. We further confirm the validity of the I-C-Q relations connecting the moment of inertia, compactness (C), and quadrupole moment for uniformly and slowly rotating stars, and extend the validity of these relations to maximally rotating sequences. We then investigate the relations between integral parameters of maximally rotating and static compact stars. The universalities are shown to persist for equations of state and compositions containing hyperons and degrees of freedom. When heavy baryons are included, however, the radial profiles of integrands in expressions of global properties exhibit "bumps", which are not present in the case of nucleonic stars in which case the profiles are smooth. We determine the coefficients entering the universal relations in the case of hyperonic and-resonance containing stars.
Proceedings of the YSU A: Physical and Mathematical Sciences, 2016
We discuss the recently developed energy density functional for hypernuclear matter, which is bas... more We discuss the recently developed energy density functional for hypernuclear matter, which is based on simultaneous calculation of heavy single-$\Lambda$ hypernuclei and compact stars containing hypernuclear core. The nucleonic matter is described in terms of a density-dependent parametrization of nucleon-meson couplings, whereas the hyperonmeson couplings are deduced from the octet model. We identify the parameter space of hyperon-meson couplings for which massive stellar configurations with $M \leq 2.1 M_\odot$ exist and at the same time the laboratory $\Lambda$-hypernuclear data can be described.
Monthly Notices of the Royal Astronomical Society, 2021
We study the oscillation modes of differential rotating remnants of binary neutron star inspirals... more We study the oscillation modes of differential rotating remnants of binary neutron star inspirals by modelling them as incompressible Riemann ellipsoids parametrized by the ratio f of their internal circulation to the rotation frequency. The effects of viscosity and gravitational radiation on the modes are studied, and it is shown that these bodies exhibit generic instability towards gravitational radiation akin to the Chandrasekhar–Friedman–Schutz instability for uniformly rotating stars. The odd-parity modes are unstable for all values of f (except for the spherical model) and deformations, whereas the even parity unstable modes appear only in highly eccentric ellipsoids. We quantify the modification of the modes with the varying mass of the model and the magnitude of the viscosity. The modes are weakly dependent on the range of the masses relevant to binary neutron star mergers. Large turbulent viscosity can lead to a suppression of the gravitational-radiation instability, wherea...
The European Physical Journal A, 2020
We study the composition of nuclear matter at sub-saturation densities, non-zero temperatures, an... more We study the composition of nuclear matter at sub-saturation densities, non-zero temperatures, and isospin asymmetry, under the conditions characteristic of binary neutron star mergers, stellar collapse, and low-energy heavy-ion collisions. The composition includes light clusters with mass number $$A\le 4$$ A ≤ 4 , a heavy nucleus ($$^{56}{Fe}$$ 56 Fe ), the $$\varDelta $$ Δ -resonances, the isotriplet of pions, as well as the $$\Lambda $$ Λ hyperon. The nucleonic mean-fields are computed from a zero-range density functional, whereas the pion-nucleon interactions are treated to leading order in chiral perturbation theory. We show that with increasing temperature and/or density the composition of matter shifts from light-cluster to heavy baryon dominated one, the transition taking place nearly independent of the magnitude of the isospin. Our findings highlight the importance of simultaneous treatment of light clusters and heavy baryons in the astrophysical and heavy-ion physics conte...
Physical Review D, 2019
We study the axion cooling of neutron stars within the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) ... more We study the axion cooling of neutron stars within the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) model, which allows for tree level coupling of electrons to the axion and locks the Peccei-Quinn charges of fermions via an angle parameter. This extends our previous study [Phys. Rev. D 93, 065044 (2016)] limited to hadronic models of axions. We explore the two-dimensional space of axion parameters within the DFSZ model by comparing the theoretical cooling models with the surface temperatures of a few stars with measured surface temperatures. It is found that axions masses ma ≥ 0.06 to 0.12 eV can be excluded by x-ray observations of thermal emission of neutron stars (in particular by those of Cas A), the precise limiting value depending on the angle parameter of the DFSZ model. It is also found that axion emission by electron bremsstrahlung in neutron star crusts is negligible except for the special case where neutron Peccei-Quinn charge is small enough, so that the coupling of neutrons to axions can be neglected.
Physics Letters B, 2018
We study the two-flavor color superconductivity of low-temperature quark matter in the vicinity o... more We study the two-flavor color superconductivity of low-temperature quark matter in the vicinity of chiral phase transition in the quark-meson model where the interactions between quarks are generated by pion and sigma exchanges. Starting from the Nambu-Gor'kov propagator in real-time formulation we obtain finite temperature (real axis) Eliashberg-type equations for the quark selfenergies (gap functions) in terms of the in-medium spectral function of mesons. Exact numerical solutions of the coupled nonlinear integral equations for the real and imaginary parts of the gap function are obtained in the zero temperature limit using a model input spectral function. We find that these components of the gap display a complicated structure with the real part being strongly suppressed above 2∆ 0 , where ∆ 0 is its on-shell value. We find ∆ 0 ≃ 40 MeV close to the chiral phase transition.
Particles, 2019
This Special Issue arose from the presentations of the authors at the international conference “T... more This Special Issue arose from the presentations of the authors at the international conference “The Modern Physics of Compact Stars and Relativistic Gravity 2017” https://indico [...]
The Astrophysical Journal, 1995
ABSTRACT
The Astrophysical Journal, 1995
Physical Review a, 2005
We explore the phase diagram of a two-component ultracold atomic Fermi gas interacting with zero-... more We explore the phase diagram of a two-component ultracold atomic Fermi gas interacting with zero-range forces in the limit of weak coupling. We focus on the dependence of the pairing gap and the free energy on the variations in the number densities of the two species while the total density of the system is held fixed. As the density asymmetry is increased, the system exhibits a transition from a homogenous Bardeen-Cooper-Schrieffer ͑BCS͒ phase to phases with spontaneously broken global space symmetries. One such realization is the deformed Fermi surface superfluidity ͑DFS͒ which exploits the possibility of deforming the Fermi surfaces of the species into ellipsoidal form at zero total momentum of Cooper pairs. The critical asymmetries at which the transition from DFS to the unpaired state occurs are larger than those for the BCS phase. In this precritical region the DFS phase lowers the pairing energy of the asymmetric BCS state. We compare quantitatively the DFS phase to another realization of superconducting phases with broken translational symmetry: the singleplane-wave Larkin-Ovchinnikov-Fulde-Ferrell phase, which is characterized by a nonvanishing center-of-mass momentum of the Cooper pairs. The possibility of the detection of the DFS phase in the time-of-flight experiments is discussed and quantified for the case of 6 Li atoms trapped in two different hyperfine states.
Physical Review C, 2012
Neutrino emission rate from baryonic matter in neutron stars via weak neutral vector interaction ... more Neutrino emission rate from baryonic matter in neutron stars via weak neutral vector interaction is computed up to order O(v 6 F), where vF is the Fermi velocity in units of speed of light. The vector current polarization tensors are evaluated with full vertices which include resummed series in the particle-hole channel. The neutrino emissivity is enhanced compared to the O(v 4 F) order up of 10% for values vF ≤ 0.4 characteristic to baryons in compact stars.
Physical Review A, 2012
We describe an equilibrium state of a rotating trapped atomic condensate, which is characterized ... more We describe an equilibrium state of a rotating trapped atomic condensate, which is characterized by a non-zero internal circulation and spontaneous breaking of the rotational O(2) symmetry with all three major semiaxes of the condensate having different values. The macroscopic rotation of the condensate is supported by a mesh of quantized vortices, whose number density is a function of internal circulation. The oscillation modes of this state are computed and the Goldstone mode associated with the loss of the symmetry is identified. The possible avenues for experimental identification this state are discussed.
Journal of Physics: Conference Series, 2011
Journal of Physics: Conference Series, 2011
Astrophysics, 2014
We discuss a time-dependent generalization of the stationary Ginzburg-Landau theory for two-flavo... more We discuss a time-dependent generalization of the stationary Ginzburg-Landau theory for two-flavor color superconducting quark matter and its modification in the presence of rotation. General expressions are obtained for the relaxation timescales of the order parameter and color-magnetic fields and for the dissipative function, which obtains contributions from the relaxation of the order parameter and Ohmic dissipation. We also obtain a stationary equation that governs the penetration of the color-electric field in the color superconductor.
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Papers by Armen Sedrakian