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Register a new userTesting dark decays of baryons in neutron stars
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We demonstrate that the observation of neutron stars with masses greater than one solar mass places severe demands on any exotic neutron decay mode that could explain the discrepancy between beam and bottle measurements of the neutron lifetime. If the neutron can decay to a stable, feebly-interacting dark fermion, the maximum possible mass of a neutron star is 0.7 solar masses, while all well-measured neutron star masses exceed one solar mass. The survival of $2 M_odot$ neutron stars therefore indicates that any explanation beyond the Standard Model for the neutron lifetime puzzle requires dark matter to be part of a multi-particle dark sector with highly constrained interactions.
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We study the probability for nucleation of quark matter droplets in the dense cold cores of old neutron stars induced by the presence of a self-annihilating dark matter component, $chi$. Using a parameterized form of the equation of state for hadronic and quark phases of ordinary matter, we explore the thermodynamic conditions under which droplet formation is facilitated by the energy injection from $chi$ self-annihilations. We obtain the droplet nucleation time as a function of the dark matter candidate mass, $m_chi$. We discuss further observational consequences.
We find that sub-GeV neutrino portal bosons that carry lepton number can condense inside a proto-neutron star (newly born neutron star). These bosons are produced copiously and form a Bose-Einstein condensate for a range of as yet unconstrained coupling strengths to neutrinos. The condensate is a lepton number superfluid with transport properties that differ dramatically from those encountered in ordinary dense baryonic matter. We discuss how this phase could alter the evolution of proto-neutron stars and comment on the implications for neutrino signals and nucleosynthesis.
As we have pointed out in (arXiv:1806.10107 [hep-ph]), the existence of neutron dark matter decay modes n -> chi + anything, where chi is a dark matter fermion, for the solution of the neutron lifetime problem changes priorities and demands to describe the neutron lifetime tau_n = 888.0(2.0)s, measured in beam experiments and defined by the decay modes n -> p + anything, in the Standard Model (SM). The latter requires the axial coupling constant lambda to be equal to lambda = - 1.2690 (arXiv:1806.10107 [hep-ph]). Since such an axial coupling constant is excluded by experimental data reported by the PERKEO II and UCNA Collaborations, the neutron lifetime tau_n = 888.0(2.0)s can be explained only by virtue of interactions beyond the SM, namely, by the Fierz interference term of order b ~ - 10^{-2} dependent on scalar and tensor coupling constants. We give a complete analysis of all correlation coefficients of the neutron beta decays with polarized neutron, taking into account the contributions of scalar and tensor interactions beyond the SM with the Fierz interference term b ~ - 10^{-2}. We show that the obtained results agree well with the contemporary experimental data that does not prevent the neutron with the rate of the decay modes n -> p + anything, measured in beam experiments, to have dark matter decay modes n -> chi + anything.
A promising probe to unmask particle dark matter is to observe its effect on neutron stars, the prospects of which depend critically on whether captured dark matter thermalizes in a timely manner with the stellar core via repeated scattering with the Fermi-degenerate medium. In this work we estimate the timescales for thermalization for multiple scenarios. These include: (a) spin-0 and spin-$frac{1}{2}$ dark matter, (b) scattering on non-relativistic neutron and relativistic electron targets accounting for the respective kinematics, (c) interactions via a range of Lorentz-invariant structures, (d) mediators both heavy and light in comparison to the typical transfer momenta in the problem. We discuss the analytic behavior of the thermalization time as a function of the dark matter and mediator masses, and the stellar temperature. Finally, we identify parametric ranges where both stellar capture is efficient and thermalization occurs within the age of the universe. For dark matter that can annihilate in the core, these regions indicate parametric ranges that can be probed by upcoming infrared telescopes observing cold neutron stars.
The discovery of non-diffuse sources of gravitational waves through compact-object mergers opens new prospects for the study of physics beyond the Standard Model. In this Letter, we consider the implications of the observation of GW190814, involving a coalescence of a black hole with a $sim$2.6 $M_odot$ compact object, which may be too massive to be a neutron star, given our current knowledge of the nuclear matter equation of state. We consider the possibility of a new force between quarks, suggested in other contexts, that modifies the neutron star equation of state, particularly at supranuclear densities. We evaluate how this modification can impact a neutron stars mass and radius to make the observed heavy compact object more probably a neutron star, rather than a black hole, and suggest that further such objects may yet be found. We note the terrestrial and astrophysical measurements that could confirm our picture.
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