arXiv subjects

Prashanth Jaikumar

Publications and source records attributed to Prashanth Jaikumar.

65 records · Page 4Linked to original sources

arXiv2004

Bremsstrahlung photons from the bare surface of a strange quark star

The photon emissivity from the bremsstrahlung process ee-> eeγoccuring in the electrosphere at the bare surface of a strange quark star is calculated. For surface temperatures T<10^9K, the photon flux exceeds that of e+e- pairs that are produced via the Schwinger mechanism in the presence of a strong electric field that binds electrons to the surface of the quark star. The average energy of photons emitted from the bremsstrahlung process can be 0.5 MeV or more, which is larger than that in e+e- pair annihilation. The observation of this distinctive photon spectrum would constitute an unmistakable signature of a strange quark star and shed light on color superconductivity at stellar densities.

astro-ph↗

arXiv2004

Neutrino emission in neutron matter from magnetic moment interactions

Neutrino emission drives neutron star cooling for the first several hundreds of years after its birth. Given the low energy ($\sim$ keV) nature of this process, one expects very few nonstandard particle physics contributions which could affect this rate. Requiring that any new physics contributions involve light degrees of freedom, one of the likely candidates which can affect the cooling process would be a nonzero magnetic moment for the neutrino. To illustrate, we compute the emission rate for neutrino pair bremsstrahlung in neutron-neutron scattering through photon-neutrino magnetic moment coupling. We also present analogous differential rates for neutrino scattering off nucleons and electrons that determine neutrino opacities in supernovae. Employing current upper bounds from collider experiments on the tau magnetic moment, we find that the neutrino emission rate can exceed the rate through neutral current electroweak interaction by a factor two, signalling the importance of new particle physics input to a standard calculation of relevance to neutron star cooling. However, astrophysical bounds on the neutrino magnetic moment imply smaller effects.

astro-ph↗

arXiv2003

A Hagedorn temperature in post-inflationary dynamics?

We consider the possibility of regarding the maximum temperature $\tm$ of a plasma of inflaton decay products as a Hagedorn temperature connected with the transition from an inflaton-dominated epoch to a radiation-dominated universe. Employing a ``bottom-up'' approach to inflaton decay, we show that the limiting temperature $T_{\rm H}\sim m_ϕ$, as obtained from a numerical analysis of the evolution equations, can also be understood theoretically in a Hagedorn picture of the phase transition.

hep-ph↗

arXiv2003

Post-inflationary thermalization with hadronization scenario

We study thermalization of the early Universe when the inflaton can decay into the Standard Model (SM) quarks and gluons, using QCD arguments. We describe the possible formation of the thermal plasma of soft gluons and quarks well before the completion of reheating. Relevant interaction rates of leading order processes and the corresponding thermalization time scale is presented. We discuss hadronization while thermalizing the decay products of the inflaton, when the reheat temperature of the Universe is below the QCD phase transition but above the temperature of the Big Bang nucleosynthesis.

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arXiv2003

Ultra-high energy cosmic rays, cosmological constant, and $θ$-vacua

We propose that the origin of ultra-high energy cosmic rays beyond the GZK cutoff and the origin of small cosmological constant can both be explained by vacuum tunneling effects in a theory with degenerate vacua and fermionic doublets. By considering the possibility of tunneling from a particular winding number state, accompanied by violation of some global quantum number of fermions, the small value of the vacuum dark energy and the production of high energy cosmic rays are shown to be related. We predict that the energy of such cosmic rays should be at least $5\times 10^{14}$ GeV.

hep-ph↗

arXiv2002

Scalar-isoscalar excitation in dense quark matter

We study the spectrum of scalar-isoscalar excitations in the color-flavor locked phase of dense quark matter. The sigma meson in this phase appears as a four-quark state (of diquark and anti-diquark) with a well-defined mass and extremely small width, as a consequence of it's small coupling to two pions. The quark particle/hole degrees of freedom also contribute significantly to the correlator just above the threshold 2Δwhere Δis the superconducting gap.

hep-ph↗

arXiv2002

Neutrino Emission from Goldstone Modes in Dense Quark Matter

We calculate neutrino emissivities from the decay and scattering of Goldstone bosons in the color-flavor-locked (CFL) phase of quarks at high baryon density. Interactions in the CFL phase are described by an effective low-energy theory. For temperatures in the tens of keV range, relevant to the long-term cooling of neutron stars, the emissivities involving Goldstone bosons dominate over those involving quarks, because gaps in the CFL phase are $\sim 100$ MeV while the masses of Goldstone modes are on the order of 10 MeV. For the same reason, the specific heat of the CFL phase is also dominated by the Goldstone modes. Notwithstanding this, both the emissivity and the specific heat from the massive modes remain rather small, because of their extremely small number densities. The values of the emissivity and the specific heat imply that the timescale for the cooling of the CFL core in isolation is $\sim 10^{26}$ y, which makes the CFL phase invisible as the exterior layers of normal matter surrounding the core will continue to cool through significantly more rapid processes. If the CFL phase appears during the evolution of a proto-neutron star, neutrino interactions with Goldstone bosons are expected to be significantly more important since temperatures are high enough ($\sim 20-40$ MeV) to admit large number densities of Goldstone modes.

astro-ph↗

arXiv2002

Photon and dilepton emission rates from high density quark matter

We compute the rates of real and virtual photon (dilepton) emission from dense QCD matter in the color-flavor locked (CFL) phase, focusing on results at moderate densities (3-5 times the nuclear saturation density) and temperatures $T\simeq80$ MeV. We pursue two approaches to evaluate the electromagnetic (e.m.) response of the CFL ground state: (i) a direct evaluation of the photon self energy using quark particle/-hole degrees of freedom, and (ii) a Hidden Local Symmetry (HLS) framework based on generalized mesonic excitations where the $ρ$ meson is introduced as a gauge boson of a local SU(3) color-flavor group. The $ρ$ coupling to generalized two-pion states induces a finite width and allows to address the issue of vector meson dominance (VMD) in the CFL phase. We compare the calculated emissivities (dilepton rates) to those arising from standard hadronic approaches including in-medium effects. For rather large superconducting gaps (several tens of MeV at moderate densities), as suggested by both perturbative and nonperturbative estimates, the dilepton rates from CFL quark matter turn out to be very similar to those obtained in hadronic many-body calculations, especially for invariant masses above $M\simeq0.3$ GeV. A similar observation holds for (real) photon production.

hep-ph↗

arXiv2001

Periodic Theta Vacuum Model and the QCD Instanton Vacuum

We formulate a toy model for the $θ$ vacuum that embodies the n-point moments of the even and odd topological charge densities. The partition function is $2π$ periodic only after resumming over all winding modes. We apply the same analysis to the quenched instanton vacuum at finite $θ$ and derive saddle-point results for the vacuum energy density that are manifestly $2π$ periodic whatever $θ$. We briefly discuss the consequences of unquenching the fermions on our results.

hep-ph↗

arXiv2001

Neutrino Pair Emission from Cooper Pair Breaking and Recombination in Superfluid Quark Matter

For the low energy Standard Model neutrino-matter interactions, we calculate neutrino pair ($ν\barν$) emissivites in superfluid quark matter. Just below the critical temperature, Cooper pairs continuously break and recombine, resulting in the emission of $ν\bar ν$ pairs with a rate that greatly exceeds the standard quark modified Urca and bremsstrahlung rates. At the same baryon density in baryonic and quark matter, the ratio of baryon to quark $ν\barν$ emissivites lies in the range 2-5 for the densities of interest in the long-term cooling of solar mass compact stars. We also find that in matter containing hyperons, $ν\barν$ emission can occur with hyperons of all species.

astro-ph↗

arXiv2001

BCS vs Overhauser pairing in dense (2+1)d QCD

We compare the BCS and Overhauser effect as competing mechanisms for the destabilization of the quark Fermi surface at asymptotically large chemical potential, for the special case of 2 space and 1 time dimension. We use the framework of perturbative one-gluon exchange, which dominates the pairing at $μ/g^2\gg 1$. With screening in matter, we show that in the weak coupling limit the Overhauser effect can compete with the BCS effect only for a sufficiently large number of colors. Both the BCS and the Overhauser gaps are of order $g^{4}/μ$ in Landau gauge.

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