22 research outputs found

### Iso-curvature fluctuations through axion trapping by cosmic string wakes

We consider wake-like density fluctuations produced by cosmic strings at the
quark-hadron transition in the early universe. We show that low momentum axions
which are produced through the radiation from the axionic string at an earlier
stage, may get trapped inside these wakes due to delayed hadronization in these
overdense regions. As the interfaces, bordering the wakes, collapse, the axions
pick-up momentum from the walls and finally leave the wake regions. These
axions thus can produce large scale iso-curvature fluctuations. We have
calculated the detailed profile of these axionic density fluctuations and
discuss its astrophysical consequences.Comment: 23 pages, 4 figures, RevTe

### Azimuthal flow of decay photons in relativistic nuclear collisions

An overwhelming fraction of photons from relativistic heavy ion collisions
has its origin in the decay of $\pi^0$ and $\eta$ mesons. We calculate the
azimuthal asymmetry of the decay photons for several azimuthally asymmetric
pion distributions. We find that the $k_T$ dependence of the elliptic flow
parameter$v_2$ for the decay photons closely follows the elliptic flow
parameter $v_2^{\pi^0}$ evaluated at $p_T \approx k_T+\delta$, where
$\delta\approx$ 0.1 -- 0.2 GeV, for typical pion distributions measured in
nucleus-nucleus collisions at relativistic energies. Similar results are
obtained for photons from the 2-$\gamma$ decay of $\eta$ mesons. Assuming that
the flow of $\pi^0$ is similar to those for $\pi^+$ and $\pi^-$ for which
independent measurements would be generally available, this ansatz can help in
identifying additional sources for photons. Taken along with quark number
scaling suggested by the recombination model, it may help to estimate $v_2$ of
the parton distributions in terms of azimuthal asymmetry of the decay photons
at large $k_T$.Comment: 6 pages, figures added, references added, with more elaborate
discussion

### Effects of Phase Transition induced density fluctuations on pulsar dynamics

We show that density fluctuations during phase transitions in pulsar cores
may have non-trivial effects on pulsar timings, and may also possibly account
for glitches and anti-glitches. These density fluctuations invariably lead to
non-zero off-diagonal components of the moment of inertia, leading to transient
wobbling of star. Thus, accurate measurements of pulsar timing and intensity
modulations (from wobbling) may be used to identify the specific pattern of
density fluctuations, hence the particular phase transition, occurring inside
the pulsar core. Changes in quadrupole moment from rapidly evolving density
fluctuations during the transition, with very short time scales, may provide a
new source for gravitational waves.Comment: 9 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1412.427

### Strings with a confining core in a Quark-Gluon Plasma

We consider the intersection of N different interfaces interpolating between
different $Z_N$ vacua of an SU(N) gauge theory using the Polyakov loop order
parameter. Topological arguments show that at such a string-like junction, the
order parameter should vanish, implying that the core of this string (i.e. the
junction region of all the interfaces) is in the confining phase. Using the
effective potential for the Polyakov loop proposed by Pisarski for QCD, we use
numerical minimization technique and estimate the energy per unit length of the
core of this string to be about 2.7 GeV/fm at a temperature about twice the
critical temperature. For the parameters used, the interface tension is
obtained to be about 7 GeV/fm$^2$. Lattice simulation of pure gauge theories
should be able to investigate properties of these strings. For QCD with quarks,
it has been discussed in the literature that this $Z_N$ symmetry may still be
meaningful, with quark contributions leading to explicit breaking of this $Z_N$
symmetry. With this interpretation, such {\it QGP} strings may play important
role in the evolution of the quark-gluon plasma phase and in the dynamics of
quark-hadron transition.Comment: 18 pages, 6 figures, RevTe

### Glitches due to (quasi) neutron-vortex scattering in the superfluid inner crust of a pulsar

We revisit the mechanism of vortex unpinning caused by the neutron-vortex
scattering \cite{prad1} in the inner crust of a pulsar. The strain energy
released by the crustquake is assumed to be absorbed in some part of the inner
crust and causes pair-breaking quasi-neutron excitations from the existing free
neutron superfluid in the bulk of the inner crust. The scattering of these
quasi-neutrons with the vortex core normal neutrons unpins a large number of
vortices from the thermally affected regions and results in pulsar glitches. We
consider the geometry of a cylindrical shell of the affected pinning region to
study the implications of the vortex unpinning in the context of pulsar
glitches. We find that a pulsar can release about $\sim 10^{11} - 10^{13}$
vortices by this mechanism. These numbers are equivalent to the glitch size of
orders $\sim 10^{-11} - 10^{-9}$ for Vela-like pulsars with the characteristic
age $\tau \simeq 10^4$ years. We also suggest a possibility of a vortex
avalanche triggered by the movement of the unpinned vortices. A rough estimate
of the glitch size caused by an avalanche shows an encouraging result.Comment: 12 pages, 5 figures, Accepted for publication in PR

### Baryon Inhomogeneity Generation in the Quark-Gluon Plasma Phase

We discuss the possibility of generation of baryon inhomogeneities in a
quark-gluon plasma phase due to moving Z(3) interfaces. By modeling the
dependence of effective mass of the quarks on the Polyakov loop order
parameter, we study the reflection of quarks from collapsing Z(3) interfaces
and estimate resulting baryon inhomogeneities in the context of the early
universe. We argue that in the context of certain low energy scale inflationary
models, it is possible that large Z(3) walls arise at the end of the reheating
stage. Collapse of such walls could lead to baryon inhomogeneities which may be
separated by large distances near the QCD scale. Importantly, the generation of
these inhomogeneities is insensitive to the order, or even the existence, of
the quark-hadron phase transition. We also briefly discuss the possibility of
formation of quark nuggets in this model, as well as baryon inhomogeneity
generation in relativistic heavy-ion collisions.Comment: 11 pages, 2 figures, revtex4, more detailed discussion added about
formation and evolution of Z(3)domain walls in the univers