5,927 research outputs found
Effects of curvature and interactions on the dynamics of the deconfinement phase transition
We study the dynamics of first-order cofinement-deconfinement phase
transition through nucleation of hadronic bubbles in an expanding quark gluon
plasma in the context of heavy ion collisions for interacting quark and hadron
gas and by incorporating the effects of curvature energy. We find that the
interactions reduce the delay in the phase transition whereas the curvature
energy has a mixed behavior. In contrast to the case of early Universe phase
transition, here lower values of surface tension increase the supercooling and
slow down the hadronization process. Higher values of bag pressure tend to
speed up the transition. Another interesting feature is the start of the
hadronization process as soon as the QGP is created.Comment: LaTeX, 17 pages including 14 postscript figure
Yarkovsky Drift Detections for 247 Near-Earth Asteroids
The Yarkovsky effect is a thermal process acting upon the orbits of small
celestial bodies, which can cause these orbits to slowly expand or contract
with time. The effect is subtle (da/dt ~ 10^-4 au/My for a 1 km diameter
object) and is thus generally difficult to measure. We analyzed both optical
and radar astrometry for 600 near-Earth asteroids (NEAs) for the purpose of
detecting and quantifying the Yarkovsky effect. We present 247 NEAs with
measured drift rates, which is the largest published set of Yarkovsky
detections. This large sample size provides an opportunity to examine the
Yarkovsky effect in a statistical manner. In particular, we describe two
independent population-based tests that verify the measurement of Yarkovsky
orbital drift. First, we provide observational confirmation for the Yarkovsky
effect's theoretical size dependence of 1/D, where D is diameter. Second, we
find that the observed ratio of negative to positive drift rates in our sample
is 2.34, which, accounting for bias and sampling uncertainty, implies an actual
ratio of . This ratio has a vanishingly small probability of
occurring due to chance or statistical noise. The observed ratio of retrograde
to prograde rotators is two times lower than the ratio expected from numerical
predictions from NEA population studies and traditional assumptions about the
sense of rotation of NEAs originating from various main belt escape routes. We
also examine the efficiency with which solar energy is converted into orbital
energy and find a median efficiency in our sample of 12%. We interpret this
efficiency in terms of NEA spin and thermal properties.Comment: 27 pages, 9 figures, published in the Astronomical Journal, 159, 92,
202
Near-IR studies of recurrent nova V745 Scorpii during its 2014 outburst
The recurrent nova (RN) V745 Scorpii underwent its third known outburst on
2014 February 6. Infrared monitoring of the eruption on an almost daily basis,
starting from 1.3d after discovery, shows the emergence of a powerful blast
wave generated by the high velocity nova ejecta exceeding 4000 kms
plowing into its surrounding environment. The temperature of the shocked gas is
raised to a high value exceeding 10K immediately after outburst
commencement. The energetics of the outburst clearly surpass those of similar
symbiotic systems like RS Oph and V407 Cyg which have giant secondaries. The
shock does not show a free-expansion stage but rather shows a decelerative
Sedov-Taylor phase from the beginning. Such strong shockfronts are known to be
sites for ray generation. V745 Sco is the latest nova, apart from five
other known novae, to show ray emission. It may be an important
testbed to resolve the crucial question whether all novae are generically
ray emitters by virtue of having a circumbinary reservoir of material
that is shocked by the ejecta rather than ray generation being
restricted to only symbiotic systems with a shocked red giant (RG) wind. The
lack of a free-expansion stage favors V745 Sco to have a density enhancement
around the white dwarf (WD), above that contributed by a RG wind. Our analysis
also suggests that the WD in V745 Sco is very massive and a potential
progenitor for a future SN Ia explosion.Comment: To appear in ApJ (Letters
Anomalous change in leakage and displacement currents after electrical poling on lead-free ferroelectric ceramics
We report the polarization, displacement current and leakage current behavior
of a trivalent nonpolar cation Al cation substituted lead free ferroelectric
NBT-BT electroceramics with tetragonal phase and P4mm space group symmetry.
Nearly three orders of magnitude decrease in leakage current were observed
under electrical poling, which significantly improves microstructure,
polarization, and displacement current. Effective poling neutralizes the domain
pinning, traps charges at grain boundaries and fills oxygen vacancies with free
charge carriers in matrix, thus saturated macroscopic polarization in contrast
to that in upoled samples. E-poling changes bananas type polarization loops to
real ferroelectric loops.Comment: 18 pages, 5 figure
Path Integral Approach to Residual Gauge Fixing
In this paper we study the question of residual gauge fixing in the path
integral approach for a general class of axial-type gauges including the
light-cone gauge. We show that the two cases -- axial-type gauges and the
light-cone gauge -- lead to very different structures for the explicit forms of
the propagator. In the case of the axial-type gauges, fixing the residual
symmetry determines the propagator of the theory completely. On the other hand,
in the light-cone gauge there is still a prescription dependence even after
fixing the residual gauge symmetry, which is related to the existence of an
underlying global symmetry.Comment: revtex 13pages, slightly expanded discussion, version to be published
in Physical Review
THERMAL EFFECTS ON THE CATALYSIS BY A MAGNETIC FIELD
We show that the formation of condensates in the presence of a constant
magnetic field in 2+1 dimensions is extremely unstable. It disappears as soon
as a heat bath is introduced with or without a chemical potential. We point out
some new nonanalytic behavior that develops in this system at finite
temperature.Comment: 10 pages, plain Te
Monodromy Matrix in the PP-Wave Limit
We construct the monodromy matrix for a class of gauged WZWN models in the
plane wave limit and discuss various properties of such systems.Comment: 16 page
Quantization in a General Light-front Frame
In this paper, we study the question of quantization of quantum field
theories in a general light-front frame. We quantize scalar, fermion as well as
gauge field theories in a systematic manner carrying out the Hamiltonian
analysis carefully. The decomposition of the fields into positive and negative
frequency terms needs to be done carefully after which we show that the (anti)
commutation relations for the quantum operators become frame independent. The
frame dependence is completely contained in the functions multiplying these
operators in the field decomposition. We derive the propagators from the vacuum
expectation values of the time ordered products of the fields.Comment: 14 pages, revtex, version to be published in Phys. Rev. D with the
discussion of Abelian field quantization replaced by the non-Abelian field
and some comments added on the Mandelstam-Liebbrandt prescriptio
Light-front Schwinger Model at Finite Temperature
We study the light-front Schwinger model at finite temperature following the
recent proposal in \cite{alves}. We show that the calculations are carried out
efficiently by working with the full propagator for the fermion, which also
avoids subtleties that arise with light-front regularizations. We demonstrate
this with the calculation of the zero temperature anomaly. We show that
temperature dependent corrections to the anomaly vanish, consistent with the
results from the calculations in the conventional quantization. The gauge
self-energy is seen to have the expected non-analytic behavior at finite
temperature, but does not quite coincide with the conventional results.
However, the two structures are exactly the same on-shell. We show that
temperature does not modify the bound state equations and that the fermion
condensate has the same behavior at finite temperature as that obtained in the
conventional quantization.Comment: 10 pages, one figure, version to be published in Phys. Rev.
Hybrid Stars
Recently there have been important developments in the determination of
neutron star masses which put severe constraints on the composition and
equation of state (EOS) of the neutron star matter. Here we study the effect of
quark and nuclear matter mixed phase on mass radius relationship of neutron
stars employing recent models from two classes of EOS's and discuss their
implications.Comment: 3 pages LaTeX including 2 figures, macros included, Talk presented at
the IX International Symposium on Particles, Strings and Cosmology
(PASCOS'03), TIFR, Mumbai, India, January 3-8,2003. To appear in their
proceeding
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