29,511 research outputs found
Gluon Condensates at Finite Baryon Densities and Temperature
We derive here the equation of state for quark matter with a nontrivial
vacuum structure in QCD at finite temperature and baryon density. Using
thermofield dynamics, the parameters of thermal vacuum and the gluon condensate
function are determined through minimisation of the thermodynamic potential,
along with a self-consistent determination of the effective gluon and quark
masses. The scale parameter for the gluon condensates is related to the SVZ
parameter in the context of QCD sum rules at zero temperature. With inclusion
of quarks in the thermal vacuum the critical temperature at which the gluon
condensate vanishes decreases as compared to that containing only gluons. At
zero temperature, we similarly obtain the critical baryon density for the same
to be about 0.36 fm.Comment: revtex, 28 pages, 6 figures (may be sent on request) IP/BBSR/92-8
Vacuum Structure in QCD with Quark and Gluon Condensates
We consider here the vacuum structure in QCD with both quark and gluon
condensates and a variational ansatz for the ground state. The method is
nonperturbative using only equal time algebra for the field operators. We then
find that a constrained energy minimisation of the Hamiltonian leads to a QCD
vacuum with both quark and gluon condensates for .
Pion decay constant and the charge radius of the pion seem to fix the QCD
coupling constant as 1.28. The approach opens up possibilities of
relating the mysterious vacuum structure with common place hadronic properties.Comment: 20 Pages, 2 Figure pages, REVTEX, IP/BBSR/94-1
A Full Study on the Sun-Earth Connection of an Earth-Directed CME Magnetic Flux Rope
We present an investigation of an eruption event of coronal mass ejection
(CME) magnetic flux rope (MFR) from source active region (AR) NOAA 11719 on 11
April 2013 utilizing observations from SDO, STEREO, SOHO, and WIND spacecraft.
The source AR consists of pre-existing sigmoidal structure stacked over a
filament channel which is regarded as MFR system. EUV observations of low
corona suggest a further development of this MFR system by added axial flux
through tether-cutting reconnection of loops at the middle of sigmoid under the
influence of continuous slow flux motions during past two days. Our study
implies that the MFR system in the AR is initiated to upward motion by
kink-instability and further driven by torus-instability. The CME morphology,
captured in simultaneous three-point coronagraph observations, is fitted with
Graduated Cylindrical Shell (GCS) model and discerns an MFR topology with
orientation aligning with magnetic neutral line in the source AR. This MFR
expands self-similarly and is found to have source AR twist signatures in the
associated near Earth magnetic cloud (MC). We further derived kinematics of
this CME propagation by employing a plethora of stereoscopic as well as single
spacecraft reconstruction techniques. While stereoscopic methods perform
relatively poorly compared to other methods, fitting methods worked best in
estimating the arrival time of the CME compared to in-situ measurements.
Supplied with values of constrained solar wind velocity, drag parameter and 3D
kinematics from GCS fit, we construct CME kinematics from the drag based model
consistent with in-situ MC arrival.Comment: Accepted in The Astrophysical Journal, 17 figures, 18 page
Conserved charge fluctuations using the -measure in heavy-ion collisions
We study the net-charge fluctuations, -measure variable, in high energy
heavy-ion collisions in heavy-ion jet interaction generator (HIJING),
ultrarelativistic quantum molecular dynamics (UrQMD) and hadron resonance gas
(HRG) models for various center-of-mass energies (\sqsn). The effect of
kinematic acceptance and resonance decay, in the pseudorapidity acceptance
interval () and lower transverse momentum ()
threshold, on fluctuation measures are discussed. A strong dependence of
with the in HIJING and UrQMD models is observed as opposed to
results obtained from the HRG model. The dissipation of fluctuation signal is
estimated by fitting the -measure as a function of the . An
extrapolated function for higher values at lower \sqsn is
different from the results obtained from models. Particle species dependence of
and the effect of the selection threshold are discussed in
HIJING and HRG models. The comparison of , at midrapidity, of net-charge
fluctuations at various \sqsn obtained from the models with the data from the
ALICE experiment is discussed. The results from the present work as a function
of and \sqsn will provide a baseline for comparison to
experimental measurements.Comment: 9 pages, 8 figures. Published in Physical Review
Disentangling stopped proton and inclusive net-proton fluctuations at RHIC
The recent results on net-proton and net-charge multiplicity fluctuations
from the beam energy scan program at RHIC have drawn much attention to explore
the critical point in the QCD phase diagram. Experimentally measured protons
contain contribution from various processes such as secondaries from higher
mass resonance decay, production process, and protons from the baryon stopping.
Further, these contributions also fluctuate from event to event and can
contaminate the dynamical fluctuations due to the critical point. We present
the contribution of stopped proton and produced proton fluctuations in the
net-proton multiplicity fluctuation in \auau collisions measured by STAR
experiment at RHIC. The produced net-proton multiplicity fluctuations using
cumulants and their ratios are studied as a function collision energies. After
removing the stopped proton contribution from the inclusive proton multiplicity
distribution, a non-monotonic behavior is even more pronounced in the
net-proton fluctuations around \sqsn = 19.6 GeV, both in and
. The present study will be useful to understand the
fluctuations originating due to critical point.Comment: 7 pages, 6 figure
Freeze-out volume of hot dense fireball
A thermodynamically consistent excluded volume model is proposed to account
for the particle multiplicities obtained from lowest SIS energies to the
highest RHIC energies. The chemical freeze-out volumes lying in a slice of one
unit of rapidity for pions and kaons are separately inferred from this analysis
and the results are compared with the corresponding thermal freeze-out volumes
obtained from the Hanbury-Brown Twiss (HBT) pion interferometry. Furthermore,
we extract the variations of freeze-out number densities for pions and nucleons
with the center-of-mass energy in our model and compare them with the HBT data.Comment: 10 pages, 2 figure
Thermodynamics and Lemaitre-Tolman-Bondi void models
It has been argued in the literature that in order to make a matter dominated
Friedmann-Lemaitre-Robertson-Walker universe compatible with the generalized
second law of thermodynamics, one must invoke dark energy, or modified gravity.
In the present article we investigate if in a similar spirit, inhomogeneous
cosmological models can be motivated on thermodynamic grounds. We examine a
particular minimal void Lemaitre-Tolman-Bondi inhomogeneous model which agrees
well with observations. While on the one hand we find that the entropy
associated with the apparent horizon is not well-behaved thermodynamically, on
the other hand the canonical Weyl curvature entropy shows satisfactory
thermodynamic behavior. We suggest that evolution of canonical Weyl curvature
entropy might be a useful way to evaluate the thermodynamic viability of
inhomogeneous cosmologies.Comment: This version: one paragraph added at the end, acknowledgements and
references added, matches published versio
On the chemical freeze-out criteria in a hot and dense fireball
Intensive investigations of freeze-out criteria in a hot and dense fireball
provide important information regarding particle emission from the fireball. A
systematic comparison of these proposals is presented here in the framework of
a thermodynamically consistent excluded volume model which has been found to
describe the properties of hadron gas (HG) quite well. We find that the impact
of excluded volume correction is considerably large and the average energy per
hadron is 0.9 GeV, stays nearly constant at 0.12/fm and
the normalized entropy density in this model. Moreover, these
values are independent of the beam or center-of-mass energy and also of the
target and beam nuclei. In ideal HG model these quantities show substantial
energy dependence. Further we have compared the predictions of various excluded
volume models in the precise determination of these criteria and we find that
the thermodynamically consistent excluded volume models give the best results.
In addition, we find another important criterion that entropy per hadron has a
constant value at 6 in our model. We hope that these findings will throw
considerable light on the expansion dynamics and the bulk thermodynamic
properties of the fireball before chemical freeze-out.Comment: 8 pages, 4 figure
Bianchi type VI1 cosmological model with wet dark fluid in scale invariant theory of gravitation
In this paper, we have investigated Bianchi type VIh, II and III cosmological
model with wet dark fluid in scale invariant theory of gravity, where the
matter field is in the form of perfect fluid and with a time dependent gauge
function (Dirac gauge). A non-singular model for the universe filled with
disorder radiation is constructed and some physical behaviors of the model are
studied for the feasible VIh (h = 1) space-time.Comment: This paper has been withdrawn as the theory is now becomes subcas
Fourth Order Gravity, Scalar-Tensor-Vector Gravity, and Galaxy Rotation Curves
The Lambda-CDM model is the best fit to cosmological data, and to the
observed galactic rotation curves. However, in the absence of a direct
detection of dark matter one should explore theories such as MOND, and perhaps
also modified gravity theories like fourth order gravity and
Scalar-Tensor-Vector Gravity [STVG] as possible explanations for the
non-Keplerian behaviour of galaxy rotation curves. STVG has a modified law for
gravitational acceleration which attempts to fit data by fixing two free
parameters. We show that, remarkably, the biharmonic equation which we get in
the weak field limit of the field equations in a fourth order gravity theory
implies a modification of Newtonian acceleration which is precisely of the same
repulsive Yukawa form as in the STVG theory, and the corrections could in
principle be large enough to try and explain the observed rotation curves. We
also explain how our model provides a first principles understanding of MOND.
We also show that STVG and fourth order gravity predict an acceleration
parameter whose value is of the same order as in MOND.Comment: 13 pages, 3 figures, major revision including change in title and
conclusions, accepted for publication in Phys. Rev.
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