2,901 research outputs found
A Simple Statistical Model for Analysis of QGP-droplet (Fireball) Formation
We construct the density of states for quarks and gluons using the `Thomas -
Fermi model' for atoms and the `Bethe model' for nucleons as templates. With
parameters to take care of the plasma (hydrodynamical) features of the QGP with
a thermal potential for the interaction, we find a window in the parametric
space of the model where observable QGP droplets of 5 fm radius can
occur with transition temperature in the range 140 MeV to 250 MeV. By matching
with the expectations of Lattice Gauge estimates of the QGP-hadron transitions,
we can further narrow the window, thereby restricting the allowed values of the
flow-parameters of the model.Comment: LaTex 11 pages, 8 figure
Nonuniversal Effects in the Homogeneous Bose Gas
Effective field theory predicts that the leading nonuniversal effects in the
homogeneous Bose gas arise from the effective range for S-wave scattering and
from an effective three-body contact interaction. We calculate the leading
nonuniversal contributions to the energy density and condensate fraction and
compare the predictions with results from diffusion Monte Carlo calculations by
Giorgini, Boronat, and Casulleras. We give a crude determination of the
strength of the three-body contact interaction for various model potentials.
Accurate determinations could be obtained from diffusion Monte Carlo
calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te
Black hole microstate geometries from string amplitudes
In this talk we review recent calculations of the asymptotic supergravity
fields sourced by bound states of D1 and D5-branes carrying travelling waves.
We compute disk one-point functions for the massless closed string fields. At
large distances from the branes, the effective open string coupling is small,
even in the regime of parameters where the classical D1-D5-P black hole may be
considered. The fields sourced by the branes differ from the black hole
solution by various multipole moments, and have led to the construction of a
new 1/8-BPS ansatz in type IIB supergravity.Comment: 14 pages, 3 figures, Contribution to the proceedings of the Black
Objects in Supergravity School, Frascati, 201
Comments on black holes I: The possibility of complementarity
We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who
argue against black hole complementarity based on the claim that an infalling
observer 'burns' as he approaches the horizon. We show that in fact
measurements made by an infalling observer outside the horizon are
statistically identical for the cases of vacuum at the horizon and radiation
emerging from a stretched horizon. This forces us to follow the dynamics all
the way to the horizon, where we need to know the details of Planck scale
physics. We note that in string theory the fuzzball structure of microstates
does not give any place to 'continue through' this Planck regime. AMPS argue
that interactions near the horizon preclude traditional complementarity. But
the conjecture of 'fuzzball complementarity' works in the opposite way: the
infalling quantum is absorbed by the fuzzball surface, and it is the resulting
dynamics that is conjectured to admit a complementary description.Comment: 34 pages, 6 figures, v3: clarifications & references adde
Heavy Baryons in a Quark Model
A quark model is applied to the spectrum of baryons containing heavy quarks.
The model gives masses for the known heavy baryons that are in agreement with
experiment, but for the doubly-charmed baryon Cascade_{cc}, the model
prediction is too heavy. Mixing between the Cascade_Q and Cascade_Q^\prime
states is examined and is found to be small for the lowest lying states. In
contrast with this, mixing between the Cascade_{bc} and Cascade_{bc}^\prime
states is found to be large, and the implication of this mixing for properties
of these states is briefly discussed. We also examine heavy-quark spin-symmetry
multiplets, and find that many states in the model can be placed in such
multiplets. We compare our predictions with those of a number of other authors.Comment: Version published in International Journal of Modern Physics
Pressure-induced anomalous magnetism and unconventional superconductivity in CeRhIn5 : 115In-NQR Study under Pressure
We report In nuclear-quadrupole-resonance (NQR) measurements of the
pressure()-induced superconductor CeRhIn in the antiferromagnetic (AF)
and superconducting (SC) states. In the AF region, the internal field
at the In site is substantially reduced from kOe at P=0 to 0.39
kOe at GPa, while the N\'eel temperature slightly changes with
increasing . This suggests that either the size in the ordered moment
or the angle between the direction of and
the tetragonal axis is extrapolated to zero at GPa at
which a bulk SC transition is no longer emergent. In the SC state at
GPa, the nuclear spin-lattice relaxation rate has revealed a
dependence without the coherence peak just below , giving evidence
for the unconventional superconductivity. The dimensionality of the magnetic
flutuations in the normal state are also discussed.Comment: 8pages,4figures,submitted to Phys. Rev. B. Rapid
The Negativity of the Overlap-Based Topological Charge Density Correlator in Pure-Glue QCD and the Non-Integrable Nature of its Contact Part
We calculate the lattice two-point function of topological charge density in
pure-glue QCD using the discretization of the operator based on the overlap
Dirac matrix. Utilizing data at three lattice spacings it is shown that the
continuum limit of the correlator complies with the requirement of
non-positivity at non-zero distances. For our choice of the overlap operator
and the Iwasaki gauge action we find that the size of the positive core is ~2a
(with a being the lattice spacing) sufficiently close to the continuum limit.
This result confirms that the overlap-based topological charge density is a
valid local operator over realistic backgrounds contributing to the QCD path
integral, and is important for the consistency of recent results indicating the
existence of a low-dimensional global brane-like topological structure in the
QCD vacuum. We also confirm the divergent short-distance behavior of the
correlator, and the non-integrable nature of the associated contact part.Comment: 13 pages, 5 figure
Exotic superconductivity in the coexistent phase of antiferromagnetism and superconductivity in CeCu2(Si0.98Ge0.02)2: A Cu-NQR study under hydrostatic pressure
We report a pressure () effect on CeCu(SiGe)
where an antiferromagnetic (AFM) order at 0.75 K coexists with
superconductivity below 0.4 K\@. At pressures exceeding
GPa, the AFM order is suppressed, which demonstrates that the sudden emergence
of AFM order due to the Ge doping is ascribed to the intrinsic lattice
expansion. The exotic superconductivity at GPa is found to evolve into
a typical heavy-fermion one with a line-node gap above GPa\@. We
highlight that the anomalous enhancement in nuclear spin-lattice relaxation
rate that follows a = const. behavior well below at =
0 GPa is characterized by the persistence of low-lying magnetic excitations,
which may be inherent to the coexistent state of antiferromagnetism and
superconductivity.Comment: 5 pages with 4 figures embedded in the text. To be published in J.
Phys. Soc. Jp
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