2,048 research outputs found
String Entanglement and D-branes as Pure States
We study the entanglement of closed strings degrees of freedom in order to
investigate the microscopic structure and statistics of objects as D-branes. By
considering the macroscopic pure state (MPS) limit, whenever the entanglement
entropy goes to zero (in such a way that the macroscopic properties of the
state are preserved), we show that boundary states may be recovered in this
limit and, furthermore, the description through closed string (perturbative)
degrees of freedom collapses. We also show how the thermal properties of branes
and closed strings could be described by this model, and it requires that
dissipative effects be taken into account. Extensions of the MPS analysis to
more general systems at finite temperature are finally emphasized.Comment: 14 pages. Minor improvements. Published in Phys. Rev.
Topological Discrete Algebra, Ground State Degeneracy, and Quark Confinement in QCD
Based on the permutation group formalism, we present a discrete symmetry
algebra in QCD. The discrete algebra is hidden symmetry in QCD, which is
manifest only on a space-manifold with non-trivial topology. Quark confinement
in the presence of the dynamical quarks is discussed in terms of the discrete
symmetry algebra. It is shown that the quark deconfinement phase has the ground
state degeneracy depending on the topology of the space, which gives a
gauge-invariant distinction between the confinement and deconfinement phases.
We also point out that new quantum numbers relating to the fractional quantum
Hall effect exist in the deconfinement phase.Comment: 11 pages, 1 figur
Dynamical mapping method in nonrelativistic models of quantum field theory
The solutions of Heisenberg equations and two-particles eigenvalue problems
for nonrelativistic models of current-current fermion interaction and model are obtained in the frameworks of dynamical mapping method. The
equivalence of different types of dynamical mapping is shown. The connection
between renormalization procedure and theory of selfadjoint extensions is
elucidated.Comment: 14 page
Interior gap superfluidity in a two-component Fermi gas of atoms
A new superfluid phase in Fermi matter, termed as "interior gap" (IG) or
"breached pair", has been recently predicted by Liu and Wilczek [Phys.Rev.Lett.
{\bf 90}, 047002 (2003)]. This results from pairing between fermions of two
species having essentially different Fermi surfaces. Using a nonperturbative
variational approach, we analyze the features, such as energy gap, momentum
distributions, and elementary excitations associated with the predicted phase.
We discuss possible realization of this phase in two-component Fermi gases in
an optical trap.Comment: 5 page
BCS BEC crossover and phase structure of relativistic system: a variational approach
We investigate here the BCS BEC crossover in relativistic systems using a
variational construct for the ground state and the minimization of the
thermodynamic potential. This is first studied in a four fermion point
interaction model and with a BCS type ansatz for the ground state with fermion
pairs. It is shown that the antiparticle degrees of freedom play an important
role in the BCS BEC crossover physics, even when the ratio of fermi momentum to
the mass of the fermion is small. We also consider the phase structure for the
case of fermion pairing with imbalanced populations. Within the ansatz,
thermodynamically stable gapless modes for both fermions and anti fermions are
seen for strong coupling in the BEC regime. We further investigate the effect
of fluctuations of the condensate field by treating it as a dynamical field and
generalize the BCS ansatz to include quanta of the condensate field also in a
boson fermion model with quartic self interaction of the condensate field. It
is seen that the critical temperature decreases with inclusion of fluctuations.Comment: 18 pages, 13 figures, one more section added, title modified, version
to appear in Phys Rev
Superconductivity in CVD Diamond Thin Film Well-Above Liquid Helium Temperature
Diamond has always been adored as a jewel. Even more fascinating is its
outstanding physical properties; it is the hardest material known in the world
with the highest thermal conductivity. Meanwhile, when we turn to its
electrical properties, diamond is a rather featureless electrical insulator.
However, with boron doping, it becomes a p-type semiconductor, with boron
acting as a charge acceptor. Therefore the recent news of superconductivity in
heavily boron-doped diamond synthesized by high pressure sintering was received
with considerable surprise. Opening up new possibilities for diamond-based
electrical devices, a systematic investigation of these phenomena clearly needs
to be achieved. Here we show unambiguous evidence of superconductivity in a
diamond thin film deposited by a chemical vapor deposition (CVD) method.
Furthermore the onset of the superconducting transition is found to be 7.4K,
which is higher than the reported value in ref(7) and well above helium liquid
temperature. This finding establishes the superconductivity to be a universal
property of boron-doped diamond, demonstrating that device application is
indeed a feasible challenge.Comment: 6 pages, 3 figure
Action and Hamiltonian for eternal black holes
We present the Hamiltonian, quasilocal energy, and angular momentum for a
spacetime region spatially bounded by two timelike surfaces. The results are
applied to the particular case of a spacetime representing an eternal black
hole. It is shown that in the case when the boundaries are located in two
different wedges of the Kruskal diagram, the Hamiltonian is of the form , where and are the Hamiltonian functions for the right
and left wedges respectively. The application of the obtained results to the
thermofield dynamics description of quantum effects in black holes is briefly
discussed.Comment: 24 pages, Revtex, 5 figures (available upon request
Color superconducting 2SC+s quark matter and gapless modes at finite temperatures
We investigate the phase diagram of color superconducting quark matter with
strange quarks (2SC+s quark matter) in beta equliibrium at zero as well as
finite temperatures within a Nambu-Jona-Lasinio model. The variational method
as used here allows us to investigate simultaneous formation of condensates in
quark--antiquark as well as in diquark channels. Color and electric charge
neutrality conditions are imposed in the calculation of the thermodynamic
potential. Medium dependance of strange quark mass plays a sensitve role in
maintaining charge neutrality conditions. At zero temperature the system goes
from gapless phase to usual BCS phase through an intermediate normal phase as
density is increased. The gapless modes show a smooth behaviour with respect to
temperature vanishing above a critical temperature which is larger than the BCS
transition temperature. We observe a sharp transition from gapless
superconducting phase to the BCS phase as density is increased for the color
neutral matter at zero temperature. As temperature is increased this however
becomes a smooth transition.Comment: 18 pages, 14 figure
Lepton charge and neutrino mixing in pion decay processes
We consider neutrino mixing and oscillations in quantum field theory and
compute the neutrino lepton charge in decay processes where neutrinos are
generated. We also discuss the proper definition of flavor charge and states
and clarify the issues of the possibility of different mass parameters in field
mixing.Comment: 13 page
Particle-number conservation in static-path approximation for thermal superfluid systems
By applying particle-number projection to the static-path approximation
(SPA), the heat capacity and the breakdown of pairing correlations are
investigated in the thermally excited, superfluid systems 172Yb, 94Mo, and
56Fe. For the heavy nucleus 172Yb, the heat capacities in both the SPA and the
number-projected SPA (NPSPA) exhibit an S shape; the difference between the SPA
and NPSPA heat-capacity curves is not very large and the particle-number
projection thereby enhances the S shape already seen in the SPA. The
temperature at which the S-shape of heat capacity curve occurs parallels the
temperature of the breakdown of pairing correlations as indicated by the
effective pairing gap. However, for the comparatively lighter nuclei 94Mo and
56Fe, the SPA does not produce an S-shaped heat capacity on its own; only after
particle-number projection the S shape appears in the heat-capacity curve. For
94Mo, we compare the NPSPA result with thermal odd-even mass differences, which
are regarded as a direct measure of the pairing gap.Comment: 7 pages, 5 figures, accepted for publication in Phys. Rev.
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