470 research outputs found
Optimal eigenvalues estimate for the Dirac operator on domains with boundary
We give a lower bound for the eigenvalues of the Dirac operator on a compact
domain of a Riemannian spin manifold under the \MIT bag boundary condition.
The limiting case is characterized by the existence of an imaginary Killing
spinor.Comment: 10 page
Gravitational wave background from neutron star phase transition for a new class of equation of state
We study the generation of a stochastic gravitational wave (GW) background
produced by a population of neutron stars (NSs) which go over a hadron-quark
phase transition in its inner shells. We obtain, for example, that the NS phase
transition, in cold dark matter scenarios, could generate a stochastic GW
background with a maximum amplitude of , in the
frequency band for stars forming at redshifts of up
to We study the possibility of detection of this isotropic GW
background by correlating signals of a pair of `advanced' LIGO observatories.Comment: 7 pages, 1 figur
Path-Integral Formulation of Casimir Effects in Supersymmetric Quantum Electrodynamics
The Casimir effect is an interesting phenomenon in the sense that it provides
us with one of the primitive means of extracting the energy out of the vacuum.
Since the original work of Casimir a number of works have appeared in extending
the result to the case of more general topological and dynamical configurations
of the boundary condition and to the circumstances at finite temperature and
gravity. In the studies of the Casimir effects it is common to assume the free
electromagnetic field in the bounded region. It may be interesting to extend
our arguments for fields other than the electromagnetic field. The Casimir
effect due to the free fermionic fields has been investigated by several
authors and has been found to result in an attractive force under the suitable
physical boundary conditions.Comment: 12 pages, 6 figures, REVTe
Confined two-dimensional fermions at finite density
We introduce the chemical potential in a system of two-dimensional massless
fermions, confined to a finite region, by imposing twisted boundary conditions
in the Euclidean time direction. We explore in this simple model the
application of functional techniques which could be used in more complicated
situations.Comment: 15 pages, LaTe
Ricci-Flat and Charged Wormholes in Five Dimensions
We construct stationary Ricci-flat inter-universe Lorentzian wormhole
solutions in all D\ge 5 dimensions that connect two flat asymptotic spacetimes.
Such a solution can be viewed as the gravity dual of a string tachyon state
whose linear momentum is larger than its tension. We focus our analysis on the
D=5 wormholes which are not traversable for the timelike and null geodesics;
however, we demonstrate that there exist accelerated timelike trajectories that
traverse from one asymptotic region to the other. We further study the
minimally-coupled scalar wave equation and demonstrate that the quantum
tunnelling between two worlds must occur. We also obtain charged wormholes in
five-dimensional supergravities. With appropriate choice of parameters, these
wormholes connect AdS in one asymptotic region to flat
Minkowskian spacetime in the other.Comment: Latex, 15 pages, reorganisation of sections, expanded discussion on
accelerated time trajectories and on charged wormholes, references adde
Quark-Meson Coupling Model for a Nucleon
The quark-meson coupling model for a nucleon is considered. The model
describes a nucleon as an MIT bag, in which quarks are coupled to scalar and
vector mesons. A set of coupled equations for the quark and the meson fields
are obtained and are solved in a self-consistent way. It is shown that the mass
of a nucleon as a dressed MIT bag interacting with sigma- and omega-meson
fields significantly differs from the mass of a free MIT bag. A few sets of
model parameters are obtained so that the mass of a dressed MIT bag becomes the
nucleon mass. The results of our calculations imply that the self-energy of the
bag in the quark-meson coupling model is significant and needs to be considered
in doing the nuclear matter calculations.Comment: 3 figure
Symmetry of boundary conditions of the Dirac equation for electrons in carbon nanotubes.
We consider the effective mass model of spinless electrons in single wall carbon nanotubes that is equivalent to the Dirac equation for massless fermions. Within this framework we derive all possible energy independent hard wall boundary conditions that are applicable to metallic tubes. The boundary conditions are classified in terms of their symmetry properties and we demonstrate that the use of different boundary conditions will result in varying degrees of valley degeneracy breaking of the single particle energy spectrum
Bosonic Fields in the String-like Defect Model
We study localization of bosonic bulk fields on a string-like defect with
codimension 2 in a general space-time dimension in detail. We show that in
cases of spin 0 scalar and spin 1 vector fields there are an infinite number of
massless Kaluza-Klein (KK) states which are degenerate with respect to the
radial quantum number, but only the massless zero mode state among them is
coupled to fermion on the string-like defect. It is also commented on
interesting extensions of the model at hand to various directions such as
'little' superstring theory, conformal field theory and a supersymmetric
construction.Comment: 17 pages, LaTex 2e, revised version (to appear in Phys. Rev. D
Finite density and temperature in hybrid bag models
We introduce the chemical potential in a system of two-flavored massless
fermions in a chiral bag by imposing boundary conditions in the Euclidean time
direction. We express the fermionic mean number in terms of a functional trace
involving the Green function of the boundary value problem, which is studied
analytically. Numerical evaluations for the fermionic number are presented.Comment: 19 pages, 4 figure
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