737 research outputs found
United States-Mexican negotiations in context with United States Extended Jurisdiction Policy
Semiclassical Quantization of Effective String Theory and Regge Trajectories
We begin with an effective string theory for long distance QCD, and evaluate
the semiclassical expansion of this theory about a classical rotating string
solution, taking into account the the dynamics of the boundary of the string.
We show that, after renormalization, the zero point energy of the string
fluctuations remains finite when the masses of the quarks on the ends of the
string approach zero. The theory is then conformally invariant in any spacetime
dimension D. For D=26 the energy spectrum of the rotating string formally
coincides with that of the open string in classical Bosonic string theory.
However, its physical origin is different. It is a semiclassical spectrum of an
effective string theory valid only for large values of the angular momentum.
For D=4, the first semiclassical correction adds the constant 1/12 to the
classical Regge formula.Comment: 65 pages, revtex, 3 figures, added 2 reference
Nonmonotonic dependence of the absolute entropy on temperature in supercooled Stillinger-Weber silicon
Using a recently developed thermodynamic integration method, we compute the
precise values of the excess Gibbs free energy (G^e) of the high density liquid
(HDL) phase with respect to the crystalline phase at different temperatures (T)
in the supercooled region of the Stillinger-Weber (SW) silicon [F. H.
Stillinger and T. A. Weber, Phys. Rev. B. 32, 5262 (1985)]. Based on the slope
of G^e with respect to T, we find that the absolute entropy of the HDL phase
increases as its enthalpy changes from the equilibrium value at T \ge 1065 K to
the value corresponding to a non-equilibrium state at 1060 K. We find that the
volume distribution in the equilibrium HDL phases become progressively broader
as the temperature is reduced to 1060 K, exhibiting van-der-Waals (VDW) loop in
the pressure-volume curves. Our results provides insight into the thermodynamic
cause of the transition from the HDL phase to the low density phases in SW
silicon, observed in earlier studies near 1060 K at zero pressure.Comment: This version is accepted for publication in Journal of Statistical
Physics (11 figures, 1 table
The physical meaning of the de Sitter invariants
We study the Lie algebras of the covariant representations transforming the
matter fields under the de Sitter isometries. We point out that the Casimir
operators of these representations can be written in closed forms and we deduce
how their eigenvalues depend on the field's rest energy and spin. For the
scalar, vector and Dirac fields, which have well-defined field equations, we
express these eigenvalues in terms of mass and spin obtaining thus the
principal invariants of the theory of free fields on the de Sitter spacetime.
We show that in the flat limit we recover the corresponding invariants of the
Wigner irreducible representations of the Poincare group.Comment: 22 pages no figure
Primordial gravitational waves in inflationary braneworld
We study primordial gravitational waves from inflation in Randall-Sundrum
braneworld model. The effect of small change of the Hubble parameter during
inflation is investigated using a toy model given by connecting two de Sitter
branes. We analyze the power spectrum of final zero-mode gravitons, which is
generated from the vacuum fluctuations of both initial Kaluza-Klein modes and
zero-mode. The amplitude of fluctuations is confirmed to agree with the
four-dimensional one at low energies, whereas it is enhanced due to the
normalization factor of zero-mode at high energies. We show that the
five-dimensional spectrum can be well approximated by applying a simple mapping
to the four-dimensional fluctuation amplitude.Comment: 16 pages, 4 figures, typos correcte
Vortices and extreme black holes: the question of flux expulsion
It has been claimed that extreme black holes exhibit a phenomenon of flux
expulsion for abelian Higgs vortices, irrespective of the relative width of the
vortex to the black hole. Recent work by two of the authors showed a subtlety
in the treatment of the event horizon, which cast doubt on this claim. We
analyse in detail the vortex/extreme black hole system, showing that while flux
expulsion can occur, it does not do so in all cases. We give analytic proofs
for both expulsion and penetration of flux, in each case deriving a bound for
that behaviour. We also present extensive numerical work backing up, and
refining, these claims, and showing in detail how a vortex can end on a black
hole in all situations. We also calculate the backreaction of the vortex on the
geometry, and comment on the more general vortex-black hole system.Comment: 28 pages revtex, 10 figures, minor changes, reference adde
Generalized Chaplygin gas model: Cosmological consequences and statefinder diagnosis
The generalized Chaplygin gas (GCG) model in spatially flat universe is
investigated. The cosmological consequences led by GCG model including the
evolution of EoS parameter, deceleration parameter and dimensionless Hubble
parameter are calculated. We show that the GCG model behaves as a general
quintessence model. The GCG model can also represent the pressureless CDM model
at the early time and cosmological constant model at the late time. The
dependency of transition from decelerated expansion to accelerated expansion on
the parameters of model is investigated. The statefinder parameters and
in this model are derived and the evolutionary trajectories in plane are
plotted. Finally, based on current observational data, we plot the evolutionary
trajectories in and planes for best fit values of the parameters of
GCG model. It has been shown that although, there are similarities between GCG
model and other forms of chaplygin gas in statefinder plane, but the distance
of this model from the CDM fixed point in diagram is shorter
compare with standard chaplygin gas model.Comment: 10 pages, 5 figures, accepted in Astrophys Space Sci. (2011
Delocalization in harmonic chains with long-range correlated random masses
We study the nature of collective excitations in harmonic chains with masses
exhibiting long-range correlated disorder with power spectrum proportional to
, where is the wave-vector of the modulations on the random
masses landscape. Using a transfer matrix method and exact diagonalization, we
compute the localization length and participation ratio of eigenmodes within
the band of allowed energies. We find extended vibrational modes in the
low-energy region for . In order to study the time evolution of an
initially localized energy input, we calculate the second moment of
the energy spatial distribution. We show that , besides being dependent
of the specific initial excitation and exhibiting an anomalous diffusion for
weakly correlated disorder, assumes a ballistic spread in the regime
due to the presence of extended vibrational modes.Comment: 6 pages, 9 figure
A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions
Scintillating crystal detector may offer some potential advantages in the
low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed
near the core of Nuclear Power Station II in Taiwan is being constructed for
the studies of electron-neutrino scatterings and other keV-MeV range neutrino
interactions. The motivations of this detector approach, the physics to be
addressed, the basic experimental design, and the characteristic performance of
prototype modules are described. The expected background channels and their
experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method
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