38,824 research outputs found
The analytical discussion on strong gravitaional lensing for a gravitational source with a global monopole
Here the gravitational lensing in strong field limit of a Schwarzschild black
hole with a solid deficit angle owing to global monopole within the context of
the gravity theory is investigated. We obtain the expressions of
deflection angle and time delay in the forms of elliptic integrals and discuss
the asymptotic behaviour of the elliptic integrals to find the explicit
formulae of angle and time difference in the strong field limit. We show that
the deflection angle and the time delay between multiple images are related not
only to the monopole but also to the correction by taking the
cosmological boundary into account. Some observables such as the minimum impact
parameter, the angular separation, the relative magnification and the compacted
angular position have been estimated as well. It is intriguing that the tiny
modification on the standard general relativity will make the remarkable
deviation on the angle and the time lag, offering a significant way to explore
some possible distinct signatures of the topological soliton and the correction
of the Einstein general relativity.Comment: 11 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1004.342
Finite Temperature Casimir Effect and Dispersion in the Presence of Compactified Extra Dimensions
Finite temperature Casimir theory of the Dirichlet scalar field is developed,
assuming that there is a conventional Casimir setup in physical space with two
infinitely large plates separated by a gap R and in addition an arbitrary
number q of extra compacified dimensions. As a generalization of earlier
theory, we assume in the first part of the paper that there is a scalar
'refractive index' N filling the whole of the physical space region. After
presenting general expressions for free energy and Casimir forces we focus on
the low temperature case, as this is of main physical interest both for force
measurements and also for issues related to entropy and the Nernst theorem.
Thereafter, in the second part we analyze dispersive properties, assuming for
simplicity q=1, by taking into account dispersion associated with the first
Matsubara frequency only. The medium-induced contribution to the free energy,
and pressure, is calculated at low temperatures.Comment: 25 pages, one figure. Minor changes in the discussion. Version to
appear in Physica Script
Electron-positron pair production in the electrosphere of quark stars
We study Schwinger pair creation of charged particles due to the
inhomogeneous electric field created by the thin electron layer at the surface
of quark stars (the electrosphere). As suggested earlier, due to the low photon
emissivity of the quark-gluon plasma and of the electrosphere,
electron-positron pair emission could be the main observational signature of
quark stars. To obtain the electron-positron pair creation rate we use the
tunnelling approach. Explicit expressions for the fermion creation rate per
unit time per unit volume are derived, which generalize the classical Schwinger
result. The finite size effects in pair production, due to the presence of a
boundary (the surface of the quark star), are also considered in the framework
of a simple approach. It is shown that the boundary effects induce large
quantitative and qualitative deviations of the particle production rate from
what one deduces with the Schwinger formula and its generalization for the
electric field of the electrosphere. The electron-positron pair emissivity and
flux of the electrosphere of quark stars due to pair creation is considered,
and the magnitude of the boundary effects for this parameters is estimated. Due
to the inhomogeneity of the electric field distribution in the electrosphere
and of the presence of the boundary effects, at high temperatures ( MeV) we find a lower electron-positron flux as previously
estimated. The numerical value of the critical temperature depends on
the surface potential of the star. We briefly consider the effect of the
magnetic field on the pair creation process and show that the magnetic field
can enhance drastically the pair creation rate.Comment: 34 pages, 12 figures, accepted for publication in Ap
Squeezed States of the Generalized Minimum Uncertainty State for the Caldirola-Kanai Hamiltonian
We show that the ground state of the well-known pseudo-stationary states for
the Caldirola-Kanai Hamiltonian is a generalized minimum uncertainty state,
which has the minimum allowed uncertainty , where is a constant depending on the damping
factor and natural frequency. The most general symmetric Gaussian states are
obtained as the one-parameter squeezed states of the pseudo-stationary ground
state. It is further shown that the coherent states of the pseudo-stationary
ground state constitute another class of the generalized minimum uncertainty
states.Comment: RevTex4, 9 pages, no fingure; to be published in Journal of Physics
H_c_3 for a thin-film superconductor with a ferromagnetic dot
We investigate the effect of a ferromagnetic dot on a thin-film
superconductor. We use a real-space method to solve the linearized
Ginzburg-Landau equation in order to find the upper critical field, H_c_3. We
show that H_c_3 is crucially dependent on dot composition and geometry, and may
be significantly greater than H_c_2. H_c_3 is maximally enhanced when (1) the
dot saturation magnetization is large, (2) the ratio of dot thickness to dot
diameter is of order one, and (3) the dot thickness is large
Effect of gauge boson mass on chiral symmetry breaking in QED
In three-dimensional quantum electrodynamics (QED) with massive gauge
boson, we investigate the Dyson-Schwinger equation for the fermion self-energy
in the Landau gauge and find that chiral symmetry breaking (CSB) occurs when
the gauge boson mass is smaller than a finite critical value
but is suppressed when . We further show that the critical
value does not qualitatively change after considering higher order
corrections from the wave function renormalization and vertex function. Based
on the relation between CSB and the gauge boson mass , we give a field
theoretical description of the competing antiferromagnetic and superconducting
orders and, in particular, the coexistence of these two orders in high
temperature superconductors. When the gauge boson mass is generated via
instanton effect in a compact QED of massless fermions, our result shows
that CSB coexists with instanton effect in a wide region of , which can be
used to study the confinement-deconfinement phase transition.Comment: 34 pagess, 2 figure
Exclusive Hadronic D Decays to eta' and eta
Hadronic decay modes and
are studied in the generalized
factorization approach. Form factors for transitions
are carefully evaluated by taking into account the wave function normalization
of the eta and eta'. The predicted branching ratios are generally in agreement
with experiment except for and
; the calculated decay rates for the first two decay modes
are too small by an order of magnitude. We show that the weak decays and followed by resonance-induced final-state
interactions (FSI), which are amenable technically, are able to enhance the
branching ratios of and dramatically
without affecting the agreement between theory and experiment for and . We argue that it is difficult to understand
the observed large decay rates of and
simultaneously; FSI, W-annihilation and the production of excess eta' from
gluons are not helpful in this regard. The large discrepancy between the
factorization hypothesis and experiment for the ratio of
and remains as an enigma.Comment: 15 pages, 1 figure, to appear in Phys. Rev. D. Form factors for D to
eta and eta' transitions are slightly change
Universality properties of the stationary states in the one-dimensional coagulation-diffusion model with external particle input
We investigate with the help of analytical and numerical methods the reaction
A+A->A on a one-dimensional lattice opened at one end and with an input of
particles at the other end. We show that if the diffusion rates to the left and
to the right are equal, for large x, the particle concentration c(x) behaves
like As/x (x measures the distance to the input end). If the diffusion rate in
the direction pointing away from the source is larger than the one
corresponding to the opposite direction the particle concentration behaves like
Aa/sqrt(x). The constants As and Aa are independent of the input and the two
coagulation rates. The universality of Aa comes as a surprise since in the
asymmetric case the system has a massive spectrum.Comment: 27 pages, LaTeX, including three postscript figures, to appear in J.
Stat. Phy
Minimal Flavour Violation and Beyond
Starting from the effective-theory framework for Minimal Flavour Violation,
we give a systematic definition of next-to-minimal (quark) flavour violation in
terms of a set of spurion fields exhibiting a particular hierarchy with respect
to a small (Wolfenstein-like) parameter. A few illustrative examples and their
consequences for charged and neutral decays with different quark chiralities
are worked out in some detail. Our framework can be used as a model-independent
classification scheme for the parameterization of flavour structure from
physics beyond the Standard Model.Comment: 17 pages, no figures, phenomenological discussion extended,
references adde
- …