134 research outputs found

### Cosmic acceleration from second order gauge gravity

We construct a phenomenological theory of gravitation based on a second order
gauge formulation for the Lorentz group. The model presents a long-range
modification for the gravitational field leading to a cosmological model
provided with an accelerated expansion at recent times. We estimate the model
parameters using observational data and verify that our estimative for the age
of the Universe is of the same magnitude than the one predicted by the standard
model. The transition from the decelerated expansion regime to the accelerated
one occurs recently (at $\sim9.3\;Gyr$).Comment: RevTex4 15 pages, 1 figure. Accepted for publication in Astrophysics
& Space Scienc

### Quaternion Gravi-Electromagnetism

Defining the generalized charge, potential, current and generalized fields as
complex quantities where real and imaginary parts represent gravitation and
electromagnetism respectively, corresponding field equation, equation of motion
and other quantum equations are derived in manifestly covariant manner. It has
been shown that the field equations are invariant under Lorentz as well as
duality transformations. It has been shown that the quaternionic formulation
presented here remains invariant under quaternion transformations.Comment: Key Words: Quaternion, dyons, gravito-dyons, gravi-electromagnetism.
PACS No.: 04.90. +e ; 14.80. H

### PT-Symmetry Quantum Electrodynamics--PTQED

The construction of $\mathcal{PT}$-symmetric quantum electrodynamics is
reviewed. In particular, the massless version of the theory in 1+1 dimensions
(the Schwinger model) is solved. Difficulties with unitarity of the $S$-matrix
are discussed.Comment: 11 pages, 1 figure, contributed to Proceedings of 6th International
Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physic

### QCD Chiral restoration at finite $T$ under the Magnetic field: Studies based on the instanton vacuum model

We investigate the chiral restoration at finite temperature $(T)$ under the
strong external magnetic field $\vec{B}=B_{0}\hat{z}$ of the SU(2) light-flavor
QCD matter. We employ the instanton-liquid QCD vacuum configuration accompanied
with the linear Schwinger method for inducing the magnetic field. The
Harrington-Shepard caloron solution is used to modify the instanton parameters,
i.e. the average instanton size $(\bar{\rho})$ and inter-instanton distance
$(\bar{R})$, as functions of $T$. In addition, we include the meson-loop
corrections (MLC) as the large-$N_{c}$ corrections because they are critical
for reproducing the universal chiral restoration pattern. We present the
numerical results for the constituent-quark mass as well as chiral condensate
which signal the spontaneous breakdown of chiral-symmetry (SB$\chi$S), as
functions of $T$ and $B$. Besides we find that the changes for the $F_\pi$ and
$m_\pi$ due to the magnetic field is relatively small, in comparison to those
caused by the finite $T$ effect.Comment: 4 pages, 1 table, 6figs. arXiv admin note: significant text overlap
with arXiv:1103.605

### The Casimir Problem of Spherical Dielectrics: Quantum Statistical and Field Theoretical Approaches

The Casimir free energy for a system of two dielectric concentric nonmagnetic
spherical bodies is calculated with use of a quantum statistical mechanical
method, at arbitrary temperature. By means of this rather novel method, which
turns out to be quite powerful (we have shown this to be true in other
situations also), we consider first an explicit evaluation of the free energy
for the static case, corresponding to zero Matsubara frequency ($n=0$).
Thereafter, the time-dependent case is examined. For comparison we consider the
calculation of the free energy with use of the more commonly known field
theoretical method, assuming for simplicity metallic boundary surfaces.Comment: 31 pages, LaTeX, one new reference; version to appear in Phys. Rev.

### What would be outcome of a Big Crunch?

I suggest the existence of a still undiscovered interaction: repulsion
between matter and antimatter. The simplest and the most elegant candidate for
such a force is gravitational repulsion between particles and antiparticles. I
argue that such a force may give birth to a new Universe; by transforming an
eventual Big Crunch of our universe, to an event similar to Big Bang. In fact,
when a collapsing Universe is reduced to a supermassive black hole of a small
size, a very strong field of the conjectured force may create
particle-antiparticle pairs from the surrounding vacuum. The amount of the
antimatter created from the physical vacuum is equal to the decrease of mass of
"black hole Universe" and violently repelled from it. When the size of the
black hole is sufficiently small the creation of antimatter may become so huge
and fast, that matter of our Universe may disappear in a fraction of the Planck
time. So fast transformation of matter to antimatter may look like a Big Bang
with the initial size about 30 orders of magnitude greater than the Planck
length, questioning the need for inflation. In addition, a Big Crunch, of a
Universe dominated by matter, leads to a new Universe dominated by antimatter,
and vice versa; without need to invoke CP violation as explanation of
matter-antimatter asymmetry. Simply, our present day Universe is dominated by
matter, because the previous Universe was dominated by antimatter

### Limits on Production of Magnetic Monopoles Utilizing Samples from the DO and CDF Detectors at the Tevatron

We present 90% confidence level limits on magnetic monopole production at the
Fermilab Tevatron from three sets of samples obtained from the D0 and CDF
detectors each exposed to a proton-antiproton luminosity of $\sim175 {pb}^{-1}$
(experiment E-882). Limits are obtained for the production cross-sections and
masses for low-mass accelerator-produced pointlike Dirac monopoles trapped and
bound in material surrounding the D0 and CDF collision regions. In the absence
of a complete quantum field theory of magnetic charge, we estimate these limits
on the basis of a Drell-Yan model. These results (for magnetic charge values of
1, 2, 3, and 6 times the minimum Dirac charge) extend and improve previously
published bounds.Comment: 18 pages, 17 figures, REVTeX

### Mathematical Tools for Calculation of the Effective Action in Quantum Gravity

We review the status of covariant methods in quantum field theory and quantum
gravity, in particular, some recent progress in the calculation of the
effective action via the heat kernel method. We study the heat kernel
associated with an elliptic second-order partial differential operator of
Laplace type acting on smooth sections of a vector bundle over a Riemannian
manifold without boundary. We develop a manifestly covariant method for
computation of the heat kernel asymptotic expansion as well as new algebraic
methods for calculation of the heat kernel for covariantly constant background,
in particular, on homogeneous bundles over symmetric spaces, which enables one
to compute the low-energy non-perturbative effective action.Comment: 71 pages, 2 figures, submitted for publication in the Springer book
(in preparation) "Quantum Gravity", edited by B. Booss-Bavnbek, G. Esposito
and M. Lesc

### A nondiagrammatic calculation of the Rho parameter from heavy fermions

A simple nondiagrammatic evaluation of the nondecoupling effect of heavy
fermions on the Veltman's Rho parameter is presented in detail. This
calculation is based on the path integral approach, the electroweak chiral
Lagrangian formalism, and the Schwinger proper time method.Comment: 11 page

### A differential identity for Green functions

If P is a differential operator with constant coefficients, an identity is
derived to calculate the action of exp(P) on the product of two functions. In
many-body theory, P describes the interaction Hamiltonian and the identity
yields a hierarchy of Green functions. The identity is first derived for scalar
fields and the standard hierarchy is recovered. Then the case of fermions is
considered and the identity is used to calculate the generating function for
the Green functions of an electron system in a time-dependent external
potential.Comment: 14 page

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