214 research outputs found
Lepton Mass Effects in Single Pion Production by Neutrinos
We reconsider the Feynman-Kislinger-Ravndal model applied to
neutrino-excitation of baryon resonances. The effects of lepton mass are
included, using the formalism of Kuzmin, Lyubushkin and Naumov. In addition we
take account of the pion-pole contribution to the hadronic axial vector
current. Application of this new formalism to the reaction nu(mu) + p --> mu +
Delta at E(nu) approx 1 GeV gives a suppressed cross section at small angles,
in agreement with the screening correction in Adler's forward scattering
theorem. Application to the process nu(tau) + p --> tau + Delta at E(nu) approx
7 GeV leads to the prediction of right-handed tau polarization for
forward-going leptons, in line with a calculation based on an isobar model. Our
formalism represents an improved version of the Rein-Sehgal model,
incorporating lepton mass effects in a manner consistent with PCAC.Comment: 14 pages, 5 figures. Typos in eq. 9 and 27 corrected. Numbers in
table I for coherent cross sections (RSA and RSC) corrected (normalization
error). Figs 3 and 4 changed accordingly. These corrections also apply to the
published version PRD 76, 113004 (2007
Higher order corrections to the Newtonian potential in the Randall-Sundrum model
The general formalism for calculating the Newtonian potential in fine-tuned
or critical Randall-Sundrum braneworlds is outlined. It is based on using the
full tensor structure of the graviton propagator. This approach avoids the
brane-bending effect arising from calculating the potential for a point source.
For a single brane, this gives a clear understanding of the disputed overall
factor 4/3 entering the correction. The result can be written on a compact form
which is evaluated to high accuracy for both short and large distances.Comment: 12 pages, LaTeX2e with RevTeX4, 3 postscript figures; Minor
corrections, references update
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
Radiative Corrections to the Casimir Energy
The lowest radiative correction to the Casimir energy density between two
parallel plates is calculated using effective field theory. Since the
correlators of the electromagnetic field diverge near the plates, the
regularized energy density is also divergent. However, the regularized integral
of the energy density is finite and varies with the plate separation L as
1/L^7. This apparently paradoxical situation is analyzed in an equivalent, but
more transparent theory of a massless scalar field in 1+1 dimensions confined
to a line element of length L and satisfying Dirichlet boundary conditions.Comment: 7 pages, Late
Multiparticle production in the model with antishadowing
We discuss the role of absorbtion and antishadowing in particle production.
We reproduce power-like energy behavior of the mean multiplicity in the model
with antishadowing and discuss physical implications of such behavior for the
hadron structure.Comment: 11 pages, 3 figures, extended version of the talk at the XXXII
International Symposium on Multiparticle Dynamics September 7-13, 2002
Alushta, Crimea, Ukrain
Zero modes, entropy bounds and partition functions
Some recent finite temperature calculations arising in the investigation of
the Verlinde-Cardy relation are re-analysed. Some remarks are also made about
temperature inversion symmetry.Comment: 12 pages, JyTe
Zeta function method and repulsive Casimir forces for an unusual pair of plates at finite temperature
We apply the generalized zeta function method to compute the Casimir energy
and pressure between an unusual pair of parallel plates at finite temperature,
namely: a perfectly conducting plate and an infinitely permeable one. The high
and low temperature limits of these quantities are discussed; relationships
between high and low temperature limits are estabkished by means of a modified
version of the temperature inversion symmetry.Comment: latex file 9 pages, 3 figure
Worldline path integral for the massive Dirac propagator : A four-dimensional approach
We simplify and generalize an approach proposed by Di Vecchia and Ravndal to
describe a massive Dirac particle in external vector and scalar fields. Two
different path integral representations for the propagator are derived
systematically without the usual five-dimensional extension and shown to be
equivalent due to the supersymmetry of the action. They correspond to a
projection on the mass of the particle either continuously or at the end of the
time evolution. It is shown that the supersymmetry transformations are
generated by shifting and scaling the supertimes and the invariant difference
of two supertimes is given for the general case. A nonrelativistic reduction of
the relativistic propagator leads to a three-dimensional path integral with the
usual Pauli Hamiltonian. By integrating out the photons we obtain the effective
action for quenched QED and use it to derive the gauge-transformation
properties of the general Green function of the theory.Comment: 27 pages, LaTeX, no figures, uses revtex.sty; note with omitted
references added in proo
Equations of Motion of Spinning Relativistic Particle in Electromagnetic and Gravitational Fields
We consider the motion of a spinning relativistic particle in external
electromagnetic and gravitational fields, to first order in the external field,
but to an arbitrary order in spin. The noncovariant spin formalism is crucial
for the correct description of the influence of the spin on the particle
trajectory. We show that the true coordinate of a relativistic spinning
particle is its naive, common coordinate \r. Concrete calculations are
performed up to second order in spin included. A simple derivation is presented
for the gravitational spin-orbit and spin-spin interactions of a relativistic
particle. We discuss the gravimagnetic moment (GM), a specific spin effect in
general relativity. It is shown that for the Kerr black hole the gravimagnetic
ratio, i.e., the coefficient at the GM, equals unity (just as for the charged
Kerr hole the gyromagnetic ratio equals two). The equations of motion obtained
for relativistic spinning particle in external gravitational field differ
essentially from the Papapetrou equations.Comment: 32 pages, latex, Plenary talk at the Fairbank Meeting on the
Lense--Thirring Effect, Rome-Pescara, 29/6-4/7 199
- âŠ