724 research outputs found
QFT results for neutrino oscillations and New Physics
The CP asymmetry in neutrino oscillations, assuming new physics at production
and/or detection processes, is analyzed. We compute this CP asymmetry using the
standard quantum field theory within a general new physics scenario that may
generate new sources of CP and flavor violation. Well known results for the CP
asymmetry are reproduced in the case of V -A operators, and additional
contributions from new physics operators are derived. We apply this formalism
to SUSY extensions of the Standard Model where the contributions from new
operators could produce a CP asymmetry observable in the next generation of
neutrino experiments.Comment: 6 pages, 3 figures, version to be published in Phys.Rev.
Polarization of Instantons and Gravity
Gravity can arise in a conventional non-Abelian gauge theory in which a
specific phenomenon takes place. Suppose there is a condensation of polarized
instantons and antiinstantons in the vacuum state. Then the excitations of the
gauge field in the classical approximation are described through the variables
of Riemann geometry satisfying the Einstein equations of general relativity.
There are no dimensional coupling constants in the theory.Comment: 3 page
Compressible hydromagnetic nonlinearities in the predecoupling plasma
The adiabatic inhomogeneities of the scalar curvature lead to a compressible
flow affecting the dynamics of the hydromagnetic nonlinearities. The influence
of the plasma on the evolution of a putative magnetic field is explored with
the aim of obtaining an effective description valid for sufficiently large
scales. The bulk velocity of the plasma, computed in the framework of the
LambdaCDM scenario, feeds back into the evolution of the magnetic power spectra
leading to a (nonlocal) master equation valid in Fourier space and similar to
the ones discussed in the context of wave turbulence. Conversely, in physical
space, the magnetic power spectra obey a Schroedinger-like equation whose
effective potential depends on the large-scale curvature perturbations.
Explicit solutions are presented both in physical space and in Fourier space.
It is argued that curvature inhomogeneities, compatible with the WMAP 7yr data,
shift to lower wavenumbers the magnetic diffusivity scale.Comment: 29 page
Evidence for topological nonequilibrium in magnetic configurations
We use direct numerical simulations to study the evolution, or relaxation, of
magnetic configurations to an equilibrium state. We use the full single-fluid
equations of motion for a magnetized, non-resistive, but viscous fluid; and a
Lagrangian approach is used to obtain exact solutions for the magnetic field.
As a result, the topology of the magnetic field remains unchanged, which makes
it possible to study the case of topological nonequilibrium. We find two cases
for which such nonequilibrium appears, indicating that these configurations may
develop singular current sheets.Comment: 10 pages, 5 figure
1/N_c corrections to the magnetic susceptibility of the QCD vacuum
We investigate the magnetic susceptibility of the QCD vacuum with the
corrections taken into account, based on the instanton vacuum. Starting from
the instanton liquid model we derive the gauged light-quark partition function
in the presence of the current quark mass as well as of external Abelian vector
and tensor fields. We consider the meson-loop corrections which are
shown to contribute to the magnetic susceptibility by around 15% for the up
(and down) quarks. We also take into account the tensor terms of the
quark-quark interaction from the instanton vacuum as well as the finite-width
effects, both of which are of order . The effects of the
tensor terms and finite width turn out to be negligibly small. The final
results for the up-quarks are given as: with the quark condensate . We also
discuss the pion mass dependence of the magnetic susceptibility in order to
give a qualitative guideline for the chiral extrapolation of lattice data.Comment: 18 pages, 5 figures. Final version to appear in Phys. Rev.
Rapid dissipation of magnetic fields due to Hall current
We propose a mechanism for the fast dissipation of magnetic fields which is
effective in a stratified medium where ion motions can be neglected. In such a
medium, the field is frozen into the electrons and Hall currents prevail.
Although Hall currents conserve magnetic energy, in the presence of density
gradients, they are able to create current sheets which can be the sites for
efficient dissipation of magnetic fields. We recover the frequency,
, for Hall oscillations modified by the presence of density
gradients. We show that these oscillations can lead to the exchange of energy
between different components of the field. We calculate the time evolution and
show that magnetic fields can dissipate on a timescale of order
. This mechanism can play an important role for magnetic
dissipation in systems with very steep density gradients where the ions are
static such as those found in the solid crust of neutron stars.Comment: 9 pages, changed fig.
A Note on the Cosmological Dynamics in Finite-Range Gravity
In this note we consider the homogeneous and isotropic cosmology in the
finite-range gravity theory recently proposed by Babak and Grishchuk. In this
scenario the universe undergoes late time accelerated expansion if both the
massive gravitons present in the model are tachyons. We carry out the phase
space analysis of the system and show that the late-time acceleration is an
attractor of the model.Comment: RevTex, 4 pages, two figures, New references added, To appear in
IJMP
Multiloop calculations in supersymmetric theories with the higher covariant derivative regularization
Most calculations of quantum corrections in supersymmetric theories are made
with the dimensional reduction, which is a modification of the dimensional
regularization. However, it is well known that the dimensional reduction is not
self-consistent. A consistent regularization, which does not break the
supersymmetry, is the higher covariant derivative regularization. However, the
integrals obtained with this regularization can not be usually calculated
analytically. We discuss application of this regularization to the calculations
in supersymmetric theories. In particular, it is demonstrated that integrals
defining the beta-function are possibly integrals of total derivatives. This
feature allows to explain the origin of the exact NSVZ beta-function, relating
the beta-function with the anomalous dimensions of the matter superfields.
However, integrals for the anomalous dimension should be calculated
numerically.Comment: 8 pages, contribution to ACAT 2011 proceeding
Numerical evidence of chiral magnetic effect in lattice gauge theory
The chiral magnetic effect is the generation of electric current of quarks
along external magnetic field in the background of topologically nontrivial
gluon fields. There is a recent evidence that this effect is observed by the
STAR Collaboration in heavy ion collisions at RHIC. In our paper we study
qualitative signatures of the chiral magnetic effect using quenched lattice
simulations. We find indications that the electric current is indeed enhanced
in the direction of the magnetic field both in equilibrium configurations of
the quantum gluon fields and in a smooth gluon background with nonzero
topological charge. In the confinement phase the magnetic field enhances the
local fluctuations of both the electric charge and chiral charge densities. In
the deconfinement phase the effects of the magnetic field become smaller,
possibly due to thermal screening. Using a simple model of a fireball we obtain
a good agreement between our data and experimental results of the STAR
Collaboration.Comment: 14 pages, 14 figures, uses RevTeX 4.0; revision: references and
comments added, figures corrected, published versio
Dynamics of a many-particle Landau-Zener model: inverse sweep
We consider dynamics of a slowly time-dependent Dicke model, which represents
a many-body generalization of the Landau-Zener model. In particular, the model
describes narrow Feshbach resonance passage in an ultracold gas of Fermi atoms.
Adiabaticity is destroyed when a parameter crosses a critical value, even at
very slow sweeping rates of a parameter. The dynamics crucially depends on
direction of the sweep. We apply our recent analysis [A.P. Itin, P. Torma,
arXiv:0901.4778v1] to the "inverse" sweep through the resonance, corresponding
(in a context of Feshbach resonance passage) to dissociation of molecules. On a
level of the mean-field approximation, the dynamics is equivalent to a
molecular condensate formation from Bose atoms within a two-mode model. Mapping
the system to a Painlev\'e equation allows us to calculate deviation from
adiabaticity at very slow sweeps analytically.Comment: 3 pages. Submitted to CEWQO 2009 on 14th Februar
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