687 research outputs found
Low-energy general relativity with torsion: a systematic derivative expansion
We attempt to build systematically the low-energy effective Lagrangian for
the Einstein--Cartan formulation of gravity theory that generally includes the
torsion field. We list all invariant action terms in certain given order; some
of the invariants are new. We show that in the leading order the fermion action
with torsion possesses additional U(1)_L x U(1)_R gauge symmetry, with 4+4
components of the torsion (out of the general 24) playing the role of Abelian
gauge bosons. The bosonic action quadratic in torsion gives masses to those
gauge bosons. Integrating out torsion one obtains a point-like 4-fermion action
of a general form containing vector-vector, axial-vector and axial-axial
interactions. We present a quantum field-theoretic method to average the
4-fermion interaction over the fermion medium, and perform the explicit
averaging for free fermions with given chemical potential and temperature. The
result is different from that following from the "spin fluid" approach used
previously. On the whole, we arrive to rather pessimistic conclusions on the
possibility to observe effects of the torsion-induced 4-fermion interaction,
although under certain circumstances it may have cosmological consequences.Comment: 33 pages, 1 figure. A new section, discussion and references added.
Final (published) versio
Space-time in light of Karolyhazy uncertainty relation
General relativity and quantum mechanics provide a natural explanation for
the existence of dark energy with its observed value and predict its dynamics.
Dark energy proves to be necessary for the existence of space-time itself and
determines the rate of its stability.Comment: 5 pages, Two misprints are correcte
Low-Energy Effective Action in Non-Perturbative Electrodynamics in Curved Spacetime
We study the heat kernel for the Laplace type partial differential operator
acting on smooth sections of a complex spin-tensor bundle over a generic
-dimensional Riemannian manifold. Assuming that the curvature of the U(1)
connection (that we call the electromagnetic field) is constant we compute the
first two coefficients of the non-perturbative asymptotic expansion of the heat
kernel which are of zero and the first order in Riemannian curvature and of
arbitrary order in the electromagnetic field. We apply these results to the
study of the effective action in non-perturbative electrodynamics in four
dimensions and derive a generalization of the Schwinger's result for the
creation of scalar and spinor particles in electromagnetic field induced by the
gravitational field. We discover a new infrared divergence in the imaginary
part of the effective action due to the gravitational corrections, which seems
to be a new physical effect.Comment: LaTeX, 42 page
Localization of Classical Waves in Weakly Scattering Two-Dimensional Media with Anisotropic Disorder
We study the localization of classical waves in weakly scattering 2D systems
with anisotropic disorder. The analysis is based on a perturbative
path-integral technique combined with a spectral filtering that accounts for
the first-order Bragg scattering only. It is shown that in the long-wavelength
limit the radiation is always localized, and the localization length is
independent of the direction of propagation, the latter in contrast to the
predictions based on an anisotropic tight-binding model. For shorter
wavelengths that are comparable to the correlation scales of the disorder, the
transport properties of disordered media are essentially different in the
directions along and across the correlation ellipse. There exists a
frequency-dependent critical value of the anisotropy parameter, below which
waves are localized at all angles of propagation. Above this critical value,
the radiation is localized only within some angular sectors centered at the
short axis of the correlation ellipse and is extended in other directions.Comment: 10 pages, 5 figure
Non-autonomous Hamiltonian systems related to highest Hitchin integrals
We describe non-autonomous Hamiltonian systems coming from the Hitchin
integrable systems. The Hitchin integrals of motion depend on the W-structures
of the basic curve. The parameters of the W-structures play the role of times.
In particular, the quadratic integrals dependent on the complex structure
(W_2-structure) of the basic curve and times are coordinate on the Teichmuller
space. The corresponding flows are the monodromy preserving equations such as
the Schlesinger equations, the Painleve VI equation and their generalizations.
The equations corresponding to the highest integrals are monodromy preserving
conditions with respect to changing of the W_k-structures (k>2). They are
derived by the symplectic reduction from the gauge field theory on the basic
curve interacting with W_k-gravity. As by product we obtain the classical Ward
identities in this theory.Comment: 21 pages,Latex, Contribution in the Proceedings "International
Seminar on Integrable systems". In memoriam Mikail V. Saveliev. Bonn,
February, 199
The Central Correlations of Hypercharge, Isospin, Colour and Chirality in the Standard Model
The correlation of the fractionally represented hypercharge group with the
isospin and colour group in the standard model determines as faithfully
represented internal group the quotient group
{\U(1)\x\SU(2)\x\SU(3)\over\Z_2\x\Z_3}. The discrete cyclic central
abelian-nonabelian internal correlation involved is considered with respect to
its consequences for the representations by the standard model fields, the
electroweak mixing angle and the symmetry breakdown. There exists a further
discrete -correlation between chirality and Lorentz properties and also a
continuous \U(1)-external-internal one between hyperisospin and chirality.Comment: 18 pages, latex, macros include
Two-loop Euler-Heisenberg effective actions from charged open strings
We present the multiloop partition function of open bosonic string theory in
the presence of a constant gauge field strength, and discuss its low-energy
limit. The result is written in terms of twisted determinants and differentials
on higher-genus Riemann surfaces, for which we provide an explicit
representation in the Schottky parametrization. In the field theory limit, we
recover from the string formula the two-loop Euler-Heisenberg effective action
for adjoint scalars minimally coupled to the background gauge field.Comment: 32 pages, 3 eps figures, plain LaTeX. References added, minor changes
to the text. Published version, affiliation correcte
The Exact Electron Propagator in a Magnetic Field as the Sum over Landau Levels on a Basis of the Dirac Equation Exact Solutions
The exact propagator for an electron in a constant uniform magnetic field as
the sum over Landau levels is obtained by the direct derivation by standard
methods of quantum field theory from exact solutions of the Dirac equation in
the magnetic field. The result can be useful for further development of the
calculation technique of quantum processes in an external active medium,
particularly in the conditions of moderately large field strengths when it is
insufficient to take into account only the ground Landau level contribution.Comment: 9 pages, LaTeX; v2: 3 misprints corrected, a note and 1 reference
added; to appear in Int. J. Mod. Phys.
Spin Relaxation in a Quantized Hall Regime in Presence of a Disorder
We study the spin relaxation (SR) of a two-dimensional electron gas (2DEG) in
the quantized Hall regime and discuss the role of spatial inhomogeneity effects
on the relaxation. The results are obtained for small filling factors () or when the filling factor is close to an integer. In either case SR times
are essentially determined by a smooth random potential. For small we
predict a "magneto-confinement" resonance manifested in the enhancement of the
SR rate when the Zeeman energy is close to the spacing of confinement sublevels
in the low-energy wing of the disorder-broadened Landau level. In the resonant
region the -dependence of the SR time has a peculiar non-monotonic shape. If
, the SR is going non-exponentially. Under typical conditions
the calculated SR times range from to s.Comment: 10 pages, 1 figure. To appear in JETP Letter
Relativistic Coulomb problem for particles with arbitrary half-integer spin
Using relativistic tensor-bispinorial equations proposed in hep-th/0412213 we
solve the Kepler problem for a charged particle with arbitrary half-integer
spin interacting with the Coulomb potential.Comment: Misprints are correcte
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