443 research outputs found
Particle dynamics in a class of 2-dimensional gravity theories
We provide a method to determine the motion of a classical massive particle
in a background geometry of 2-dimensional gravity theories, for which the
Birkhoff theorem holds. In particular, we get the particle trajectory in a
continuous class of 2-dimensional dilaton gravity theories that includes the
Callan-Giddings-Harvey-Strominger (CGHS) model, the Jackiw-Teitelboim (JT)
model, and the -dimensional -wave Einstein gravity. The explicit
trajectory expressions for these theories are given along with the discussions
on the results.Comment: 15 pages, LaTeX. The deletion of the repeated portion of the abstract
and the proper line wrapping of the tex file. No other change
Gauge-ready formulation of the cosmological kinetic theory in generalized gravity theories
We present cosmological perturbations of kinetic components based on
relativistic Boltzmann equations in the context of generalized gravity
theories. Our general theory considers an arbitrary number of scalar fields
generally coupled with the gravity, an arbitrary number of mutually interacting
hydrodynamic fluids, and components described by the relativistic Boltzmann
equations like massive/massless collisionless particles and the photon with the
accompanying polarizations. We also include direct interactions among fluids
and fields. The background FLRW model includes the general spatial curvature
and the cosmological constant. We consider three different types of
perturbations, and all the scalar-type perturbation equations are arranged in a
gauge-ready form so that one can implement easily the convenient gauge
conditions depending on the situation. In the numerical calculation of the
Boltzmann equations we have implemented four different gauge conditions in a
gauge-ready manner where two of them are new. By comparing solutions solved
separately in different gauge conditions we can naturally check the numerical
accuracy.Comment: 26 pages, 9 figures, revised thoroughly, to appear in Phys. Rev.
Hypersurface-Invariant Approach to Cosmological Perturbations
Using Hamilton-Jacobi theory, we develop a formalism for solving
semi-classical cosmological perturbations which does not require an explicit
choice of time-hypersurface. The Hamilton-Jacobi equation for gravity
interacting with matter (either a scalar or dust field) is solved by making an
Ansatz which includes all terms quadratic in the spatial curvature.
Gravitational radiation and scalar perturbations are treated on an equal
footing. Our technique encompasses linear perturbation theory and it also
describes some mild nonlinear effects. As a concrete example of the method, we
compute the galaxy-galaxy correlation function as well as large-angle microwave
background fluctuations for power-law inflation, and we compare with recent
observations.Comment: 51 pages, Latex 2.09 ALBERTA THY/20-94, DAMTP R94/25 To appear in
Phys. Rev.
Projecting the Bethe-Salpeter Equation onto the Light-Front and back: A Short Review
The technique of projecting the four-dimensional two-body Bethe-Salpeter
equation onto the three-dimensional Light-Front hypersurface, combined with the
quasi-potential approach, is briefly illustrated, by placing a particular
emphasis on the relation between the projection method and the effective
dynamics of the valence component of the Light-Front wave function. Some
details on how to construct the Fock expansion of both i) the Light-Front
effective interaction and ii) the electromagnetic current operator, satisfying
the proper Ward-Takahashi identity, will be presented, addressing the relevance
of the Fock content in the operators living onto the Light-Front hypersurface.
Finally, the generalization of the formalism to the three-particle case will
be outlined.Comment: 16 pages, macros included. Mini-review to be printed in a regular
issue of Few-Body Systems devoted to the Workshop on "Relativistic
Description of Two- and Three-body Systems in Nuclear Physics" ECT* Trento,
19 - 23 October 200
Work function changes in the double layered manganite La1.2Sr1.8Mn2O7
We have investigated the behaviour of the work function of La1.2Sr1.8Mn2O7 as
a function of temperature by means of photoemission. We found a decrease of 55
+/- 10 meV in going from 60 K to just above the Curie temperature (125 K) of
the sample. Above T_C the work function appears to be roughly constant. Our
results are exactly opposite to the work function changes calculated from the
double-exchange model by Furukawa, but are consistent with other measurements.
The disagreement with double-exchange can be explained using a general
thermodynamic relation valid for second order transitions and including the
extra processes involved in the manganites besides double-exchange interaction.Comment: 6 pages, 4 figures included in tex
Augmented Superfield Approach To Unique Nilpotent Symmetries For Complex Scalar Fields In QED
The derivation of the exact and unique nilpotent Becchi-Rouet-Stora-Tyutin
(BRST)- and anti-BRST symmetries for the matter fields, present in any
arbitrary interacting gauge theory, has been a long-standing problem in the
framework of superfield approach to BRST formalism. These nilpotent symmetry
transformations are deduced for the four (3 + 1)-dimensional (4D) complex
scalar fields, coupled to the U(1) gauge field, in the framework of augmented
superfield formalism. This interacting gauge theory (i.e. QED) is considered on
a six (4, 2)-dimensional supermanifold parametrized by four even spacetime
coordinates and a couple of odd elements of the Grassmann algebra. In addition
to the horizontality condition (that is responsible for the derivation of the
exact nilpotent symmetries for the gauge field and the (anti-)ghost fields), a
new restriction on the supermanifold, owing its origin to the (super) covariant
derivatives, has been invoked for the derivation of the exact nilpotent
symmetry transformations for the matter fields. The geometrical interpretations
for all the above nilpotent symmetries are discussed, too.Comment: LaTeX file, 17 pages, journal versio
Hall Effect and Resistivity in High-Tc Superconductors: The Conserving Approximation
The Hall coefficient (R_H) of high-Tc cuprates in the normal state shows the
striking non-Fermi liquid behavior: R_H follows a Curie-Weiss type temperature
dependence, and |R_H|>>1/|ne| at low temperatures in the under-doped compounds.
Moreover, R_H is positive for hole-doped compounds and is negative for
electron-doped ones, although each of them has a similar hole-like Fermi
surface. In this paper, we give the explanation of this long-standing problem
from the standpoint of the nearly antiferromagnetic (AF) Fermi liquid. We
consider seriously the vertex corrections for the current which are
indispensable to satisfy the conservation laws, which are violated within the
conventional Boltzmann transport approximation. The obtained total current J_k
takes an enhanced value and is no more perpendicular to the Fermi surface due
to the strong AF fluctuations. By virtue of this mechanism, the anomalous
behavior of R_H in high-Tc cuprates is neutrally explained. We find that both
the temperature and the (electron, or hole) doping dependences of R_H in
high-T_c cuprates are reproduced well by numerical calculations based on the
fluctuation-exchange (FLEX) approximation, applied to the single-band Hubbard
model. We also discuss the temperature dependence of R_H in other nearly AF
metals, e.g., V_2O_3, kappa-BEDT-TTF organic superconductors, and heavy fermion
systems close to the AF phase boundary.Comment: 19 pages, to appear in Phys. Rev. B, No.59, Vol.22, 199
Absolutely anticommuting (anti-)BRST symmetry transformations for topologically massive Abelian gauge theory
We demonstrate the existence of the nilpotent and absolutely anticommuting
Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST symmetry transformations for the
four (3 + 1)-dimensional (4D) topologically massive Abelian U(1) gauge theory
that is described by the coupled Lagrangian densities (which incorporate the
celebrated (B \wedge F) term). The absolute anticommutativity of the (anti-)
BRST symmetry transformations is ensured by the existence of a Curci-Ferrari
type restriction that emerges from the superfield formalism as well as from the
equations of motion that are derived from the above coupled Lagrangian
densities. We show the invariance of the action from the point of view of the
symmetry considerations as well as superfield formulation. We discuss,
furthermore, the topological term within the framework of superfield formalism
and provide the geometrical meaning of its invariance under the (anti-) BRST
symmetry transformations.Comment: LaTeX file, 22 pages, journal versio
Density perturbations in generalized Einstein scenarios and constraints on nonminimal couplings from the Cosmic Microwave Background
We study cosmological perturbations in generalized Einstein scenarios and
show the equivalence of inflationary observables both in the Jordan frame and
the Einstein frame. In particular the consistency relation relating the
tensor-to-scalar ratio with the spectral index of tensor perturbations
coincides with the one in Einstein gravity, which leads to the same likelihood
results in terms of inflationary observables. We apply this formalism to
nonminimally coupled chaotic inflationary scenarios with potential
and place constraints on the strength of nonminimal couplings using a
compilation of latest observational data. In the case of the quadratic
potential (), the nonminimal coupling is constrained to be for negative from the observational contour
bound. Although the quartic potential () is under a strong observational
pressure for , this property is relaxed by taking into account negative
nonminimal couplings. We find that inflationary observables are within the
contour bound as long as . We also show that
the cases are disfavoured even in the presence of nonminimal
couplings.Comment: 16 pages, 4 eps figure
Angle-resolved photoemission in doped charge-transfer Mott insulators
A theory of angle-resolved photoemission (ARPES) in doped cuprates and other
charge-transfer Mott insulators is developed taking into account the realistic
(LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon
interaction, and a random field potential. In most of these materials the first
band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the
coherent part of the ARPES spectra with the oxygen hole spectral function
calculated in the non-crossing (ladder) approximation and with the exact
spectral function of a one-dimensional hole in a random potential. Some unusual
features of ARPES including the polarisation dependence and spectral shape in
YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or
small. The theory is compatible with the doping dependence of kinetic and
thermodynamic properties of cuprates as well as with the d-wave symmetry of the
superconducting order parameter.Comment: 8 pages (RevTeX), 10 figures, submitted to Phys. Rev.
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