1,410 research outputs found

### The Matsubara-Fradkin Thermodynamical Quantization of Podolsky Electrodynamics

In this work we apply the Matsubara-Fradkin formalism and the Nakanishi's
auxiliary field method to the quantization of the Podolsky electrodynamics in
thermodynamic equilibrium. This approach allows us to write consistently the
path integral representation for the partition function of gauge theories in a
simple manner. Furthermore, we find the Dyson-Schwinger-Fradkin equations and
the Ward-Fradkin-Takahashi identities for the Podolsky theory. We also write
the most general form for the polarization tensor in thermodynamic equilibrium.Comment: Submitted to Physical Review

### Heat transport through quantum Hall edge states: Tunneling versus capacitive coupling to reservoirs

We study the heat transport along an edge state of a two-dimensional electron
gas in the quantum Hall regime, in contact to two reservoirs at different
temperatures. We consider two exactly solvable models for the edge state
coupled to the reservoirs. The first one corresponds to filling $\nu=1$ and
tunneling coupling to the reservoirs. The second one corresponds to integer or
fractional filling of the sequence $\nu=1/m$ (with $m$ odd), and capacitive
coupling to the reservoirs. In both cases we solve the problem by means of
non-equilibrium Green function formalism. We show that heat propagates chirally
along the edge in the two setups. We identify two temperature regimes, defined
by $\Delta$, the mean level spacing of the edge. At low temperatures, $T<
\Delta$, finite size effects play an important role in heat transport, for both
types of contacts. The nature of the contacts manifest themselves in different
power laws for the thermal conductance as a function of the temperature. For
capacitive couplings a highly non-universal behavior takes place, through a
prefactor that depends on the length of the edge as well as on the coupling
strengths and the filling fraction. For larger temperatures, $T>\Delta$,
finite-size effects become irrelevant, but the heat transport strongly depends
on the strength of the edge-reservoir interactions, in both cases. The thermal
conductance for tunneling coupling grows linearly with $T$, whereas for the
capacitive case it saturates to a value that depends on the coupling strengths
and the filling factors of the edge and the contacts.Comment: 15 pages, 5 figure

### Photon and electron spectra in hot and dense QED

Photon and electron spectra in hot and dense QED are found in the high
temperature limit for all |\q| using the Feynman gauge and the one-loop
self-energy. All spectra are split by the medium and their branches develop the
gap (the dynamical mass) at zero momentum. The photon spectrum has two branches
(longitudinal and transverse) with the common mass; but electron spectrum is
split on four branches which are well-separated for any |\q| including their
|\q|=0 limits (their effective masses). These masses and the photon thermal
mass are calculated explicitly and the different limits of spectrum branches
are established in detail. The gauge invariance of the high-temperature spectra
is briefly discussed.Comment: 9 pages, latex, no figure

### The imbalanced antiferromagnet in an optical lattice

We study the rich properties of the imbalanced antiferromagnet in an optical
lattice. We present its phase diagram, discuss spin waves and explore the
emergence of topological excitations in two dimensions, known as merons, which
are responsible for a Kosterlitz-Thouless transition that has never
unambiguously been observed.Comment: 4 pages, 5 figures, RevTe

### Polaron action for multimode dispersive phonon systems

Path-integral approach to the tight-binding polaron is extended to multiple
optical phonon modes of arbitrary dispersion and polarization. The non-linear
lattice effects are neglected. Only one electron band is considered. The
electron-phonon interaction is of the density-displacement type, but can be of
arbitrary spatial range and shape. Feynman's analytical integration of ion
trajectories is performed by transforming the electron-ion forces to the basis
in which the phonon dynamical matrix is diagonal. The resulting polaron action
is derived for the periodic and shifted boundary conditions in imaginary time.
The former can be used for calculating polaron thermodynamics while the latter
for the polaron mass and spectrum. The developed formalism is the analytical
basis for numerical analysis of such models by path-integral Monte Carlo
methods.Comment: 9 page

### Worldsheet Form Factors in AdS/CFT

We formulate a set of consistency conditions appropriate to worldsheet form
factors in the massive, integrable but non-relativistic, light-cone gauge fixed
AdS(5) x S**5 string theory. We then perturbatively verify that these
conditions hold, at tree level in the near-plane-wave limit and to one loop in
the near-flat (Maldacena-Swanson) limit, for a number of specific cases. We
further study the form factors in the weakly coupled dual description,
verifying that the relevant conditions naturally hold for the one-loop
Heisenberg spin-chain. Finally, we note that the near-plane-wave expressions
for the form factors, when further expanded in small momentum or, equivalently,
large charge density, reproduce the thermodynamic limit of the spin-chain
results at leading order.Comment: 30 pages, 12 figures, v3: typos fixed, improved discussion of bound
states and bound state axio

### Local density of states of 1D Mott insulators and CDW states with a boundary

We determine the local density of states (LDOS) of one-dimensional
incommensurate charge density wave (CDW) states in the presence of a strong
impurity potential, which is modeled by a boundary. We find that the CDW gets
pinned at the impurity, which results in a singularity in the Fourier transform
of the LDOS at momentum 2k_F. At energies above the spin gap we observe
dispersing features associated with the spin and charge degrees of freedom
respectively. In the presence of an impurity magnetic field we observe the
formation of a bound state localized at the impurity. All of our results carry
over to the case of one dimensional Mott insulators by exchanging the roles of
spin and charge degrees of freedom. We discuss the implications of our result
for scanning tunneling microscopy experiments on spin-gap systems such as
two-leg ladder cuprates and 1D Mott insulators

### Renormalization Group Study of Magnetic Catalysis in the 3d Gross-Neveu Model

Magnetic catalysis describes the enhancement of symmetry breaking quantum
fluctuations in chirally symmetric quantum field theories by the coupling of
fermionic degrees of freedom to a magnetic background configuration. We use the
functional renormalization group to investigate this phenomenon for interacting
Dirac fermions propagating in (2+1)-dimensional spacetime, described by the
Gross-Neveu model. We identify pointlike operators up to quartic fermionic
terms that can be generated in the renormalization group flow by the presence
of an external magnetic field. We employ the beta function for the fermionic
coupling to quantitatively analyze the field dependence of the induced spectral
gap. Within our pointlike truncation, the renormalization group flow provides a
simple picture for magnetic catalysis.Comment: 14 pages, 6 figures, typos correcte

### Topological insulating phases in mono and bilayer graphene

We analyze the influence of different quadratic interactions giving rise to
time reversal invariant topological insulating phases in mono and bilayer
graphene. We make use of the effective action formalism to determine the
dependence of the Chern Simons coefficient on the different interactions

### Incidence of the boundary shape in the effective theory of fractional quantum Hall edges

Starting from a microscopic description of a system of strongly interacting
electrons in a strong magnetic field in a finite geometry, we construct the
boundary low energy effective theory for a fractional quantum Hall droplet
taking into account the effects of a smooth edge. The effective theory obtained
is the standard chiral boson theory (chiral Luttinger theory) with an
additional self-interacting term which is induced by the boundary. As an
example of the consequences of this model, we show that such modification leads
to a non-universal reduction in the tunnelling exponent which is independent of
the filling fraction. This is in qualitative agreement with experiments, that
systematically found exponents smaller than those predicted by the ordinary
chiral Luttinger liquid theory.Comment: 12 pages, minor changes, replaced by published versio

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