1,514 research outputs found
Electromagnetic response and effective gauge theory of graphene in a magnetic field
The electromagnetic response of graphene in a magnetic field is studied, with
particular emphasis on the quantum features of its ground state (vacuum). The
graphene vacuum, unlike in conventional quantum Hall systems, is a dielectric
medium and carries an appreciable amount of electric and magnetic
susceptibilities. The dielectric effect grows rapidly with increasing filling
factor nu in such a way that reflects the 'relativistic' Landau-level
characteristics of graphene as well as its valley and spin degeneracy. A close
look into the dielectric function also reveals that the Coulomb interaction is
efficiently screened on the scale of the magnetic length, leading to a
prominent reduction of the exciton spectra in graphene. In addition, an
effective gauge theory of graphene is constructed out of the response. It is
pointed out thereby that the electric susceptibility is generally expressed as
a ratio of the Hall conductance to the Landau gap.Comment: 9 pages, 3 figures, revtex, corrected typo
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
Holst Actions for Supergravity Theories
Holst action containing Immirzi parameter for pure gravity is generalised to
the supergravity theories. Supergravity equations of motion are not modified by
such generalisations, thus preserving supersymmetry. Dependence on the Immirzi
parameter does not emerge in the classical equations of motion. This is in
contrast with the recent observation of Perez and Rovelli for gravity action
containing original Holst term and a minimally coupled Dirac fermion where the
classical equations of motion do develop a dependence on Immirzi parameter.Comment: 15 page
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
One-particle and collective electron spectra in hot and dense QED and their gauge dependence
The one-particle electron spectrum is found for hot and dense QED and its
properties are investigated in comparison with the collective spectrum. It is
shown that the one-particle spectrum (in any case its zero momentum limit) is
gauge invariant, but the collective spectrum, being qualitatively different, is
always gauge dependent. The exception is the case for which the
collective spectrum long wavelength limit demonstrates the gauge invariance as
well.Comment: 9 pages, latex, no figure
Spin solid phases of spin 1 and spin 3/2 antiferromagnets on a cubic lattice
We study spin S=1 and S=3/2 Heisenberg antiferromagnets on a cubic lattice
focusing on spin solid states. Using Schwinger boson formulation for spins, we
start in a U(1) spin liquid phase proximate to Neel phase and explore possible
confining paramagnetic phases as we transition away from the spin liquid by the
process of monopole condensation. Electromagnetic duality is used to rewrite
the theory in terms of monopoles. For spin 1 we find several candidate phases
of which the most natural one is a phase with spins organized into parallel
Haldane chains. For spin 3/2 we find that the most natural phase has spins
organized into parallel ladders. As a by-product, we also write a Landau theory
of the ordering in two special classical frustrated XY models on the cubic
lattice, one of which is the fully frustrated XY model. In a particular limit
our approach maps to a dimer model with 2S dimers coming out of every site, and
we find the same spin solid phases in this regime as well.Comment: 15 pages, 8 figure
Background Free Quantum Gravity based on Conformal Gravity and Conformal Field Theory on M^4
We study four dimensional quantum gravity formulated as a certain conformal
field theory at the ultraviolet fixed point, whose dynamics is described by the
combined system of Riegert-Wess-Zumino and Weyl actions. Background free nature
comes out as quantum diffeomorphism symmetry by quantizing the conformal factor
of the metric field nonperturbatively. In this paper, Minkowski background M^4
is employed in practice. The generator of quantum diffeomorphism that forms
conformal algebra is constructed. Using it, we study the composite scalar
operator that becomes a good conformal field. We find that physical fields are
described by such scalar fields with conformal dimension 4. Consequently,
tensor fields outside the unitarity bound are excluded. Computations of quantum
algebra on M^4 are carried out in the coordinate space using operator products
of the fields. The nilpotent BRST operator is also constructed.Comment: 43 pages, eqs.(3.9) and (6.18) correcte
The wall of the cave
In this article old and new relations between gauge fields and strings are
discussed. We add new arguments that the Yang Mills theories must be described
by the non-critical strings in the five dimensional curved space. The physical
meaning of the fifth dimension is that of the renormalization scale represented
by the Liouville field. We analyze the meaning of the zigzag symmetry and show
that it is likely to be present if there is a minimal supersymmetry on the
world sheet. We also present the new string backgrounds which may be relevant
for the description of the ordinary bosonic Yang-Mills theories. The article is
written on the occasion of the 40-th anniversary of the IHES.Comment: 18 pages, Late
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