1,347 research outputs found
Time-Reversal Symmetry Breaking and Spontaneous Anomalous Hall Effect in Fermi Fluids
We study the spontaneous non-magnetic time-reversal symmetry breaking in a
two-dimensional Fermi liquid without breaking either the translation symmetry
or the U(1) charge symmetry. Assuming that the low-energy physics is described
by fermionic quasiparticle excitations, we identified an "emergent" local
symmetry in momentum space for an -band model. For a large class of
models, including all one-band and two-band models, we found that the
time-reversal and chiral symmetry breaking can be described by the
gauge theory associated with this emergent local symmetry. This
conclusion enables the classification of the time-reversal symmetry-breaking
states as types I and II, depending on the type of accompanying spatial
symmetry breaking. The properties of each class are studied. In particular, we
show that the states breaking both time-reversal and chiral symmetries are
described by spontaneously generated Berry phases. We also show examples of the
time-reversal symmetry-breaking phases in several different microscopically
motivated models and calculate their associated Hall conductance within a
mean-field approximation. The fermionic nematic phase with time-reversal
symmetry breaking is also presented and the possible realizations in strongly
correlated models such as the Emery model are discussed.Comment: 18 pages, 8 figure
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
Interactions and the Theta Term in One-Dimensional Gapped Systems
We study how the \theta -term is affected by interactions in certain
one-dimensional gapped systems that preserve charge-conjugation, parity, and
time-reversal invariance. We exploit the relation between the chiral anomaly of
a fermionic system and the classical shift symmetry of its bosonized dual. The
vacuum expectation value of the dual boson is identified with the value of the
\theta -term for the corresponding fermionic system. Two (related) examples
illustrate the identification. We first consider the massive Luttinger liquid
and find the \theta -term to be insensitive to the strength of the interaction.
Next, we study the continuum limit of the Heisenberg XXZ spin-1/2 chain,
perturbed by a second nearest-neighbor spin interaction. For a certain range of
the XXZ anisotropy, we find that we can tune between two distinct sets of
topological phases by varying the second nearest-neighbor coupling. In the
first, we find the standard vacua at \theta = 0, \pi, while the second contains
vacua that spontaneously break charge-conjugation and parity with fractional
\theta / \pi = 1/ 2, 3/2. We also study quantized pumping in both examples
following recent work.Comment: 17 pages, harvmac; v.2 typo corrected and slight re-wording
External leg amputation in conformal invariant three-point function
Amputation of external legs is carried out explicitly for the conformal
invariant three-point function involving two spinors and one vector field. Our
results are consistent with the general result that amputing an external leg in
a conformal invariant Green function replaces a field by its conformal partner
in the Green function. A new star-triangle relation, involving two spinors and
one vector field, is derived and used for the calculation.Comment: 16 pages; last paragraph added in Sec. 10, presentation improved, to
appear in Eur. Phys. J.
Three-point Green function of massless QED in position space to lowest order
The transverse part of the three-point Green function of massless QED is
determined to the lowest order in position space. Taken together with the
evaluation of the longitudinal part in arXiv:0803.2630, this gives a relation
for QED which is analogous to the star-triangle relation. We relate our result
to conformal-invariant three-point functions.Comment: 8 page
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
One-loop counterterms for the dimensional regularization of arbitrary Lagrangians
We present master formulas for the divergent part of the one-loop effective
action for an arbitrary (both minimal and nonminimal) operators of any order in
the 4-dimensional curved space. They can be considered as computer algorithms,
because the one-loop calculations are then reduced to the simplest algebraic
operations. Some test applications are considered by REDUCE analytical
calculation system.Comment: 39 pages, Latex, 3 PS figures, replaced with published versio
On the pathwidth of almost semicomplete digraphs
We call a digraph {\em -semicomplete} if each vertex of the digraph has at
most non-neighbors, where a non-neighbor of a vertex is a vertex such that there is no edge between and in either direction.
This notion generalizes that of semicomplete digraphs which are
-semicomplete and tournaments which are semicomplete and have no
anti-parallel pairs of edges. Our results in this paper are as follows. (1) We
give an algorithm which, given an -semicomplete digraph on vertices
and a positive integer , in time either
constructs a path-decomposition of of width at most or concludes
correctly that the pathwidth of is larger than . (2) We show that there
is a function such that every -semicomplete digraph of pathwidth
at least has a semicomplete subgraph of pathwidth at least .
One consequence of these results is that the problem of deciding if a fixed
digraph is topologically contained in a given -semicomplete digraph
admits a polynomial-time algorithm for fixed .Comment: 33pages, a shorter version to appear in ESA 201
Quantum Metamorphosis of Conformal Transformation in D3-Brane Yang-Mills Theory
We show how the linear special conformal transformation in four-dimensional
N=4 super Yang-Mills theory is metamorphosed into the nonlinear and
field-dependent transformation for the collective coordinates of Dirichlet
3-branes, which agrees with the transformation law for the space-time
coordinates in the anti-de Sitter (AdS) space-time. Our result provides a new
and strong support for the conjectured relation between AdS supergravity and
super conformal Yang-Mills theory (SYM). Furthermore, our work sheds
elucidating light on the nature of the AdS/SYM correspondence.Comment: 8 pages, no figure
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