1,459 research outputs found
Equation of state for the 2+1 dimensional Gross-Neveu model at order 1/N
We calculate the equation of state of the Gross-Neveu model in 2+1 dimensions
at order 1/N, where N is the number of fermion species. We make use of a
general formula valid for four-fermion theories, previously applied to the
model in 1+1 dimensions. We consider both the discrete and continuous symmetry
versions of the model. We show that the pion-like excitations give the dominant
contribution at low temperatures. The range of validity for such pion dominance
is analyzed. The complete analysis from low to high temperatures also shows
that in the critical region the role of composite states is relevant, even for
quite large N, and that the free-component behaviour at high T starts at about
twice the mean field critical temperature.Comment: 19 pages, RevTeX, 10 figures.p
Nature of 45 degree vortex lattice reorientation in tetragonal superconductors
The transformation of the vortex lattice in a tetragonal superconductor which
consists of its 45 degree reorientation relative to the crystal axes is studied
using the nonlocal London model. It is shown that the reorientation occurs as
two successive second order (continuous) phase transitions. The transition
magnetic fields are calculated for a range of parameters relevant for
borocarbide superconductors in which the reorientation has been observed
Effects in Chern-Simons with a Four-Fermi Interaction
We investigate the effects of the Chern-Simons coupling on the high energy
behavior in the -dimensional Chern-Simons QED with a four-Fermi
interaction. Using the expansion we discuss the Chern-Simons effects on
the critical four-Fermi coupling at and the function around
it. High-energy behavior of Green's functions is also discussed. By explicit
calculation, we find that the radiative correction to the Chern-Simons coupling
vanishes at in the broken phase of the dynamical parity symmetry. We
argue that no radiative corrections to the Chern-Simons term arise at higher
orders in the expansion.Comment: 13 pages, 6 figures not included, LaTeX, SNUTP 92-9
The Dynamical Behaviors in (2+1)-Dimensional Gross-Neveu Model with a Thirring Interaction
We analyze (2+1)-dimensional Gross-Neveu model with a Thirring interaction,
where a vector-vector type four-fermi interaction is on equal terms with a
scalar-scalar type one. The Dyson-Schwinger equation for fermion self-energy
function is constructed up to next-to-leading order in 1/N expansion. We
determine the critical surface which is the boundary between a broken phase and
an unbroken one in () space. It is observed that the
critical behavior is mainly controlled by Gross-Neveu coupling and
the region of the broken phase is separated into two parts by the line
. The mass function is strongly
dependent upon the flavor number N for , while weakly for
, the critical flavor number
increases as Thirring coupling decreases. By driving the CJT
effective potential, we show that the broken phase is energetically preferred
to the symmetric one. We discuss the gauge dependence of the mass function and
the ultra-violet property of the composite operators.Comment: 19 pages, LaTex, 6 ps figure files(uuencoded in seperate file
Thermal fluctuations and disorder effects in vortex lattices
We calculate using loop expansion the effect of fluctuations on the structure
function and magnetization of the vortex lattice and compare it with existing
MC results. In addition to renormalization of the height of the Bragg peaks of
the structure function, there appears a characteristic saddle shape ''halos''
around the peaks. The effect of disorder on magnetization is also calculated.
All the infrared divergencies related to soft shear cancel.Comment: 10 pages, revtex file, one figur
Current Algebra in Three Dimensions
We study a three dimensional analogue of the Wess--Zumino--Witten model,
which describes the Goldstone bosons of three dimensional Quantum
Chromodynamics. The topologically non--trivial term of the action can also be
viewed as a nonlinear realization of Chern--Simons form. We obtain the current
algebra of this model by canonical methods. This is a three dimensional
generalization of the Kac--Moody algebra.Comment: 11 pages, UR-1266, ER40685-72
Dynamical Symmetry Breaking in Models with the Yukawa Interaction
We discuss models with a massless fermion and a self-interacting massive
scalar field with the Yukawa interaction. The chiral condensate and the fermion
mass are calculated analytically. It is shown that the models have a phase
transition as a function of the squared mass of the scalar field.Comment: 7 pages, no figures, in Eqs. (7) and (11) one coefficient was change
Why the lowest Landau level approximation works in strongly type II superconductors
Higher than the lowest Landau level contributions to magnetization and
specific heat of superconductors are calculated using Ginzburg - Landau
equations approach. Corrections to the excitation spectrum around solution of
these equations (treated perturbatively) are found. Due to symmetries of the
problem leading to numerous cancellations the range of validity of the LLL
approximation in mean field is much wider then a naive range and extends all
the way down to . Moreover the contribution of higher
Landau levels is significantly smaller compared to LLL than expected naively.
We show that like the LLL part the lattice excitation spectrum at small
quasimomenta is softer than that of usual acoustic phonons. This enhanses the
effect of fluctuations. The mean field calculation extends to third order,
while the fluctuation contribution due to HLL is to one loop. This complements
the earlier calculation of the LLL part to two loop order.Comment: 20 pages, Latex file, three figure
O(1/N_f) Corrections to the Thirring Model in 2<d<4
The Thirring model, that is, a relativistic field theory of fermions with a
contact interaction between vector currents, is studied for dimensionalities
2<d<4 using the 1/N_f expansion, where N_f is the number of fermion species.
The model is found to have no ultraviolet divergences at leading order provided
a regularization respecting current conservation is used. Explicit O(1/N_f)
corrections are computed, and the model shown to be renormalizable at this
order in the massless limit; renormalizability appears to hold to all orders
due to a special case of Weinberg's theorem. This implies there is a universal
amplitude for four particle scattering in the asymptotic regime. Comparisons
are made with both the Gross-Neveu model and QED.Comment: 22 pages in plain TeX, with 7 figs included using psfig.tex (Minor
conceptual changes - algebra unaffected
Classicalization and Unitarity
We point out that the scenario for UV completion by "classicalization",
proposed recently is in fact Wilsonian in the classical Wilsonian sense. It
corresponds to the situation when a field theory has a nontrivial UV fixed
point governed by a higher dimensional operator. Provided the kinetic term is a
relevant operator around this point the theory will flow in the IR to the free
scalar theory. Physically, "classicalization", if it can be realized, would
correspond to a situation when the fluctuations of the field operator in the UV
are smaller than in the IR. As a result there exists a clear tension between
the "classicalization" scenario and constraints imposed by unitarity on a
quantum field theory, making the existence of classicalizing unitary theories
questionable.Comment: Some clarifications and refs added. Accepted as a JHEP publication;
12 page
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