444 research outputs found
Antiferromagnetic spherical spin-glass model
We study the thermodynamic properties and the phase diagrams of a multi-spin
antiferromagnetic spherical spin-glass model using the replica method. It is a
two-sublattice version of the ferromagnetic spherical p-spin glass model. We
consider both the replica-symmetric and the one-step replica-symmetry-breaking
solutions, the latter being the most general solution for this model. We find
paramagnetic, spin-glass, antiferromagnetic and mixed or glassy
antiferromagnetic phases. The phase transitions are always of second order in
the thermodynamic sense, but the spin-glass order parameter may undergo a
discontinuous change.Comment: 12 pages, 6 figure
Specific heat amplitude ratios for anisotropic Lifshitz critical behaviors
We determine the specific heat amplitude ratio near a -axial Lifshitz
point and show its universal character. Using a recent renormalization group
picture along with new field-theoretical -expansion techniques,
we established this amplitude ratio at one-loop order. We estimate the
numerical value of this amplitude ratio for and . The result is in
very good agreement with its experimental measurement on the magnetic material
. It is shown that in the limit it trivially reduces to the
Ising-like amplitude ratio.Comment: 8 pages, RevTex, accepted as a Brief Report in Physical Review
An Upsilon Point in a Spin Model
We present analytic evidence for the occurrence of an upsilon point, an
infinite checkerboard structure of modulated phases, in the ground state of a
spin model. The structure of the upsilon point is studied by calculating
interface--interface interactions using an expansion in inverse spin
anisotropy.Comment: 18 pages ReVTeX file, including 6 figures encoded with uufile
A new picture of the Lifshitz critical behavior
New field theoretic renormalization group methods are developed to describe
in a unified fashion the critical exponents of an m-fold Lifshitz point at the
two-loop order in the anisotropic (m not equal to d) and isotropic (m=d close
to 8) situations. The general theory is illustrated for the N-vector phi^4
model describing a d-dimensional system. A new regularization and
renormalization procedure is presented for both types of Lifshitz behavior. The
anisotropic cases are formulated with two independent renormalization group
transformations. The description of the isotropic behavior requires only one
type of renormalization group transformation. We point out the conceptual
advantages implicit in this picture and show how this framework is related to
other previous renormalization group treatments for the Lifshitz problem. The
Feynman diagrams of arbitrary loop-order can be performed analytically provided
these integrals are considered to be homogeneous functions of the external
momenta scales. The anisotropic universality class (N,d,m) reduces easily to
the Ising-like (N,d) when m=0. We show that the isotropic universality class
(N,m) when m is close to 8 cannot be obtained from the anisotropic one in the
limit d --> m near 8. The exponents for the uniaxial case d=3, N=m=1 are in
good agreement with recent Monte Carlo simulations for the ANNNI model.Comment: 48 pages, no figures, two typos fixe
On Quantum Markov Chains on Cayley tree II: Phase transitions for the associated chain with XY-model on the Cayley tree of order three
In the present paper we study forward Quantum Markov Chains (QMC) defined on
a Cayley tree. Using the tree structure of graphs, we give a construction of
quantum Markov chains on a Cayley tree. By means of such constructions we prove
the existence of a phase transition for the XY-model on a Cayley tree of order
three in QMC scheme. By the phase transition we mean the existence of two now
quasi equivalent QMC for the given family of interaction operators
.Comment: 34 pages, 1 figur
Exact correlation functions of Bethe lattice spin models in external fields
We develop a transfer matrix method to compute exactly the spin-spin
correlation functions of Bethe lattice spin models in the external magnetic
field h and for any temperature T. We first compute the correlation function
for the most general spin - S Ising model, which contains all possible
single-ion and nearest-neighbor pair interactions. This general spin - S Ising
model includes the spin-1/2 simple Ising model and the Blume-Emery-Griffiths
(BEG) model as special cases. From the spin-spin correlation functions, we
obtain functions of correlation length for the simple Ising model and BEG
model, which show interesting scaling and divergent behavior as T approaches
the critical temperature. Our method to compute exact spin-spin correlation
functions may be applied to other Ising-type models on Bethe and Bethe-like
lattices.Comment: 19 page
Test of exotic scalar and tensor interactions in K_e3 decay using stopped positive kaons
The form factors of the decay K+ --> pi0 e+ nu (K_e3) have been determined
from the comparison of the experimental and Monte Carlo Dalitz distributions
containing about 10^5 K_e3 events. The following values of the parameters were
obtained: lambda_+ = 0.0278 +- 0.0017(stat) +- 0.0015(syst), f_S/f_+(0) =
0.0040 +- 0.0160(stat) +- 0.0067(syst) and f_T/f_+(0) = 0.019 +- 0.080(stat) +-
0.038(syst). Both scalar f_S and tensor f_T form factors are consistent with
the Standard Model predictions of zero values.Comment: 10 pages, 5 figures, contributed to the proceedings of NANP
Conference, Dubna, June 19-23, 200
A new limit of T-violating transverse muon polarization in the decay
A search for T-violating transverse muon polarization () in the
decay was performed using kaon decays at rest. A
new improved value, , was
obtained giving an upper limit, . The T-violation parameter
was determined to be Im giving
an upper limit, Im.Comment: 5 pages, 4 figure
D-branes in Generalized Geometry and Dirac-Born-Infeld Action
The purpose of this paper is to formulate the Dirac-Born-Infeld (DBI) action
in a framework of generalized geometry and clarify its symmetry. A D-brane is
defined as a Dirac structure where scalar fields and gauge field are treated on
an equal footing in a static gauge. We derive generalized Lie derivatives
corresponding to the diffeomorphism and B-field gauge transformations and show
that the DBI action is invariant under non-linearly realized symmetries for all
types of diffeomorphisms and B-field gauge transformations. Consequently, we
can interpret not only the scalar field but also the gauge field on the D-brane
as the generalized Nambu-Goldstone boson.Comment: 32 pages, 4 figures, ver2:typos corrected, references adde
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