30,902 research outputs found
TFD Approach to Bosonic Strings and -branes
In this work we explain the construction of the thermal vacuum for the
bosonic string, as well that of the thermal boundary state interpreted as a
-brane at finite temperature. In both case we calculate the respective
entropy using the entropy operator of the Thermo Field Dynamics Theory. We show
that the contribution of the thermal string entropy is explicitly present in
the -brane entropy. Furthermore, we show that the Thermo Field approach
is suitable to introduce temperature in boundary states.Comment: 6 pages, revtex, typos are corrected. Prepared for the Second
Londrina Winter School-Mathematical Methods in Physics, August 25-30, 2002,
Londrina-Pr, Brazil. To appear in a special issue of IJMP
Impact of the Neutrino Magnetic Moment on the Neutrino Fluxes and the Electron Fraction in core-collapse Supernovae
We explore the effect of the neutrino magnetic moment on neutrino scattering
with matter in a core-collapse Supernova. We study the impact both on the
neutrino fluxes and on the electron fraction. We find that sizeable
modifications require very large magnetic moments both for Dirac and Majorana
neutrinos.Comment: 7 pages, 6 figure
The Toulose limit of the Multi-Channel Kondo model.
We study the Toulouse limit of the multi-channel Kondo model defined as the
limit of maximal anisotropy which can be achieved without changing the infrared
behaviour of the model. It is shown that when the number of channels exceeds 2,
the interactions do not vanish and the Toulouse limit remains a non-trivial
field theory. Considerable simplifications take place only for k = 2, where the
Bethe ansatz reproduces the results by Emery and Kivelson.Comment: 10 pages, LaTex, a discussion about the magnetic properties is added
Quantum Spin Chains and Riemann Zeta Function with Odd Arguments
Riemann zeta function is an important object of number theory. It was also
used for description of disordered systems in statistical mechanics. We show
that Riemann zeta function is also useful for the description of integrable
model. We study XXX Heisenberg spin 1/2 anti-ferromagnet. We evaluate a
probability of formation of a ferromagnetic string in the anti-ferromagnetic
ground state in thermodynamics limit. We prove that for short strings the
probability can be expressed in terms of Riemann zeta function with odd
arguments.Comment: LaTeX, 7 page
Spin-Wave Theory of the Spiral Phase of the t-J Model
A graded H.P,realization of the SU(2|1) algebra is proposed.A spin-wave
theory with a condition that the sublattice magnetization is zero is
discussed.The long-range spiral phase is investigated.The spin-spin correlator
is calculated.Comment: 17 page
Spin Waves in Random Spin Chains
We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute, random
antiferromagnetic impurity bonds with modified spin-wave theory. By describing
thermal excitations in the language of spin waves, we successfully observe a
low-temperature Curie susceptibility due to formation of large spin clusters
first predicted by the real-space renormalization-group approach, as well as a
crossover to a pure ferromagnetic spin chain behavior at intermediate and high
temperatures. We compare our results of the modified spin-wave theory to
quantum Monte Carlo simulations.Comment: 3 pages, 3 eps figures, submitted to the 47th Conference on Magnetism
and Magnetic Material
A rotating cavity for high-field angle-dependent microwave spectroscopy of low-dimensional conductors and magnets
The cavity perturbation technique is an extremely powerful method for
measuring the electrodynamic response of a material in the millimeter- and
sub-millimeter spectral range (10 GHz to 1 THz), particularly in the case of
high-field/frequency magnetic resonance spectroscopy. However, the application
of such techniques within the limited space of a high-field magnet presents
significant technical challenges. We describe a 7.62 mm x 7.62 mm (diameter x
length) rotating cylindrical cavity which overcomes these problems.Comment: 11 pages including 8 figure
Nonlinear Integral Equations for Thermodynamics of the U_{q}(\hat{sl(r+1)}) Perk-Schultz Model
We propose a system of nonlinear integral equations (NLIE) which describes
the thermodynamics of the U_{q}(\hat{sl(r+1)}) Perk-Schultz model. These NLIE
correspond to a trigonometric analogue of our previous result
(cond-mat/0212280), and contain only r unknown functions. In particular, they
reduce to Takahashi's NLIE for the XXZ spin chain (cond-mat/0010486) if r=1. We
also calculate the high temperature expansion of the free energy. In particular
for r=1 case, we have succeeded to derive the coefficients of order
O((\frac{J}{T})^{99}).Comment: 19 pages, 4 figures, only the Mathematica file for the high
temperature expansion is replaced, to appear in J.Phys.Soc.Jpn.Vol.74 No.3
(2005
The baryonic Y-shape confining potential energy and its approximants
We discuss the validity of replacing the complicated three-body confinement
operator of the Y string junction type by three kinds of approximation which
are numerically much simpler to handle: a one-body operator with the junction
point at the centre of mass, a two-body operator corresponding to half the
perimeter of the triangle formed by the three particles, and the average of
both. Two different approaches for testing the quality of the approximations
are proposed: a geometrical treatment based on the comparison of the potential
energy strengths for the various inter quark distances, and a dynamical
treatment based on the comparison of the corresponding effective string
tensions using a hyperspherical approach. Both procedures give very similar
results. It is shown how to simulate the genuine string junction operator by
the approximations proposed above. Exact three-body calculations are presented
in order to compare quantitatively the various approximations and to confirm
our analysis.Comment: 28 pages, 5 figures, submitted to EPJ
Finite-Temperature Scaling of Magnetic Susceptibility and Geometric Phase in the XY Spin Chain
We study the magnetic susceptibility of 1D quantum XY model, and show that
when the temperature approaches zero, the magnetic susceptibility exhibits the
finite-temperature scaling behavior. This scaling behavior of the magnetic
susceptibility in 1D quantum XY model, due to the quantum-classical mapping,
can be easily experimentally tested. Furthermore, the universality in the
critical properties of the magnetic susceptibility in quantum XY model is
verified. Our study also reveals the close relation between the magnetic
susceptibility and the geometric phase in some spin systems, where the quantum
phase transitions are driven by an external magnetic field.Comment: 6 pages, 4 figures, get accepted for publication by J. Phys. A: Math.
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