8,379 research outputs found
Factorization of the finite temperature correlation functions of the XXZ chain in a magnetic field
We present a conjecture for the density matrix of a finite segment of the XXZ
chain coupled to a heat bath and to a constant longitudinal magnetic field. It
states that the inhomogeneous density matrix, conceived as a map which
associates with every local operator its thermal expectation value, can be
written as the trace of the exponential of an operator constructed from
weighted traces of the elements of certain monodromy matrices related to and only two transcendental functions pertaining to
the one-point function and the neighbour correlators, respectively. Our
conjecture implies that all static correlation functions of the XXZ chain are
polynomials in these two functions and their derivatives with coefficients of
purely algebraic origin.Comment: 35 page
Short-distance thermal correlations in the XXZ chain
Recent studies have revealed much of the mathematical structure of the static
correlation functions of the XXZ chain. Here we use the results of those
studies in order to work out explicit examples of short-distance correlation
functions in the infinite chain. We compute two-point functions ranging over 2,
3 and 4 lattice sites as functions of the temperature and the magnetic field
for various anisotropies in the massless regime . It turns
out that the new formulae are numerically efficient and allow us to obtain the
correlations functions over the full parameter range with arbitrary precision.Comment: 25 pages, 5 colored figure
- Vectors for Three Dimensional Models
In this paper we apply the method of psi-vectors to three dimensional
statistical models. This method gives the correspondence between the Bazhanov
-- Baxter model and its vertex formulation. Considering psi-vectors for the
Planar model, we obtain its self-duality.Comment: 11 pages, LaTeX, no figure
Exact evaluation of density matrix elements for the Heisenberg chain
We have obtained all the density matrix elements on six lattice sites for the
spin-1/2 Heisenberg chain via the algebraic method based on the quantum
Knizhnik-Zamolodchikov equations. Several interesting correlation functions,
such as chiral correlation functions, dimer-dimer correlation functions, etc...
have been analytically evaluated. Furthermore we have calculated all the
eigenvalues of the density matrix and analyze the eigenvalue-distribution. As a
result the exact von Neumann entropy for the reduced density matrix on six
lattice sites has been obtained.Comment: 33 pages, 4 eps figures, 3 author
Finite temperature density matrix and two-point correlations in the antiferromagnetic XXZ chain
We derive finite temperature versions of integral formulae for the two-point
correlation functions in the antiferromagnetic XXZ chain. The derivation is
based on the summation of density matrix elements characterizing a finite chain
segment of length . On this occasion we also supply a proof of the basic
integral formula for the density matrix presented in an earlier publication.Comment: 35 page
signals at LEP2 energies in the Minimal Supersymmetric Standard Model
In this paper we compare and into four-fermion production
at centre-of-mass energies typical of LEP2 and somewhat larger. The theoretical
framework considered is the Minimal Supersymmetric Standard Model. The interest
in exploiting the CERN collider at values of greater than
192 GeV could come from the discovery of Supersymmetric signals during runs at
lower energy. If these indicate that a charged Higgs boson exists in the mass
range \MH\approx95-105 GeV, then a few years of running at
GeV and nominal luminosity could make the detection of such scalars feasible,
in the purely leptonic channel and, for small
\tb's, also in the semi-hadronic(leptonic) one . Charged
Higgs bosons of the above nature cannot be produced by the beam energies
approved at present for LEP2. However, if runs beyond the so-called `192 GeV
cryogenic limit' will be approved by the CERN Council, our selection procedure
will enable us to establish the presence, or otherwise, of charged Higgs bosons
in the mentioned mass rangeComment: 30 pages, latex, epsfig, 12 postscript figures, complete paper
available at ftp://axpa.hep.phy.cam.ac.uk/stefano/cavendish_9615 and at
http://www.hep.phy.cam.ac.uk/theory/papers
Polarization asymmetry and the Higgs boson production mechanisms
We calculate the cross section of Higgs boson production in the reaction e+e-
-> neutrino anti-neutrino b b-bar for the case of left and right longitudinally
polarized electron beam. Complete set of signal and irreducible background
diagrams is considered.
We propose a new critical test to identify the Higgs boson provided by the
ratio of cross sections with left and right beam polarization. This quantity is
sensitive to the ratio of Higgs-W and Higgs-Z couplings, since it exhibits the
interplay of bremsstrahlung and fusion mechanisms of Higgs boson production
inherent to the Standard Model scheme.Comment: 17 pages, 6 Postscript figures, LaTeX, uses epsf.te
Mass Predictions for Pseudoscalar Charmonium and Bottomonium Hybrids in QCD Sum-Rules
Masses of the pseudoscalar charmonium and bottomonium
hybrids are determined using QCD Laplace sum-rules. The effects of the
dimension-six gluon condensate are included in our analysis and result in a
stable sum-rule analysis, whereas previous studies of these states were unable
to optimize mass predictions. The pseudoscalar charmonium hybrid is predicted
to have a mass of approximately 3.8 GeV and the corresponding bottomonium
prediction is 10.6 GeV. Calculating the full correlation function, rather than
only the imaginary part, is shown to be necessary for accurate formulation of
the sum-rules. The charmonium hybrid mass prediction is discussed within the
context of the X Y Z resonances.Comment: 10 pages, 7 embedded figures. Analysis extended and refined in v
Double fermiophobic Higgs boson production at the LHC and LC
We consider the phenomenology of a fermiophobic Higgs boson (h_f) at the
Large Hadron Collider (LHC) and a e+e- Linear Collider (LC). At both machines
the standard production mechanisms which rely on the coupling h_fVV (V=W,Z) can
be very suppressed at large tan beta. In such cases the complementary channels
pp to H^\pm h_f, A^0 h_f and e+e- to A^0 h_f offer promising cross-sections.
Together with the potentially large branching ratios for H^\pm to h_fW* and A^0
to h_fZ*, these mechanisms would give rise to double h_f production, leading to
signatures of gamma gamma gamma gamma, gamma gamma VV and VVVV.Comment: 19 pages, 9 figures, expanded discussion, fig.1 changed slightly,
version to appear in Phys.Rev.
Traces on the Sklyanin algebra and correlation functions of the eight-vertex model
We propose a conjectural formula for correlation functions of the Z-invariant
(inhomogeneous) eight-vertex model. We refer to this conjecture as Ansatz. It
states that correlation functions are linear combinations of products of three
transcendental functions, with theta functions and derivatives as coefficients.
The transcendental functions are essentially logarithmic derivatives of the
partition function per site. The coefficients are given in terms of a linear
functional on the Sklyanin algebra, which interpolates the usual trace on
finite dimensional representations. We establish the existence of the
functional and discuss the connection to the geometry of the classical limit.
We also conjecture that the Ansatz satisfies the reduced qKZ equation. As a
non-trivial example of the Ansatz, we present a new formula for the
next-nearest neighbor correlation functions.Comment: 35 pages, 2 figures, final versio
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