9,055 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
Fermionic screening operators in the sine-Gordon model
Extending our previous construction in the sine-Gordon model, we show how to
introduce two kinds of fermionic screening operators, in close analogy with
conformal field theory with c<1.Comment: 18 pages, 1 figur
Minimal Gauge Invariant Classes of Tree Diagrams in Gauge Theories
We describe the explicit construction of groves, the smallest gauge invariant
classes of tree Feynman diagrams in gauge theories. The construction is valid
for gauge theories with any number of group factors which may be mixed. It
requires no summation over a complete gauge group multiplet of external matter
fields. The method is therefore suitable for defining gauge invariant classes
of Feynman diagrams for processes with many observed final state particles in
the standard model and its extensions.Comment: 13 pages, RevTeX (EPS figures
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
Fifth-neighbor spin-spin correlator for the anti-ferromagnetic Heisenberg chain
We study the generating function of the spin-spin correlation functions in
the ground state of the anti-ferromagnetic spin-1/2 Heisenberg chain without
magnetic field. We have found its fundamental functional relations from those
for general correlation functions, which originate in the quantum
Knizhink-Zamolodchikov equation. Using these relations, we have calculated the
explicit form of the generating functions up to n=6. Accordingly we could
obtain the spin-spin correlator up to k=5.Comment: 10 page
CompHEP 4.4 - Automatic Computations from Lagrangians to Events
We present a new version of the CompHEP program (version 4.4). We describe
shortly new issues implemented in this version, namely, simplification of quark
flavor combinatorics for the evaluation of hadronic processes, Les Houches
Accord based CompHEP-PYTHIA interface, processing the color configurations of
events, implementation of MSSM, symbolical and numerical batch modes, etc. We
discuss how the CompHEP program is used for preparing event generators for
various physical processes. We mention a few concrete physics examples for
CompHEP based generators prepared for the LHC and Tevatron.Comment: The paper has been presented on IX International Workshop on Advanced
Computing and Analysis Techniques in Physics Research December 1-5, 2003.
KEK, Japan. 10 pages, 2 figure
Asymptotic Behavior of the Emptiness Formation Probability in the Critical Phase of XXZ Spin Chain
We study the Emptiness Formation Probability (EFP) for the spin 1/2 XXZ spin
chain. EFP P(n) detects a formation of ferromagnetic string of the length n in
the ground state. It is expected that EFP decays in a Gaussian way for large
strings P(n) ~ n^{-gamma} C^{-n^2}. Here, we propose the explicit expressions
for the rate of Gaussian decay C as well as for the exponent gamma. In order to
confirm the validity of our formulas, we employed an ab initio simulation
technique of the density-matrix renormalization group to simulate XXZ spin
chain of sufficient length. Furthermore, we performed Monte-Carlo integration
of the Jimbo-Miwa multiple integral for P(n). Those numerical results for P(n)
support our formulas fairly definitely.Comment: 9 pages, 2 figure
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