4,378 research outputs found
Semi-fermionic representation of SU(N) Hamiltonians
We represent the generators of the SU(N) algebra as bilinear combinations of
Fermi operators with imaginary chemical potential. The distribution function,
consisting of a minimal set of discrete imaginary chemical potentials, is found
for arbitrary N. This representation leads to the conventional temperature
diagram technique with standard Feynman codex, except that the Matsubara
frequencies are determined by neither integer nor half-integer numbers. The
real-time Schwinger-Keldysh formalism is formulated in the framework of complex
distribution functions. We discuss the continuous large N and SU(2) large spin
limits. We illustrate the application of this technique for magnetic and
spin-liquid states of the Heisenberg model.Comment: 11 pages, 7 EPS figures included, extended versio
Prospects for the Bc Studies at LHCb
We discuss the motivations and perspectives for the studies of the mesons of
the (bc) family at LHCb. The description of production and decays at LHC
energies is given in details. The event yields, detection efficiencies, and
background conditions for several Bc decay modes at LHCb are estimated.Comment: 20 pages, 5 eps-figure
Dromion perturbation for the Davey-Stewartson-1 equations
The perturbation of the dromion of the Davey-Stewartson-1 equation is studied
over the large time
Two-particle decays of B_c meson into charmonium states
The factorization of hard and soft contributions into the hadronic decays of
B_c meson at large recoils is explored in order to evaluate the decay rates
into the S, P and D-wave charmonia associated with rho and pi. The constraints
of approach applicability and uncertainties of numerical estimates are
discussed. The mode with the J/psi in the final state is evaluated taking into
account the cascade radiative electromagnetic decays of excited P-wave states,
that enlarges the branching ratio by 20-25%.Comment: 13 pages, LaTeX axodraw-style, 1 figure, 2 table
Gold-plated Mode of CP-Violation in Decays of B_c Meson from QCD Sum Rules
The model-independent method based on the triangle ideology is implemented to
extract the CKM-matrix angle gamma in the decays of doubly heavy long-lived
meson B_c. We analyze a color structure of diagrams and conditions to
reconstruct two reference-triangles by tagging the flavor and CP eigenstates of
D^0 meson in the fixed exclusive channels. The characteristic branching ratios
are evaluated in the framework of QCD sum rules.Comment: 11 pages, RevTeX4 file, 4 eps-figure
Quenching and Propagation of Combustion Without Ignition Temperature Cutoff
We study a reaction-diffusion equation in the cylinder , with combustion-type reaction term without
ignition temperature cutoff, and in the presence of a periodic flow. We show
that if the reaction function decays as a power of larger than three as
and the initial datum is small, then the flame is extinguished -- the
solution quenches. If, on the other hand, the power of decay is smaller than
three or initial datum is large, then quenching does not happen, and the
burning region spreads linearly in time. This extends results of
Aronson-Weinberger for the no-flow case. We also consider shear flows with
large amplitude and show that if the reaction power-law decay is larger than
three and the flow has only small plateaux (connected domains where it is
constant), then any compactly supported initial datum is quenched when the flow
amplitude is large enough (which is not true if the power is smaller than three
or in the presence of a large plateau). This extends results of
Constantin-Kiselev-Ryzhik for combustion with ignition temperature cutoff. Our
work carries over to the case , when
the critical power is , as well as to certain non-periodic flows
Semileptonic transition in three--point QCD sum rules and HQET with gluon condensate corrections
Taking into account the gluon condensate contributions, the form factors of
the semileptonic transition with are
calculated in the framework of the three point QCD sum rules. The heavy quark
effective theory limit of the form factors are also computed. The relevant
total decay width as well as the branching ratio are evaluated and compared
with the predictions of the other non-perturbative approaches.Comment: 27 Pages, 4 Figures and 4 Table
Mass spectra of doubly heavy Omega_QQ' baryons
We evaluate the masses of baryons composed of two heavy quarks and a strange
quark with account for spin-dependent splittings in the framework of potential
model with the KKO potential motivated by QCD with a three-loop beta-function
for the effective charge consistent with both the perturbative limit at short
distances and linear confinement term at long distances between the quarks. The
factorization of dynamics is supposed and explored in the nonrelativistic
Schroedinger equation for the motion in the system of two heavy quarks
constituting the doubly heavy diquark and the strange quark interaction with
the diquark. The limits of approach, its justification and uncertainties are
discussed. Excited quasistable states are classified by the quantum numbers of
heavy diquark composed by the heavy quarks of the same flavor.Comment: 14 pages, revtex4-file, 3 eps-figures, 5 tables, typos correcte
One-Loop Corrections to Bubble Nucleation Rate at Finite Temperature
We present an evaluation of the 1-loop prefactor in the lifetime of a
metastable state which decays at finite temperature by bubble nucleation. Such
a state is considered in one-component phi^4 model in three space dimensions.
The calculation serves as a prototype application of a fast numerical method
for evaluating the functional determinants that appear in semiclassical
approximations.Comment: DO-TH-93/18, 15 pages, 11 Figures available on request, LaTeX, no
macros neede
Centipede ladder at quarter filling
We study the ground state and excitation spectrum of a quasi one-dimensional
nanostructure consisting of a pole and rungs oriented in the opposite
directions ("centipede ladder", CL) at quarter filling. The spin and charge
excitation spectra are found in the limits of small and large longitudinal
hopping compared to the on-rung hopping rate and exchange
coupling . At small the system with ferromagnetic on-rung
exchange demonstrates instability against dimerization. Coherent propagation of
charge transfer excitons is possible in this limit. At large CL behaves
like two-orbital Hubbard chain, but the gap opens in the charge excitation
spectrum thus reducing the symmetry from SU(4) to SU(2). The spin excitations
are always gapless and their dispersion changes from quadratic magnon-like for
ferromagnetic on-rung exchange to linear spinon-like for antiferromagnetic
on-rung exchange in weak longitudinal hopping limit.Comment: 10 pages, 7 eps figure
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