1,761 research outputs found
The anisotropic Heisenberg model in a transverse magnetic field
One dimensional spin-1/2 model in a transverse magnetic field is
studied. It is shown that the field induces the gap in the spectrum of the
model with easy-plain anisotropy. Using conformal invariance the field
dependence of the gap at small fields is found. The ground state phase diagram
is obtained. It contains four phases with different types of the long range
order (LRO) and a disordered one. These phases are separated by critical lines,
where the gap and the long range order vanish. Using scaling estimations and a
mean-field approach as well as numerical calculations in the vicinity of all
critical lines we found the critical exponents of the gap and the LRO. It is
shown that transition line between the ordered and disordered phases belongs to
the universality class of the transverse Ising model.Comment: 10 pages, 3 figures, LaTe
Multiphonon anharmonic decay of a quantum mode
A nonperturbative theory of multiphonon anharmonic transitions between energy
levels of a local mode is presented. It is shown that the rate of transitions
rearranges near the critical level number : at smaller the process
slows down, while at larger it accelerates in time, causing a jump-like
loss of energy followed by the generation of phonon bursts. Depending on
parameters, phonons are emitted in pairs, triplets etc.Comment: submitted to Europhys.Let
Massive liquid Ar and Xe detectors for direct Dark Matter searches
A novel experiment for direct searches of the Dark Matter with liquid argon
double-phase chamber with a mass of liquid Ar up to several hundred tons is
proposed. To suppress the b-, g- and n0- backgrounds, the comparison of
scintillation and ionization signals for every event is suggested. The addition
in liquid Ar of photosensitive Ge(CH3)4 or C2H4 and suppression of triplet
component of scintillation signals ensures the detection of scintillation
signals with high efficiency and provides a complete suppression of the
electron background. For the detection of photoelectrons and ionization
electrons, highly stable and reliable GEM detectors must be used.Comment: 8 pages, 2 figures, 1 tabl
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