32,015 research outputs found
Effective actions at finite temperature
This is a more detailed version of our recent paper where we proposed, from
first principles, a direct method for evaluating the exact fermion propagator
in the presence of a general background field at finite temperature. This can,
in turn, be used to determine the finite temperature effective action for the
system. As applications, we discuss the complete one loop finite temperature
effective actions for 0+1 dimensional QED as well as for the Schwinger model in
detail. These effective actions, which are derived in the real time (closed
time path) formalism, generate systematically all the Feynman amplitudes
calculated in thermal perturbation theory and also show that the retarded
(advanced) amplitudes vanish in these theories. Various other aspects of the
problem are also discussed in detail.Comment: 9 pages, revtex, 1 figure, references adde
Effective Actions for 0+1 Dimensional Scalar QED and its SUSY Generalization at
We compute the effective actions for the 0+1 dimensional scalar field
interacting with an Abelian gauge background, as well as for its supersymmetric
generalization at finite temperature.Comment: 5 pages, Latex fil
Astrophysical Implications of the Superstring-Inspired E_6 Unification and Shadow Theta-Particles
We have developed a concept of parallel existence of the ordinary (O) and
mirror (M), or shadow (Sh) worlds. E_6 unification, inspired by superstring
theory, restores the broken mirror parity at the scale ~ 10^18 GeV. With the
aim to explain the tiny cosmological constant, we consider the breakings: E_6
-> SO(10) X U(1)_Z - in the O-world, and E'_6 -> SU(6)' X SU(2)'_\theta - in
the Sh-world. We assume the existence of shadow \theta-particles and the low
energy symmetry group SU(3)'_C X SU(2)'_L X SU(2)'_\theta X U(1)'_Y in the
shadow world, instead of the Standard Model. The additional non-Abelian
SU(2)'_\theta group with massless gauge fields, "thetons", has a macroscopic
confinement radius 1/\Lambda'_\theta. The assumption that
\Lambda'_\theta\approx 2.3 X 10^-3 eV explains the tiny cosmological constant
given by recent astrophysical measurements. Searching for the Dark Matter (DM),
it is possible to observe and study various signals of theta-particles.Comment: 6 pages, 2 figures, presented at "Invisble Universe International
Conference", Palais de l'UNESCO, Paris, France, June 29 - July 3, 200
Visualizing electron pockets in cuprate superconductors
Fingerprint of the electron-pocket in cuprates has been obtained only in
numerous magneto-transport measurements, but its absence in spectroscopic
observations pose a long-standing mystery. We develop a theoretical tool to
provide ways to detect electron-pockets via numerous spectroscopies including
scanning tunneling microscopy (STM) spectra, inelastic neutron scattering
(INS), and angle-resolved photoemission spectroscopy (ARPES). We show that the
quasiparticle-interference (QPI) pattern, measured by STM, shows additional 7
vectors associated with the scattering on the electron-pocket, than
that on the hole-pocket. Furthermore, the Bogolyubov quasiparticle scatterings
of the electron pocket may lead to a second magnetic resonance mode in the INS
spectra at a higher resonance energy. Finally, we reanalyze some STM, INS, and
ARPES experimental data of several cuprate compounds which dictates the direct
fingerprints of electron pockets in these systems.Comment: 10 pages, 6 figures, submitte
Topological Structure of the Vacuum, Cosmological Constant and Dark Energy
In this review we present a theory of cosmological constant and Dark Energy
(DE), based on the topological structure of the vacuum. The Multiple Point
Principle (MPP) is reviewed. It demonstrates the existence of the two vacua
into the SM. The Froggatt-Nielsen's prediction of the top-quark and Higgs
masses is given in the assumption that there exist two degenerate vacua in the
SM. This prediction was improved by the next order calculations. We also
considered B.G. Sidharth's theory of cosmological constant based on the
non-commutative geometry of the Planck scale space-time, what gives an
extremely small DE density providing the accelerating expansion of the
Universe. Theory of two degenerate vacua - the Planck scale phase and
Electroweak (EW) phase - also is reviewed, topological defects in these vacua
are investigated, also the Compton wavelength phase suggested by B.G. Sidharth
was discussed. A general theory of the phase transition and the problem of the
vacuum stability in the SM is reviewed. Assuming that the recently discovered
at the LHC new resonance with mass GeV is a new scalar
bound state , earlier predicted by C.D. Froggatt, H.B. Nielsen
and L.V. Laperashvili, we try to provide the vacuum stability in the SM and
exact accuracy of the MPP.Comment: 37 pages and 7 figures. arXiv admin note: text overlap with
arXiv:1601.03231; text overlap with arXiv:1302.2716 by other author
Comparison of perturbative expansions using different phonon bases for two-site Holstein model
The two-site single-polaron problem is studied within the perturbative
expansions using different standard phonon basis obtained through the Lang
Firsov (LF), modified LF (MLF) and modified LF transformation with squeezed
phonon states (MLFS). The role of these convergent expansions using the above
prescriptions in lowering the energy and in determining the correlation
functions are compared for different values of coupling strength. The
single-electron energy, oscillator wave functions and correlation functions are
calculated for the same system. The applicability of different phonon basis in
different regimes of the coupling strength as well as in different regimes of
hopping are also discussed.Comment: 24 pages (RevTEX), 12 postscript figures, final version accepted in
PRB(2000) Jornal Ref: Phys. Rev. B, 61, 4592-4602 (2000
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