204 research outputs found
Nonlinear Evolution of Anisotropic Cosmological Power
There has been growing interest in the possibility of testing more precisely
the assumption of statistical isotropy of primordial density perturbations. If
it is to be tested with galaxy surveys at distance scales <~ 10 Mpc, then
nonlinear evolution of anisotropic power must be understood. To this end, we
calculate the angular dependence of the power spectrum to third order in
perturbation theory for a primordial power spectrum with a quadrupole
dependence on the wavevector direction. Our results suggest that primordial
power anisotropies will be suppressed by <~ 7% in the quasilinear regime. We
also show that the skewness in the statistically anisotropic theory differs by
no more than 1% from that in the isotropic theory.Comment: 4 pages, 1 figure; accepted for publication in Physical Review
Letter
Domain walls in supersymmetric QCD: from weak to strong coupling
We consider domain walls that appear in supersymmetric QCD with Nf < Nc
massive flavours. In particular, for 2 Nf < Nc we explicitly construct the
domain walls that interpolate between vacua labeled by i and (i+ N_f). We show
that these solutions are Bogomol'nyi-Prasad-Sommerfield (BPS) saturated for any
value of the mass of the matter fields. This fact allows us to evaluate the
large mass limit of these domain walls. We comment on the relevance of these
solutions for supersymmetric gluodynamics.Comment: 4 pages, 4 figures, LaTex, uses psfig.st
N=2 Sigma Model with Twisted Mass and Superpotential: Central Charges and Solitons
We consider supersymmetric sigma models on the Kahler target spaces, with
twisted mass. The Kahler spaces are assumed to have holomorphic Killing
vectors. Introduction of a superpotential of a special type is known to be
consistent with N=2 superalgebra (Alvarez-Gaume and Freedman). We show that the
algebra acquires central charges in the anticommutators {Q_L, Q_L} and {Q_R,
Q_R}. These central charges have no parallels, and they can exist only in two
dimensions. The central extension of the N=2 superalgebra we found paves the
way to a novel phenomenon -- spontaneous breaking of a part of supersymmetry.
In the general case 1/2 of supersymmetry is spontaneously broken (the vacuum
energy density is positive), while the remaining 1/2 is realized linearly. In
the model at hand the standard fermion number is not defined, so that the
Witten index as well as the Cecotti-Fendley-Intriligator-Vafa index are
useless. We show how to construct an index for counting short multiplets in
internal algebraic terms which is well-defined in spite of the absence of the
standard fermion number. Finally, we outline derivation of the quantum anomaly
in {\bar Q_L, Q_R}.Comment: 21 pages, Latex, 1 eps figure. Two important references adde
Cosmological status of Lagrangian theory of density perturbations
We show that hydrodynamical and field approaches in theory of cosmological
scalar perturbations are equivalent for a single medium. We also give relations
between notations introduced by V. Lukash, J. Bardeen, J. Bardeen et al. and G.
Chibisov and V. Mukhanov.Comment: 8 pages, no figures, submitted to Astronomy Report
Fluid phonons and inflaton quanta at the protoinflationary transition
Quantum and thermal fluctuations of an irrotational fluid are studied across
the transition regime connecting a protoinflationary phase of decelerated
expansion to an accelerated epoch driven by a single inflaton field. The
protoinflationary inhomogeneities are suppressed when the transition to the
slow roll phase occurs sharply over space-like hypersurfaces of constant energy
density. If the transition is delayed, the interaction of the quasi-normal
modes related, asymptotically, to fluid phonons and inflaton quanta leads to an
enhancement of curvature perturbations. It is shown that the dynamics of the
fluctuations across the protoinflationary boundaries is determined by the
monotonicity properties of the pump fields controlling the energy transfer
between the background geometry and the quasi-normal modes of the fluctuations.
After corroborating the analytical arguments with explicit numerical examples,
general lessons are drawn on the classification of the protoinflationary
transition.Comment: 30 pages, 3 figure
Lessons from : Vacuum structure, Asymptotic Series, Instantons and all that
We discuss two dimensional with fermions in the
fundamental as well as adjoint representation. We find factorial growth in the coefficients of
the large order perturbative expansion. We argue that this behavior is related
to classical solutions of the theory, instantons, thus it has nonperturbative
origin. Phenomenologically such a growth is related to highly excited states in
the spectrum. We also analyze the heavy-light quark system within
operator product expansion (which it turns out to be an asymptotic series).
Some vacuum condensates \la\bar{q}(x_{\mu}D_{\mu})^{2n}q\ra\sim (x^2)^n\cdot
n! which are responsible for this factorial growth are also discussed. We
formulate some general puzzles which are not specific for 2D physics, but are
inevitable features of any asymptotic expansion. We resolve these apparent
puzzles within and we speculate that analogous puzzles might occur in
real 4-dimensional QCD as well.Comment: latex, 26 pages. A final version to appear in Phys. Rev.
6 + 1 Vacua in Supersymmetric QCD with G_2 Gauge Group
We consider N=1 supersymmetric QCD based on the G_2 gauge group and including
3 chiral matter 7-plets. In that case, the gauge symmetry is broken completely
and the instanton-generated superpotential on the classical moduli space is
present. If the theory involves the Yukawa term, there are six chirally
asymmetric vacua. In the limit when the Yukawa coupling vanishes, two of the
vacua run away to infinity and only 4 asymmetric vacuum states are left.
Besides, a chirally symmetric state is always present. We consider also an O(7)
model with 4 chiral multiplets in spinor representation. In that case, there
are 4 extra "virtual vacua" dwelling at infinity of the moduli space. In a
non-renormalizable theory involving a quartic term in the superpotential, they
show up at finite moduli values.Comment: 15 pages LaTeX, 1 Postscript figur
Hard diffractive electroproduction, transverse momentum distribution and QCD vacuum structure
We study the impact of the "intrinsic" hadron transverse momentum on the
pre-asymptotic behavior of the diffractive electroproduction of longitudinally
polarized -meson. Surprisingly, we find the onset of the asymptotic
regime in this problem to be rather low, Q^2 ~ 10 GeV^2 where power corrections
due to the transverse momentum do not exceed 20 % in the amplitude. This
drastically contrasts with exclusive amplitudes where the asymptotics starts at
much higher Q^2 = 50 - 100 GeV^2. The sources of such unexpected behavior are
traced back to some general (the quark-hadron duality) as well as more silent
(properties of higher dimensional vacuum condensates) features of QCD.Comment: 27 pages (LaTex), 1 figure (epsfig
Normal modes for metric fluctuations in a class of higher-dimensional backgrounds
We discuss a gauge invariant approach to the theory of cosmological
perturbations in a higher-dimensonal background. We find the normal modes which
diagonalize the perturbed action, for a scalar field minimally coupled to
gravity, in a higher-dimensional manifold M of the Bianchi-type I, under the
assumption that the translations along an isotropic spatial subsection of M are
isometries of the full, perturbed background. We show that, in the absence of
scalar field potential, the canonical variables for scalar and tensor metric
perturbations satisfy exactly the same evolution equation, and we discuss the
possible dependence of the spectrum on the number of internal dimensions.Comment: 19 pages, LATEX, an explicit example is added to discuss the possible
dependence of the perturbation spectrum on the number of internal dimensions.
To apper in Class. Quantum Gra
Hormone secreted by the pineal gland - melatonin feedsideward involvement in cancer growth
Here the presence of a chronomodulating actions of melatonin via feedsideawards mechanism in vitro as well as, in vivo, in two experimental models was presented. Intriguing process of how this takes place may due to an interacting pineal pituitary-adrenal networks (1). In vivo studies confirmed the role of melatonin in the study on Meth-A-sarcoma in mice and in LOU tumor growth. Melatonin disrupted circadian time structure of in vivo tumor growth on a feedsideawards manner in the case of the immunocytoma growth in female inoculated rats. Low doses disrupted the circadian DNA synthesis of mF-cells. Drug delivery systems must be taken in consideration the role of melatonin feedsideawards involvement during chronomodulated therapy of cancer patients
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