266 research outputs found
The Implications of the Microwave Background Anisotropies for Laser-Interferometer-Tested Gravitational Waves
The observed microwave background anisotropies in combination with the theory
of quantum mechanically generated cosmological perturbations predict a well
measurable amount of relic gravitational waves in the frequency intervals
tested by LISA and ground-based laser interferometers.Comment: revised, corrected, and slightly expanded version to be published in
Classical and Quantum Gravity; 22 pages, 1 Postscript figure, Latex; Based on
a talk presented at the First Internationsl LISA Symposium, 9 - 12 July 1996,
RAL, U
Extracting V_{ub} Without Recourse to Structure Functions
We present a closed form expression for |V_{ub}|^2/ |V_{tb} V_{ts}^*|^2 in
terms of the endpoint photon and lepton spectra from the inclusive decays B ->
X_s\gamma and B -> X_u\ell\nu, respectively, which includes the resummation of
the endpoint logs at next to leading order and is completely independent of the
B meson structure function. The use of this expression for extracting V_{ub}
would eliminate the large systematic errors usually incurred due to the
modeling of the heavy quarks' Fermi motion.Comment: 20 pages, no figures, minor typos correcte
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
Conformal Invariance and Cosmic Background Radiation
The spectrum and statistics of the cosmic microwave background radiation
(CMBR) are investigated under the hypothesis that scale invariance of the
primordial density fluctuations should be promoted to full conformal
invariance. As in the theory of critical phenomena, this hypothesis leads in
general to deviations from naive scaling. The spectral index of the two-point
function of density fluctuations is given in terms of the quantum trace anomaly
and is greater than one, leading to less power at large distance scales than a
strict Harrison-Zel'dovich spectrum. Conformal invariance also implies
non-gaussian statistics for the higher point correlations and in particular, it
completely determines the large angular dependence of the three-point
correlations of the CMBR.Comment: 4 pages, Revtex file, uuencoded with one figur
Solvable Models of Domain Walls in N=1 Supergravity
A class of exactly solvable models of domain walls are worked out in D=4
supergravity. We develop a method to embed globally supersymmetric
theories with exact BPS domain wall solutions into supergravity, by introducing
a gravitationally deformed superpotential. The gravitational deformation is
natural in the spirit of maintaining the K\"ahler invariance. The solutions of
the warp factor and the Killing spinor are also obtained. We find that three
distinct behaviors of warp factors arise depending on the value of a constant
term in the superpotential : exponentially decreasing in both sides of the
wall, flat in one side and decreasing in the other, and increasing in one side
and decreasing in the other. Only the first possibility gives the localized
massless graviton zero mode. Models with multi-walls and models with runaway
vacua are also discussed.Comment: 10 pages, 3 figures; Misprints in three formulas are correcte
Degenerate Domain Wall Solutions in Supersymmetric Theories
A family of degenerate domain wall configurations, partially preserving
supersymmetry, is discussed in a generalized Wess-Zumino model with two scalar
superfields. We establish some general features inherent to the models with
continuously degenerate domain walls. For instance, for purely real
trajectories additional "integrals of motion" exist. The solution for the
profile of the scalar fields for any wall belonging to the family is found in
quadratures for arbitrary ratio of the coupling constants. For a special value
of this ratio the solution family is obtained explicitly in terms of elementary
functions. We also discuss the threshold amplitudes for multiparticle
production generated by these solutions. New unexpected nullifications of the
threshold amplitudes are found.Comment: 21 pages, LaTeX, 3 figures using epsf.st
Counting Domain Walls in N=1 Super Yang-Mills Theory
We study the multiplicity of BPS domain walls in N=1 super Yang-Mills theory,
by passing to a weakly coupled Higgs phase through the addition of fundamental
matter. The number of domain walls connecting two specified vacuum states is
then determined via the Witten index of the induced worldvolume theory, which
is invariant under the deformation to the Higgs phase. The worldvolume theory
is a sigma model with a Grassmanian target space which arises as the coset
associated with the global symmetries broken by the wall solution. Imposing a
suitable infrared regulator, the result is found to agree with recent work of
Acharya and Vafa in which the walls were realized as wrapped D4-branes in IIA
string theory.Comment: 28 pages, RevTeX, 3 figures; v2: discussion of the index slightly
expanded, using an alternative regulator, and references added; v3: typos
corrected, to appear in Phys. Rev.
Testing of CP, CPT and causality violation with the light propagation in vacuum in presence of the uniform electric and magnetic fields
We have considered the structure of the fundamental symmetry violating part
of the photon refractive index in vacuum in the presence of constant electric
and magnetic fields. This part of the refractive index can, in principle,
contain CPT symmetry breaking terms. Some of the terms violate Lorentz
invariance, whereas the others violate locality and causality. Estimates of
these effects, using laser experiments are considered.Comment: 12 page
Anomaly and quantum corrections to solitons in two-dimensional theories with minimal supersymmetry
We reexamine the issue of the soliton mass in two-dimensional models with N
=1 supersymmetry. The superalgebra has a central extension, and at the
classical level the soliton solution preserves 1/2 of supersymmetry which is
equivalent to BPS saturation. We prove that the property of BPS saturation,
i.e. the equality of the soliton mass to the central charge, remains intact at
the quantum level in all orders of the weak coupling expansion. Our key finding
is an anomaly in the expression for the central charge. The classical central
charge, equal to the jump of the superpotential, is amended by an anomalous
term proportional to the second derivative of the superpotential. The anomaly
is established by various methods in explicit one-loop calculations. We argue
that this one-loop result is not affected by higher orders. We discuss in
detail how the impact of the boundary conditions can be untangled from the
soliton mass calculation. In particular, the soliton profile and the energy
distribution are found at one loop. A "supersymmetry" in the soliton mass
calculations in the non-supersymmetric models is observed.Comment: 50 pages, LaTex, 2 figures. The version exactly matching that
published in Phys.Rev. D. The most essential addition is a footnote,
clarifying multiplet shortenin
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