799 research outputs found
The decay omega(782) -> 5 pi in chiral theory
The arguments are put forward that the many pion decays omega ->2 pi^+ 2 pi^-
pi^0 and pi^+ pi^- 3 pi^0 provide an ideal test site for testing the
predictions of chiral models of the vector meson decays into many pions. Using
the approach based on the Weinberg Lagrangian or, in a new language, the
Lagrangian of hidden local symmetry added with the term induced by the
anomalous Lagrangian of Wess and Zumino, the partial widths of these decays are
evaluated, and their excitation curves in e^+e^- annihilation are obtained. The
discussed are the perspectives of the experimental study of the decays omega ->
5 pi in e^+e^- annihilation and photoproduction.Comment: revtex, 12 pages include 2 ps figures; clarifying remarks and
references added, 17-fold reduction of filesize of fig1.ps. Accepted in Phys.
Lett.
Delayed Reheating and the Breakdown of Coherent Oscillations
We analyze the evolution of the perturbations in the inflaton field and
metric following the end of inflation. We present accurate analytic
approximations for the perturbations, showing that the coherent oscillations of
the post-inflationary condensate necessarily break down long before any current
phenomenological constraints require the universe to become radiation
dominated. Further, the breakdown occurs on length-scales equivalent to the
comoving post-inflationary horizon size. This work has implications for both
the inflationary "matching" problem, and the possible generation of a
stochastic gravitational wave background in the post-inflationary universe.Comment: 18 pages, 5 figures, v2: references added, extended discussion in
section
The Rho-Meson as a Collective Excitation
A model of the rho-meson as a collective excitation of pairs in a
system that obeys the modified Nambu--Jona-Lasinio Lagrangian is proposed. The
rho emerges as a dormant Goldstone boson. The origin of the rho-meson mass is
understood as a result of spontaneous chiral symmetry breaking. The low-energy
dynamics of rho, pi, omega and gamma is consistently described in this new
framework. The model accounts for the origin of the celebrated
Kawarabayashi--Suzuki--Riazuddin--Fayyazuddin relation.Comment: 8 pages, plain LaTe
The Momentum--Space Bosonization of the Nambu--Jona-Lasinio Model with Vector and Axial-Vector Mesons
The momentum-space bosonization method is extended to the case of a
Nambu--Jona-Lasinio type model with vector and axial-vector mesons. The method
presented gives the possibility of deriving any meson vertex function to all
orders in momenta and to the leading order in . Two-point functions,
which describe one-particle transitions to the hadronic vacuum, and meson
self-energies are considered. We find new relations which generalize the
well-known KSFR relation and both the first and the second Weinberg sum rules.
These result from a consistent treatment of higher order terms in the momentum
expansion.Comment: 11pp, TeX, CRN 93-5
Computing the Primordial Power Spectra Directly
The tree order power spectra of primordial inflation depend upon the
norm-squared of mode functions which oscillate for early times and then freeze
in to constant values. We derive simple differential equations for the power
spectra, that avoid the need to numerically simulate the physically irrelevant
phases of the mode functions. We also derive asymptotic expansions which should
be valid until a few e-foldings before first horizon crossing, thereby avoiding
the need to evolve mode functions from the ultraviolet over long periods of
inflation.Comment: 11 pages, uses LaTex2
Light Quark Masses in Multi-Quark Interactions
We suggest and discuss in detail a multi-quark three flavor Lagrangian of the
Nambu -- Jona-Lasinio type, which includes a set of effective interactions
proportional to the current quark masses. It is shown that within the dynamical
chiral symmetry breaking regime, the masses of the pseudo Goldstone bosons and
their chiral partners, members of the low lying scalar nonet, are in perfect
agreement with current phenomenological expectations. The role of the new
interactions is analyzed.Comment: 8 pages, published versio
Conformal Symmetries of Adiabatic Modes in Cosmology
We remark on the existence of non-linearly realized conformal symmetries for
scalar adiabatic perturbations in cosmology. These conformal symmetries are
present for any cosmological background, beyond any slow-roll or quasi-de
Sitter approximation. The dilatation transformation shifts the curvature
perturbation by a constant, and corresponds to the well-known symmetry under
spatial rescaling. We argue that the scalar sector is also invariant under
special conformal transformations, which shift the curvature perturbation by a
term linear in the spatial coordinates. We discuss whether these conformal
symmetries can be extended to include tensor perturbations. Tensor modes
introduce their own set of non-linearly realized symmetries. We identify an
infinite set of large gauge transformations which maintain the transverse,
traceless gauge condition, while shifting the tensor mode non-trivially.Comment: 16 page
Damping of Tensor Modes in Cosmology
An analytic formula is given for the traceless transverse part of the
anisotropic stress tensor due to free streaming neutrinos, and used to derive
an integro-differential equation for the propagation of cosmological
gravitational waves. The solution shows that anisotropic stress reduces the
squared amplitude by 35.6 % for wavelengths that enter the horizon during the
radiation-dominated phase, independent of any cosmological parameters. This
decreases the tensor temperature and polarization correlation functions for
these wavelengths by the same amount. The effect is less for wavelengths that
enter the horizon at later times. At the longest wavelengths the decrease in
the tensor correlation functions due to neutrino free streaming ranges from
10.7% for to 9.0% for . An Appendix gives a
general proof that tensor as well as scalar modes satisfy a conservation law
for perturbations outside the horizon, even when the anisotropic stress tensor
is not negligible.Comment: 14 pages. The original version of this paper has been expanded to
deal with perturbations of any wavelength. While for wavelengths short enough
to enter the horizon during radiation dominance, temperature and polarization
correlations are damped by 35.6%, at the longest wavelengths the damping is
from 9.0% to 11%. An added Appendix gives a general proof that tensor as well
as scalar modes satisfy a conservation law outside the horizon, even during
neutrino decoupling. Some references are also adde
Fluctuations in the Cosmic Microwave Background I: Form Factors and their Calculation in Synchronous Gauge
It is shown that the fluctuation in the temperature of the cosmic microwave
background in any direction may be evaluated as an integral involving scalar
and dipole form factors, which incorporate all relevant information about
acoustic oscillations before the time of last scattering. A companion paper
gives asymptotic expressions for the multipole coefficient in terms of
these form factors. Explicit expressions are given here for the form factors in
a simplified hydrodynamic model for the evolution of perturbations.Comment: 35 pages, no figures. Improved treatment of damping, including both
Landau and Silk damping; inclusion of late-time effects; several references
added; minor changes and corrections made. Accepted for publication in Phys.
Rev. D1
On semiclassical approximation and spinning string vertex operators in AdS_5 x S^5
Following earlier work by Polyakov and Gubser, Klebanov and Polyakov, we
attempt to clarify the structure of vertex operators representing string states
which have large (``semiclassical'') values of AdS energy (equal to 4-d
dimension \Delta) and angular momentum J in S^5 or spin S in AdS_5. We comment
on the meaning of semiclassical limit in the context of \alpha' perturbative
expansion for the 2-d anomalous dimensions of the corresponding vertex
operators. We consider in detail the leading-order 1-loop renormalization of
these operators in AdS_5 x S^5 sigma model (ignoring fermionic contributions).
We find new examples of operators for which, as in the case considered in
hep-th/0110196, the 1-loop anomalous dimension can be made small by tuning
quantum numbers. We also comment on a possibility of deriving the semiclassical
relation between \Delta and J or S from the marginality condition for the
vertex operators, using a stationary phase approximation in the path integral
expression for their 2-point correlator on a complex plane.Comment: 35 pages, harvmac; v2: references adde
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