32 research outputs found
Multipole moments in Kaluza-Klein theories
This paper contains discussion of the problem of motion of extended i.e. non
point test bodies in multidimensional space. Extended bodies are described in
terms of so called multipole moments. Using approximated form of equations of
motion for extended bodies deviation from geodesic motion is derived. Results
are applied to special form of space-time.Comment: 11 pages, AMS-TeX, few misprints corrected, to appear in Classical
and Quantum Gravit
Green functions and dimensional reduction of quantum fields on product manifolds
We discuss Euclidean Green functions on product manifolds P=NxM. We show that
if M is compact then the Euclidean field on P can be approximated by its zero
mode which is a Euclidean field on N. We estimate the remainder of this
approximation. We show that for large distances on N the remainder is small. If
P=R^{D-1}xS^{beta}, where S^{beta} is a circle of radius beta, then the result
reduces to the well-known approximation of the D dimensional finite temperature
quantum field theory to D-1 dimensional one in the high temperature limit.
Analytic continuation of Euclidean fields is discussed briefly.Comment: 17 page
Optical Activity From Extra Dimension
Optical activity, like Faraday effect, is a rotation of the plane of
polarization of propagating light in a medium and can be attributed to
different sources with distinct signatures. In this note we discuss the effect
of optical activity {\it{in vacuum}} due to Kaluza-Klein scalar field ,
in the presence of an external electro-magnetic field. The astrophysical
implication of this effect is indicated. We also point out the possibility of
observing the same in laboratory conditions.Comment: Four Page
Particle creation in the presence of a warped extra dimension
Particle creation in spacetimes with a warped extra dimension is studied. In
particular, we investigate the dynamics of a conformally coupled, massless
scalar field in a five dimensional warped geometry where the induced metric on
the 3--branes is that of a spatially flat cosmological model. We look at
situations where the scale of the extra dimension is assumed (i) to be time
independent or (ii) to have specific functional forms for time dependence. The
warp factor is chosen to be that of the Randall--Sundrum model. With particular
choices for the functional form of the scale factor (and also the function
characterising the time evolution of the extra dimension) we obtain the , the particle number and energy densities after solving (wherever
possible, analytically but, otherwise, numerically) the conformal scalar field
equations. The behaviour of these quantities for the massless and massive
Kaluza--Klein modes are examined. Our results show the effect of a warped extra
dimension on particle creation and illustrate how the nature of particle
production on the brane depends on the nature of warping, type of cosmological
evolution as well as the temporal evolution of the extra dimension.Comment: 21 pages, 10 figures, minor corrections, new references added,
version to appear in JCA
Detectability of Strange Matter in Heavy Ion Experiments
We discuss the properties of two distinct forms of hypothetical strange
matter, small lumps of strange quark matter (strangelets) and of hyperon matter
(metastable exotic multihypernuclear objects: MEMOs), with special emphasis on
their relevance for present and future heavy ion experiments. The masses of
small strangelets up to A = 40 are calculated using the MIT bag model with
shell mode filling for various bag parameters. The strangelets are checked for
possible strong and weak hadronic decays, also taking into account multiple
hadron decays. It is found that strangelets which are stable against strong
decay are most likely highly negative charged, contrary to previous findings.
Strangelets can be stable against weak hadronic decay but their masses and
charges are still rather high. This has serious impact on the present high
sensitivity searches in heavy ion experiments at the AGS and CERN facilities.
On the other hand, highly charged MEMOs are predicted on the basis of an
extended relativistic mean-field model. Those objects could be detected in
future experiments searching for short-lived, rare composites. It is
demonstrated that future experiments can be sensitive to a much wider variety
of strangelets.Comment: 26 pages, 5 figures, uses RevTeX and epsf.st
Non-perturbative dynamics of hot non-Abelian gauge fields: beyond leading log approximation
Many aspects of high-temperature gauge theories, such as the electroweak
baryon number violation rate, color conductivity, and the hard gluon damping
rate, have previously been understood only at leading logarithmic order (that
is, neglecting effects suppressed only by an inverse logarithm of the gauge
coupling). We discuss how to systematically go beyond leading logarithmic order
in the analysis of physical quantities. Specifically, we extend to
next-to-leading-log order (NLLO) the simple leading-log effective theory due to
Bodeker that describes non-perturbative color physics in hot non-Abelian
plasmas. A suitable scaling analysis is used to show that no new operators
enter the effective theory at next-to-leading-log order. However, a NLLO
calculation of the color conductivity is required, and we report the resulting
value. Our NLLO result for the color conductivity can be trivially combined
with previous numerical work by G. Moore to yield a NLLO result for the hot
electroweak baryon number violation rate.Comment: 20 pages, 1 figur
Nonforward Parton Distributions
Applications of perturbative QCD to deeply virtual Compton scattering and
hard exclusive electroproduction processes require a generalization of usual
parton distributions for the case when long-distance information is accumulated
in nonforward matrix elements of quark and gluon light-cone operators.
We describe two types of nonperturbative functions parametrizing such matrix
elements: double distributions F(x,y;t) and nonforward distribution functions
F_\zeta (X;t), discuss their spectral properties, evolution equations which
they satisfy, basic uses and general aspects of factorization for hard
exclusive processes.Comment: Final version, to be published in Phys.Rev.
The Cosmological Constant Problem and Quintessence
I briefly review the cosmological constant problem and the issue of dark
energy (or quintessence). Within the framework of quantum field theory, the
vacuum expectation value of the energy momentum tensor formally diverges as
. A cutoff at the Planck or electroweak scale leads to a cosmological
constant which is, respectively, or times larger than the
observed value, \l/8\pi G \simeq 10^{-47} GeV. The absence of a
fundamental symmetry which could set the value of \l to either zero or a very
small value leads to {\em the cosmological constant problem}. Most cosmological
scenario's favour a large time-dependent \l-term in the past (in order to
generate inflation at ), and a small \l-term today, to account
for the current acceleration of the universe at z \lleq 1. Constraints
arising from cosmological nucleosynthesis, CMB and structure formation
constrain \l to be sub-dominant during most of the intermediate epoch
. This leads to the {\em cosmic coincidence} conundrum which
suggests that the acceleration of the universe is a recent phenomenon and that
we live during a special epoch when the density in \l and in matter are
almost equal. Time varying models of dark energy can, to a certain extent,
ameliorate the fine tuning problem (faced by \l), but do not resolve the
puzzle of cosmic coincidence. I briefly review tracker models of dark energy,
as well as more recent brane inspired ideas and the issue of horizons in an
accelerating universe. Model independent methods which reconstruct the cosmic
equation of state from supernova observations are also assessed. Finally, a new
diagnostic of dark energy -- `Statefinder', is discussed.Comment: Minor typo's corrected, references added and updated. 15 pages, 5
figures. Invited review at ``The Early Universe and Cosmological
Observations: a Critical Review'', UCT, Cape Town, July 2001, to appear in
"Classical and Quantum Gravity
correction to pseudoscalar quarkonium decay to two photons
We investigate the correction to the process of
pseudoscalar quarkonium decay to two photons in nonrelativistic QCD (NRQCD)
factorization framework. The short-distance coefficient associated with the
relative-order NRQCD matrix element is determined to next-to-leading
order in through the perturbative matching procedure. Some technical
subtleties encountered in calculating the {O(\alpha_s) QCD amplitude are
thoroughly addressed.Comment: v2, 28 pages, 2 figures and 2 tables, matching the published version;
typos corrected, references added, as well as a "Note added in the proof
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe