1,416 research outputs found
The (pseudo)issue of the conformal frame revisited
The issue of the equivalence between Jordan and Einstein conformal frames in
scalar-tensor gravity is revisited, with emphasis on implementing running units
in the latter. The lack of affine parametrization for timelike worldlines and
the cosmological constant problem in the Einstein frame are clarified, and a
paradox in the literature about cosmological singularities appearing only in
one frame is solved. While, classically, the two conformal frames are
physically equivalent, they seem to be inequivalent at the quantum level.Comment: 29 pages, latex, to appear in Phys. Rev.
The Exact Evolution Equation of the Curvature Perturbation for Closed Universe
As is well known, the exact evolution equation of the curvature perturbation
plays a very important role in investigation of the inflation power spectrum of
the flat universe. However, its corresponding exact extension for the non-flat
universes has not yet been given out clearly. The interest in the non-flat,
specially closed, universes is being aroused recently. The need of this
extension is pressing. We start with most elementary physical consideration and
obtain finally this exact evolution equation of the curvature perturbation for
the non-flat universes, as well as the evolutionary controlling parameter and
the exact expression of the variable mass in this equation. We approximately do
a primitive and immature analysis on the power spectrum of non-flat universes.
This analysis shows that this exact evolution equation of the curvature
perturbation for the non-flat universes is very complicated, and we need to do
a lot of numerical and analytic work for this new equation in future in order
to judge whether the universe is flat or closed by comparison between theories
and observations.Comment: 10 pages, no figures, Late
Two-photon correlations as a sign of sharp transition in quark-gluon plasma
The photon production arising due to time variation of the medium has been
considered. The Hamilton formalism for photons in time-variable medium (plasma)
has been developed with application to inclusive photon production. The results
have been used for calculation of the photon production in the course of
transition from quark-gluon phase to hadronic phase in relativistic heavy ion
collisions. The relative strength of the effect as well as specific two- photon
correlations have been evaluated. It has been demonstrated that the opposite
side two-photon correlations are indicative of the sharp transition from the
quark-gluon phase to hadrons.Comment: 23 pages, 2 figure
Signal and Backgrounds for Leptoquarks at the LHC
We study the potentiality of the CERN Large Hadron Collider (LHC) to unravel
the existence of first generation scalar leptoquarks.
Working with the most general invariant leptoquark
interactions, we analyze in detail the signals and backgrounds that lead to a
final state containing a pair and jets. Our results indicate that a
machine like the LHC will be able to discover leptoquarks with masses up to
2--3 TeV depending on their couplings.Comment: 37 pages, revtex, uses epsfig.sty (included), 15 figures (included
Interactions between downslope flows and a developing cold-air pool
A numerical model has been used to characterize the development of a region of enhanced cooling in an alpine valley with a width of order (Formula presented.) km, under decoupled stable conditions. The region of enhanced cooling develops largely as a region of relatively dry air which partitions the valley atmosphere dynamics into two volumes, with airflow partially trapped within the valley by a developing elevated inversion. Complex interactions between the region of enhanced cooling and the downslope flows are quantified. The cooling within the region of enhanced cooling and the elevated inversion is almost equally partitioned between radiative and dynamic effects. By the end of the simulation, the different valley atmospheric regions approach a state of thermal equilibrium with one another, though this cannot be said of the valley atmosphere and its external environment.Peer reviewe
Soft Electromagnetic Radiations From Equilibrating Quark-Gluon Plasma
We evaluate the bremsstrahlung production of low mass dileptons and soft
photons from equilibrating and transversely expanding quark gluon plasma which
may be created in the wake of relativistic heavy ion collisions. We use initial
conditions obtained from the self screened parton cascade model. We consider a
boost invariant longitudinal and cylindrically symmetric transverse expansion
of the parton plasma and find that for low mass dileptons ( GeV)
and soft photons ( GeV), the bremsstrahlung contribution is
rather large compared to annihilation process at both RHIC and LHC energies. We
also find an increase by a factor of 15-20 in the low mass dileptons and soft
photons yield as one goes from RHIC to LHC energies.Comment: 8 pages, including 7 figures To appear in Phys. Rev.
Much Ado About Leptoquarks: A Comprehensive Analysis
We examine the phenomenological implications of a 200 GeV leptoquark in light
of the recent excess of events at HERA. Given the relative predictions of
events rates in e^+p versus e^-p, we demonstrate that classes of leptoquarks
may be excluded, including those contained in E_6 GUT models. It is shown that
future studies with polarized beams at HERA could reveal the chirality of the
leptoquark fermionic coupling and that given sufficient luminosity in each
e^\pm_{L,R} channel the leptoquark quantum numbers could be determined. The
implications of 200-220 GeV leptoquarks at the Tevatron are examined. While
present Tevatron data most likely excludes vector leptoquarks and leptogluons
in this mass region, it does allow for scalar leptoquarks. We find that while
leptoquarks have little influence on Drell-Yan production, further studies at
the Main Injector are possible in the single production channel. We investigate
precision electroweak measurements as well as the process e^+e^-\to q\bar q at
LEP II and find they provide no further restrictions on these leptoquark
models. We then ascertain that cross section and polarization asymmetry
measurements at the NLC provide the only direct mechanism to determine the
leptoquark's electroweak quantum numbers. The single production of leptoquarks
in \gamma e collisions by both the backscattered laser and Weisacker-Williams
techniques at the NLC is also discussed. Finally, we demonstrate that we can
obtain successful coupling constant unification in models with leptoquarks,
both with or without supersymmetry. The supersymmetric case requires the GUT
group to be larger than SU(5) such as flipped SU(5)\times U(1)_X.Comment: Corrected single production cross section at Tevatron, updated atomic
parity violation constraints, 55 page
Signal and Backgrounds for Leptoquarks at the LHC II: Vector Leptoquarks
We perform a detailed analyses of the CERN Large Hadron Collider (LHC)
capability to discover first generation vector leptoquarks through their pair
production. We study the leptoquark signals and backgrounds that give rise to
final states containing a pair e+e- and jets. Our results show that the LHC
will be able to discover vector leptoquarks with masses up to 1.3-2.1 TeV
depending on their couplings to fermions and gluons.Comment: 18 pages, 3 figures, REVTe
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