36,519 research outputs found
Scalar Glueball--Quarkonium Mixing and the Structure of the QCD Vacuum
We use Ward identities of broken scale invariance to infer the amount of
scalar glueball-- meson mixing from the ratio of quark and gluon
condensates in the QCD vacuum. Assuming dominance by a single scalar state, as
suggested by a phase-shift analysis, we find a mixing angle , corresponding to near-maximal mixing of the glueball and
components.Comment: 7 pages, LaTe
Neutrino Oscillations Induced by Gravitational Recoil Effects
Quantum gravitational fluctuations of the space-time background, described by
virtual D branes, may induce neutrino oscillations if a tiny violation of the
Lorentz invariance (or a violation of the equivalence principle) is imposed. In
this framework, the oscillation length of massless neutrinos turns out to be
proportional to M/E^2, where E is the neutrino energy and M is the mass scale
characterizing the topological fluctuations in the vacuum. Such a functional
dependence on the energy is the same obtained in the framework of loop quantum
gravity.Comment: 5 pages, LaTex fil
An Analysis of Diffraction in Deep-Inelastic Scattering
We propose a simple parametrization for the deep-inelastic diffractive cross
section. It contains the contribution of production to both the
longitudinal and the transverse diffractive structure functions, and of the
production of final states from transverse photons. We start from
the hard region and perform a suitable extrapolation into the soft region. We
test our model on the 1994 ZEUS and H1 data, and confront it with the H1
conjecture of a singular gluon distribution.Comment: 24 pages, LaTeX, figures included using epsfi
Dark Matter in SuperGUT Unification Models
After a brief update on the prospects for dark matter in the constrained
version of the MSSM (CMSSM) and its differences with models based on minimal
supergravity (mSUGRA), I will consider the effects of unifying the
supersymmetry-breaking parameters at a scale above M_{GUT}. One of the
consequences of superGUT unification, is the ability to take vanishing scalar
masses at the unification scale with a neutralino LSP dark matter candidate.
This allows one to resurrect no-scale supergravity as a viable phenomenological
model.Comment: 12 pages, 16 figures, To be published in the Proceedings of the 6th
DSU Conference, Leon, Mexico, ed. D. Delepin
Astrophysical Probes of the Constancy of the Velocity of Light
We discuss possible tests of the constancy of the velocity of light using
distant astrophysical sources such as gamma-ray bursters (GRBs), Active
Galactic Nuclei (AGNs) and pulsars. This speculative quest may be motivated by
some models of quantum fluctuations in the space-time background, and we
discuss explicitly how an energy-dependent variation in photon velocity \delta
c/ c \sim - E / M arises in one particular quantum-gravitational model. We then
discuss how data on GRBs may be used to set limits on variations in the
velocity of light, which we illustrate using BATSE and OSSE observations of the
GRBs that have recently been identified optically and for which precise
redshifts are available. We show how a regression analysis can be performed to
look for an energy-dependent effect that should correlate with redshift. The
present data yield a limit M \gsim 10^{15} GeV for the quantum gravity scale.
We discuss the prospects for improving this analysis using future data, and how
one might hope to distinguish any positive signal from astrophysical effects
associated with the sources.Comment: 37 pages LaTeX, 9 eps figures included, uses aasms4.st
Stochastic compartmental analysis - Some applications and examples of estimation in a pulse labelled system
Stochastic compartmental analysis with examples of estimation in pulse labelled syste
Non-Critical Liouville String Escapes Constraints on Generic Models of Quantum Gravity
It has recently been pointed out that generic models of quantum gravity must
contend with severe phenomenological constraints imposed by gravitational
Cerenkov radiation, neutrino oscillations and the cosmic microwave background
radiation. We show how the non-critical Liouville-string model of quantum
gravity we have proposed escapes these constraints. It gives energetic
particles subluminal velocities, obviating the danger of gravitational Cerenkov
radiation. The effect on neutrino propagation is naturally flavour-independent,
obviating any impact on oscillation phenomenology. Deviations from the expected
black-body spectrum and the effects of time delays and stochastic fluctuations
in the propagation of cosmic microwave background photons are negligible, as
are their effects on observable spectral lines from high-redshift astrophysical
objects.Comment: 15 pages LaTeX, 2 eps figures include
Integrability of irrotational silent cosmological models
We revisit the issue of integrability conditions for the irrotational silent
cosmological models. We formulate the problem both in 1+3 covariant and 1+3
orthonormal frame notation, and show there exists a series of constraint
equations that need to be satisfied. These conditions hold identically for
FLRW-linearised silent models, but not in the general exact non-linear case.
Thus there is a linearisation instability, and it is highly unlikely that there
is a large class of silent models. We conjecture that there are no spatially
inhomogeneous solutions with Weyl curvature of Petrov type I, and indicate
further issues that await clarification.Comment: Minor corrections and improvements; 1 new reference; to appear Class.
Quantum Grav.; 16 pages Ioplpp
Anomaly-Free Gauged R-Symmetry
We review the gauging of an R-symmetry in local and global susy. We then
construct the first anomaly-free models. We break the R-symmetry and susy at
the Planck scale and discuss the low-energy effects. We include a solution to
the mu-problem, and the prediction of observable effects at HERA. The models
also nicely allow for GUT-scale baryogenesis and R-parity violation without the
sphaleron interactions erasing the baryon-asymmetry.Comment: 6 pages, latex, no figures. Talk presented at SUSY-95. Work done in
collaboration with A. Chamseddin
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