1,742 research outputs found
Constraints on Deflation from the Equation of State of Dark Energy
In cyclic cosmology based on phantom dark energy the requirement that our
universe satisfy a CBE-condition ({\it Comes Back Empty}) imposes a lower bound
on the number of causal patches which separate just prior to
turnaround. This bound depends on the dark energy equation of state with . More accurate measurement of will
constrain . The critical density in the model has a lower
bound or
when the smallest bound state has size m, or m,
respectively.Comment: 23 pages, 3 figures, typos fixe
Minimal Family Unification
Absract It is proposed that there exist, within a new , a gauged
discrete group (the order 12 double dihedral group) acting as a family
symmetry. This nonabelian finite group can explain hierarchical features of
families, using an assignment for quarks and leptons dictated by the
requirements of anomaly cancellation and of no additional quarks.Comment: 10 pages, IFP-701-UNC;VAND-TH-94-
Upper and Lower Bounds on Gravitational Entropy
The entropy in the interior of the Universe has many contributions including
well understood ones from radiation and relic neutrinos. The gravitational
entropy is larger and more subtle. One contribution which provides our lower
bound is from supermassive black holes at the centers of galaxies. The
remainder is harder to pin down. We suggest an upper bound which is many orders
of magnitude below the holographic bound yet above that of the supermassive
black holes. We propose that gravitational entropy in dark matter halos is the
largest contributor to the present entropy of the universe.Comment: 10 pages LaTeX. Minor correction
Possible manifestation of heavy stable colored particles in cosmology and cosmic rays
We discuss the cosmological implications as well as possible observability of
massive, stable, colored particles which often appear in the discussion of
physics beyond the standard model. We argue that if their masses are more than
a few hundred GeV and if they saturate the halo density and/or occur with
closure density of the universe, they are ruled out by the present WIMP search
experiments as well as the searches for anomalous heavy isotopes of ordinary
nuclei. We then comment on the possibility that these particles as well as the
monopoles could be responsible for the ultra high energy cosmic rays with
energy eV and point out that their low inelasticity argues
against this.Comment: 9 pages; UMD-PP-98-1
Echoes of the fifth dimension?
In this article we examine the question of whether the highest energy cosmic
ray primaries could be ultra relativistic magnetic monopoles. The analysis is
performed within the framework of large compact dimensions and TeV scale
quantum gravity. Our study indicates that while this hypothesis must be
regarded as highly speculative it cannot be ruled out with present data.Comment: Revised version accepted for publication in Physical Review D. The
bibliography has been considerably reduced for the journal version due to
limited spac
Muon anomalous magnetic moment in string inspired extended family models
We propose a standard model minimal extension with two lepton weak SU(2)
doublets and a scalar singlet to explain the deviation of the measured
anomalous magnetic moment of the muon from the standard model expectation. This
scheme can be naturally motivated in string inspired models such as E_6 and
AdS/CFT.Comment: 9 pages, RevTeX, 2 figures, version to be published in Phys. Rev.
High-Energy Tests of Lorentz Invariance
We develop a perturbative framework with which to discuss departures from
exact Lorentz invariance and explore their potentially observable
ramifications. Tiny non-invariant terms introduced into the standard model
Lagrangian are assumed to be renormalizable (dimension ), invariant
under gauge transformations, and rotationally
and translationally invariant in a preferred frame. There are a total of 46
independent TCP-even perturbations of this kind, all of which preserve anomaly
cancellation. They define the energy-momentum eigenstates and their maximal
attainable velocities in the high-energy limit. The effects of these
perturbations increase rapidly with energy in the preferred frame, more rapidly
than those of TCP-odd perturbations. Our analysis of Lorentz-violating
kinematics reveals several striking new phenomena that are relevant both to
cosmic-ray physics ({\it e.g.,} by undoing the GZK cutoff) and neutrino physics
({\it e.g.,} by generating novel types of neutrino oscillations). These may
lead to new and sensitive high-energy tests of special relativity.Comment: 33 pages, uses harvmac. This 2nd revision corrects two typos, an
error in the Appendix, and includes further acknowledgement
Quantum Gravity, the Origin of Time and Time's Arrow
The local Lorentz and diffeomorphism symmetries of Einstein's gravitational
theory are spontaneously broken by a Higgs mechanism by invoking a phase
transition in the early Universe, at a critical temperature below which
the symmetry is restored. The spontaneous breakdown of the vacuum state
generates an external time and the wave function of the Universe satisfies a
time dependent Schrodinger equation, which reduces to the Wheeler-deWitt
equation in the classical regime for , allowing a semi-classical WKB
approximation to the wave function. The conservation of energy is spontaneously
violated for and matter is created fractions of seconds after the big
bang, generating the matter in the Universe. The time direction of the vacuum
expectation value of the scalar Higgs field generates a time asymmetry, which
defines the cosmological arrow of time and the direction of increasing entropy
as the Lorentz symmetry is restored at low temperatures.Comment: 37 page
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