298 research outputs found
Out of equilibrium: understanding cosmological evolution to lower-entropy states
Despite the importance of the Second Law of Thermodynamics, it is not
absolute. Statistical mechanics implies that, given sufficient time, systems
near equilibrium will spontaneously fluctuate into lower-entropy states,
locally reversing the thermodynamic arrow of time. We study the time
development of such fluctuations, especially the very large fluctuations
relevant to cosmology. Under fairly general assumptions, the most likely
history of a fluctuation out of equilibrium is simply the CPT conjugate of the
most likely way a system relaxes back to equilibrium. We use this idea to
elucidate the spacetime structure of various fluctuations in (stable and
metastable) de Sitter space and thermal anti-de Sitter space.Comment: 27 pages, 11 figure
Family Symmetry, Gravity, and the Strong CP Problem
We show how in a class of models Peccei--Quinn symmetry can be realized as an
automatic consequence of a gauged family symmetry. These models provide
a solution to the strong CP problem either via a massless --quark or via the
DFSZ invisible axion. The local family symmetry protects against potentially
large corrections to induced by quantum gravitational
effects. In a supersymmetric extension, the `--problem' is shown to have a
natural solution in the context of gravitationally induced operators. We also
present a plausible mechanism which can explain the inter--generational mass
hierarchy in such a context.Comment: BA-92-79, 14 pages, in LaTeX, no figure
Visible Sector Supersymmetry Breaking Revisited
We revisit the possibility of "visible sector" SUSY models: models which are
straightforward renormalizable extensions of the Minimal Supersymmetric
Standard Model (MSSM), where SUSY is broken at tree level. Models of this type
were abandoned twenty years ago due to phenomenological problems, which we
review. We then demonstrate that it is possible to construct simple
phenomenologically viable visible sector SUSY models. Such models are indeed
very constrained, and have some inelegant features. They also have interesting
and distinctive phenomenology. Our models predict light gauginos and very heavy
squarks and sleptons. The squarks and sleptons may not be observable at the
LHC. The LSP is a stable very light gravitino with a significant Higgsino
admixture. The NLSP is mostly Bino. The Higgs boson is naturally heavy. Proton
decay is sufficently and naturally suppressed, even for a cutoff scale as low
as 10^8 GeV. The lightest particle of the O'Raifeartaigh sector (the LOP) is
stable, and is an interesting cold dark matter candidate.Comment: 23 pages, 3 figures, LaTe
Product Groups, Discrete Symmetries, and Grand Unification
We study grand unified theories based on an SU(5)xSU(5) gauge group in which
the GUT scale, M_{GUT}, is the VEV of an exact or approximate modulus, and in
which fast proton decay is avoided through a combination of a large triplet
mass and small triplet couplings. These features are achieved by discrete
symmetries. In many of our models, M_{GUT} is generated naturally by the
balance of higher dimension terms that lift the GUT modulus potential, and soft
supersymmetry breaking masses. The theories often lead to interesting patterns
of quark and lepton masses. We also discuss some distinctions between grand
unified theories and string unification.Comment: 23 pages; no figures; revtex
Supernovae as a probe of particle physics and cosmology
It has very recently been demonstrated by Csaki, Kaloper and Terning (CKT)
that the faintness of supernovae at high redshift can be accommodated by mixing
of a light axion with the photon in the presence of an intergalactic magnetic
field, as opposed to the usual explanation of an accelerating universe by a
dark energy component. In this paper we analyze further aspects of the CKT
mechanism and its generalizations. The CKT mechanism also passes various
cosmological constraints from the fluctuations of the CMB and the formation of
structure at large scales, without requiring an accelerating phase in the
expansion of the Universe. We investigate the statistical significance of
current supernova data for pinning down the different components of the
cosmological energy-momentum tensor and for probing physics beyond the standard
models.Comment: 17 pages, LaTeX, 4 figures; v2: typos corrected, minor changes,
references added; v3: updated figures, details regarding fits include
Domain walls between gauge theories
Noncommutative U(N) gauge theories at different N may be often thought of as
different sectors of a single theory: the U(1) theory possesses a sequence of
vacua labeled by an integer parameter N, and the theory in the vicinity of the
N-th vacuum coincides with the U(N) noncommutative gauge theory. We construct
noncommutative domain walls on fuzzy cylinder, separating vacua with different
gauge theories. These domain walls are solutions of BPS equations in gauge
theory with an extra term stabilizing the radius of the cylinder. We study
properties of the domain walls using adjoint scalar and fundamental fermion
fields as probes. We show that the regions on different sides of the wall are
not disjoint even in the low energy regime -- there are modes penetrating from
one region to the other. We find that the wall supports a chiral fermion zero
mode. Also, we study non-BPS solution representing a wall and an antiwall, and
show that this solution is unstable. We suggest that the domain walls emerge as
solutions of matrix model in large class of pp-wave backgrounds with
inhomogeneous field strength. In the M-theory language, the domain walls have
an interpretation of a stack of branes of fingerstall shape inserted into a
stack of cylindrical branes.Comment: Final version; minor corrections; to appear in Nucl.Phys.
Polarized Proton Scattering at 134 MeV from 154-Sm and 166-Er
This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit
The 13-C(p,d) Reaction at 120 MeV
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Cosmological Constant of the -Dimensional World, Embedded in the -Dimensional Bulk Space
In this manuscript we study the cosmological constant of a
-dimensional world, which lives in the higher dimensional bulk space. We
assume the extra dimensions are compact on tori. We consider two cases:
positive and negative bulk cosmological constant. It is pointed out that the
tiny cosmological constant of our world can be obtained by the dynamics of a
scalar field and adjusting the parameters of the model. The cosmological
constant of the dual world also will be discussed. We obtain the Dirac
quantization of these cosmological constants.Comment: 11 pages, Latex, No figure. In the revised version, major changes
have been introduced and also references have been adde
Conservation Laws and 2D Black Holes in Dilaton Gravity
A very general class of Lagrangians which couple scalar fields to gravitation
and matter in two spacetime dimensions is investigated. It is shown that a
vector field exists along whose flow lines the stress-energy tensor is
conserved, regardless of whether or not the equations of motion are satisfied
or if any Killing vectors exist. Conditions necessary for the existence of
Killing vectors are derived. A new set of 2D black hole solutions is obtained
for one particular member within this class of Lagrangians. One such solution
bears an interesting resemblance to the 2D string-theoretic black hole, yet
contains markedly different thermodynamic properties.Comment: 11 pgs. WATPHYS-TH92/0
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