3 research outputs found
Addressing \mu-b_\mu and proton lifetime problems and active neutrino masses in a U(1)^\prime-extended supergravity model
We present a locally supersymmetric extension of the minimal supersymmetric
Standard Model (MSSM) based on the gauge group where, except for the supersymmetry breaking scale
which is fixed to be GeV, we require that all non-Standard-Model
parameters allowed by the {\it local} spacetime and gauge symmetries assume
their natural values. The symmetry, which is spontaneously broken
at the intermediate scale, serves to ({\it i}) explain the weak scale
magnitudes of and terms, ({\it ii}) ensure that dimension-3 and
dimension-4 baryon-number-violating superpotential operators are forbidden,
solving the proton-lifetime problem, ({\it iii}) predict {\it bilinear lepton
number violation} in the superpotential at just the right level to accommodate
the observed mass and mixing pattern of active neutrinos (leading to a novel
connection between the SUSY breaking scale and neutrino masses), while
corresponding trilinear operators are strongly supppressed. The phenomenology
is like that of the MSSM with bilinear R-parity violation, were the would-be
lightest supersymmetric particle decays leptonically with a lifetime of s. Theoretical consistency of our model requires the
existence of multi-TeV, stable, colour-triplet, weak-isosinglet scalars or
fermions, with either conventional or exotic electric charge which should be
readily detectable if they are within the kinematic reach of a hadron collider.
Null results of searches for heavy exotic isotopes implies that the re-heating
temperature of our Universe must have been below their mass scale which, in
turn, suggests that sphalerons play a key role for baryogensis. Finally, the
dark matter cannot be the weakly interacting neutralino.Comment: 33 pages, 2 figures, Discussion on proton decay and radiative
neutrino masses augmented, and references adde
When do colliding bubbles produce an expanding universe?
It is intriguing to consider the possibility that the Big Bang of the
standard (3+1) dimensional cosmology originated from the collision of two
branes within a higher dimensional spacetime, leading to the production of a
large amount of entropy. In this paper we study, subject to certain
well-defined assumptions, under what conditions such a collision leads to an
expanding universe. We assume the absence of novel physics, so that ordinary
(4+1) -dimensional Einstein gravity remains a valid approximation. It is
necessary that the fifth dimension not become degenerate at the moment of
collision. First the case of a symmetric collision of infinitely thin branes
having a hyperbolic or flat spatial geometry is considered. We find that a
symmetric collision results in a collapsing universe on the final brane unless
the pre-existing expansion rate in the bulk just prior to the collision is
sufficiently large in comparison to the momentum transfer in the fifth
dimension. Such prior expansion may either result from negative spatial
curvature or from a positive five-dimensional cosmological constant. The
relevance of these findings to the Colliding Bubble Braneworld Universe
scenario is discussed. Finally, results from a numerical study of colliding
thick-wall branes is presented, which confirm the results of the thin-wall
approximation.Comment: 24 pages, 13 figures. Minor changes and references include
Cosmological Perturbations Generated in the Colliding Bubble Braneworld Universe
We compute the cosmological perturbations generated in the colliding bubble
braneworld universe in which bubbles filled with five-dimensional anti-de
Sitter space (AdS5)expanding within a five dimensional de Sitter space (dS5) or
Minkowski space (M5) collide to form a (3+1) dimensional local brane on which
the cosmology is virtually identical to that of the Randall-Sundrum model. The
perturbation calculation presented here is valid to linear order but treats the
fluctuations of the expanding bubbles as (3+1) dimensional fields localized on
the bubble wall. We find that for bubbles expanding in dS5 the dominant
contribution to the power spectrum is `red' but very small except in certain
cases where the fifth dimension is not large or the bubbles have expanded to
far beyond the dS5 apparent horizon length. This paper supersedes a previous
version titled "Exactly Scale-Invariant Cosmological Perturbations From a
Colliding Bubble Braneworld Universe" in which we erroneously claimed that a
scale-invariant spectrum results for the case of bubbles expanding in M5. This
present paper corrects the errors of the previous version and extends the
analysis to the more interesting and general case of bubbles expanding in dS5.Comment: 29 pages Latex with eps figures. Major errors in the original version
of the paper corrected and analysis extended to bubbles expanding in dS