63 research outputs found
Hybrid Inflation, Dark Energy And Dark Matter
It has been suggested that the dark energy density \rho_v ~ 10^{-12} eV^4 in
the universe is associated with a metastable (false) vacuum, while the true
vacuum has a vanishing cosmological constant. By including supergravity
corrections we show how this is naturally realized in realistic supersymmetric
hybrid inflation models. With a fundamental supersymmetry breaking scale ~ TeV,
the LSP is not a suitable candidate for cold dark matter. We consider axion
physics to overcome this and simultaneously provide a resolution of the MSSM
\mu problem.Comment: 11 pages, no figure
New Mechanisms for Transmission of Supersymmetry Breaking
We considered new mechanisms for transmission of supersymmetry breaking and their phenomenological consequences. Specifically, we investigated the scalar mass corrections via five-dimensional supergravity loops and explored the possibility that supersymmetry is an accidental symmetry of Nature. We find that both these lead to phenomenologically viable scenarios. In the former, the negative slepton mass-squared masses arising from minimal anomaly mediation is cured. In the latter, which constitutes a paradigm shift, we find a more natural framework for low-energy supersymmetry than the conventional picture
Reactor Searches for Neutrino Magnetic Moment as a Probe of Extra Dimensions
We present calculations of the magnetic moment contribution to neutrino
electron scattering in large extra dimension brane-bulk models (LED) with three
bulk neutrinos. We discuss the cases with two and three large extra dimensions
of sizes . The calculations are done using reactor flux from Uranium,
as the neutrino source. We find that if the electron neutrino mass is
chosen to be in the range of one eV, the differential cross section for
scattering for low electron recoil energy can be of the same
order as the presently explored values in reactor experiments. Furthermore the
spectral shape for the LED models is different from the four dimensional case.
Future higher precision reactor experiments can therefore be used to provide
new constraints on a class of large extra dimension theories.Comment: 8 pages; 3 figure
Minimal SUSY SO(10), b- unification and large neutrino mixings
We show that the assumption of type II seesaw mechanism for small neutrino
masses coupled with mass unification in a minimal SUSY SO(10) model
leads not only to a natural understanding of large atmospheric mixing angle
() among neutrinos, as recently pointed out, but also to large
solar angle () and a small as required
to fit observations. This is therefore a minimal, completely realistic grand
unified model for all low energy observations that naturally explains the
diverse mixing patterns between the quark and leptons without any additional
inputs such as extra global symmetries. The proposed long baseline neutrino
experiments will provide a crucial test of this model since it predicts
for the allowed range of parameters.Comment: 15 pages, latex, 3 figures, UMD-PP-03-03
Ghost Cosmology: Exact Solutions, Transitions Between Standard Cosmologies and Ghost Dark Energy/Matter Evolution
The recently proposed infrared modification of gravity through the
introduction of a ghost scalar field results in a number of interesting
cosmological and phenomenological implications. In this paper, we derive the
exact cosmological solutions for a number of scenarios where at late stages,
the ghost behaves like dark matter, or dark energy. The full solutions give
valuable information about the non-linear regime beyond the asymptotic first
order analysis presented in the literature. The generic feature is that these
ghost cosmologies give rise to smooth transitions between radiation dominated
phases (or more general power-law expansions) at early epochs and ghost dark
matter resp. ghost dark energy dominated late epochs. The current age of our
universe places us right at the non-linear transition phase. By studying the
evolution backwards in time, we find that the dominance of the ghost over
ordinary baryonic matter and radiative contributions persists back to the
earliest times such that the Friedmann-Robertson-Walker geometry is dictated to
a good approximation by the ghost alone. We also find that the Jeans
instability occurs in the ghost dark energy scenario at late times, while it is
absent in the ghost dark matter scenario.Comment: 31 pages, 9 figures; added references, clarified a few minor point
Enhancement of Power Output by using Alginate Immobilized Algae in Biophotovoltaic Devices.
We report for the first time a photosynthetically active algae immobilized in alginate gel within a fuel cell design for generation of bioelectricity. The algal-alginate biofilm was utilized within a biophotovoltaics (BPV) device developed for direct bioelectricity generation from photosynthesis. A peak power output of 0.289 mWm-2 with an increase of 18% in power output compared to conventional suspension culture BPV device was observed. The increase in maximum power density was correlated to the maximum relative electron transport rate (rETRm). The semi-dry type of photosynthetically active biofilm proposed in this work may offer significantly improved performances in terms of fuel cell design, bioelectricity generation, oxygen production and CO2 reduction
Dark Matter in Gauge Mediation from Emergent Supersymmetry
We investigated the viability of neutralino dark matter in the gauge
mediation from emergent supersymmetry proposal. In this proposal, supersymmetry
is broken at Planck scale and consequently, the gravitino is superheavy and
completely decouples from the low energy theory. Squarks and sleptons obtain
their soft masses dominantly through gauge mediation with other mechanisms
highly suppressed. The lightest supersymmetric partner, in contrast to
traditional gauge mediation, is a neutralino which is also a dark matter
candidate. By explicit calculation of the low energy spectra, the parameter
space was constrained using the WMAP observed relic density of dark matter,
LEP2 Higgs mass bounds, collider bounds on supersymmetric partners and exotic
B-meson decays. We found that the model has intriguing hybrid features such as
a nearly gauge-mediated spectrum (the exception being the superheavy gravitino)
but with a dominant mSUGRA-like bino-stau coannihilation channel and at large
, A-resonance-like annihilation.Comment: 14 pages, 4 figure
Genetic and morphological analyses of Gracilaria firma and G. changii (Gracilariaceae, Rhodophyta), the commercially important agarophytes in western Pacific
Many studies classifying Gracilaria species for the exploitation of agarophytes and the development of the agar industry were conducted before the prevalence of molecular tools, resulting in the description of many species based solely on their morphology. Gracilaria firma and
G. changii are among the commercially important agarophytes from the western Pacific; both feature branches with basal constrictions that taper toward acute apices. In this study, we contrasted the morpho-anatomical circumscriptions of the two traditionally described species with molecular data from samples that included representatives of G. changii collected from its type locality. Concerted molecular analyses using the rbcL and cox1 gene sequences,
coupled with morphological observations of the collections from the western Pacific, revealed no inherent differences to support the treatment of the two entities as distinct taxa. We propose merging G. changii (a later synonym) into G. firma and recognize G. firma based on
thallus branches with abrupt basal constrictions that gradually taper toward acute (or sometimes broken) apices, cystocarps consisting of small gonimoblast cells and inconspicuous multinucleate tubular nutritive cells issuing from gonimoblasts extending into the inner pericarp
at the cystocarp floor, as well as deep spermatangial conceptacles of the verrucosatype. The validation of specimens under different names as a single genetic species is useful to allow communication and knowledge transfer among groups from different fields. This study also revealed considerably low number of haplotypes and nucleotide diversity with apparent phylogeographic patterns for G. firma in the region. Populations from the Philippines
and Taiwan were divergent from each other as well as from the populations from Malaysia, Thailand, Singapore and Vietnam. Establishment of baseline data on the genetic
diversity of this commercially important agarophyte is relevant in the context of cultivation, as limited genetic diversity may jeopardize the potential for its genetic improvement over time
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