1,596 research outputs found
Light and Life: Exotic Photosynthesis in Binary Star Systems
The potential for hosting photosynthetic life on Earth-like planets within
binary/multiple stellar systems was evaluated by modelling the levels of
photosynthetically active radiation (PAR) such planets receive. Combinations of
M and G stars in: (i) close-binary systems; (ii) wide-binary systems and (iii)
three-star systems were investigated and a range of stable radiation
environments found to be possible. These environmental conditions allow for the
possibility of familiar, but also more exotic forms of photosynthetic life,
such as infrared photosynthesisers and organisms specialised for specific
spectral niches.Comment: Accepted for publication in: Astrobiolog
Cosmological Effects of Radion Oscillations
We show that the redshift of pressureless matter density due to the expansion
of the universe generically induces small oscillations in the stabilized radius
of extra dimensions (the radion field). The frequency of these oscillations is
proportional to the mass of the radion and can have interesting cosmological
consequences. For very low radion masses () these low frequency oscillations lead to oscillations in
the expansion rate of the universe. The occurrence of acceleration periods
could naturally lead to a resolution of the coincidence problem, without need
of dark energy. Even though this scenario for low radion mass is consistent
with several observational tests it has difficulty to meet fifth force
constraints. If viewed as an effective Brans-Dicke theory it predicts
( is the number of extra dimensions), while
experiments on scales larger than imply . By deriving the
generalized Newtonian potential corresponding to a massive toroidally compact
radion we demonstrate that Newtonian gravity is modified only on scales smaller
than . Thus, these constraints do not apply for
(high frequency oscillations) corresponding to scales less than the current
experiments (). Even though these high frequency oscillations can not
resolve the coincidence problem they provide a natural mechanism for dark
matter generation. This type of dark matter has many similarities with the
axion.Comment: Accepted in Phys. Rev. D. Clarifying comments added in the text and
some additional references include
Supergravity Inflation on the Brane
We study N=1 Supergravity inflation in the context of the braneworld
scenario. Particular attention is paid to the problem of the onset of inflation
at sub-Planckian field values and the ensued inflationary observables. We find
that the so-called -problem encountered in supergravity inspired
inflationary models can be solved in the context of the braneworld scenario,
for some range of the parameters involved. Furthermore, we obtain an upper
bound on the scale of the fifth dimension, M_5 \lsim 10^{-3} M_P, in case the
inflationary potential is quadratic in the inflaton field, . If the
inflationary potential is cubic in , consistency with observational data
requires that .Comment: 6 pages, 1 figure, to appear in Phys. Rev.
Large lepton asymmetry from Q-balls
We propose a scenario which can explain large lepton asymmetry and small
baryon asymmetry simultaneously. Large lepton asymmetry is generated through
Affleck-Dine (AD) mechanism and almost all the produced lepton numbers are
absorbed into Q-balls (L-balls). If the lifetime of the L-balls is longer than
the onset of electroweak phase transition but shorter than the epoch of big
bang nucleosynthesis (BBN), the large lepton asymmetry in the L-balls is
protected from sphaleron effects. On the other hand, small (negative) lepton
numbers are evaporated from the L-balls due to thermal effects, which are
converted into the observed small baryon asymmetry by virtue of sphaleron
effects. Large and positive lepton asymmetry of electron type is often
requested from BBN. In our scenario, choosing an appropriate flat direction in
the minimal supersymmetric standard model (MSSM), we can produce positive
lepton asymmetry of electron type but totally negative lepton asymmetry.Comment: 10 pages, 3 figures, ReVTeX
Scalar Dark Matter From Theory Space
The scalar dark matter candidate in a prototypical theory space little Higgs
model is investigated. We review all details of the model pertinent to dark
matter. We perform a thermal relic density calculation including couplings to
the gauge and Higgs sectors of the model. We find two regions of parameter
space that give acceptable dark matter abundances. The first region has a dark
matter candidate with a mass of order 100 GeV, the second region has a heavy
candidate with a mass greater than about 500 GeV$. The dark matter candidate in
either region is an admixture of an SU(2) triplet and an SU(2) singlet, thereby
constituting a WIMP (weakly interacting massive particle).Comment: 18 pages, 2 figures, version to appear in PR
Expression of mucin synthesis and secretion in human tracheobronchial epithelial cells grown in culture.
The effects of culture conditions on growth and differentiation of human tracheobronchial epithelial (HTBE) cells have been defined. Epithelial cells were dissociated from tissues by protease treatment and were plated on tissue culture dishes in F12 medium supplemented with insulin, transferrin, epidermal growth factor, hydrocortisone, cholera toxin, bovine hypothalamus extract, and retinol. HTBE cells did not express any mucociliary function (ciliogenesis or mucin secretion) on tissue culture plastic, but they could be passaged 3 to 5 times with a total of 10 to 25 population doublings. Cells from early passages re-express both these functions when transplanted to tracheal grafts. When tissue culture plates were coated with collagen film or collagen gel substrata, cell attachment and proliferation were stimulated. However, the expression of mucous cell function in culture occurred only when cells were plated on collagen gel substrata and vitamin A (retinol) was present in the medium. Mucous cell differentiation under optimal conditions was defined by ultrastructural studies, by immunologic studies with mucin-specific monoclonal antibodies, and by carbohydrate and amino acid compositional analyses of mucin-like glycoproteins purified from culture medium. These results demonstrate for the first time that HTBE cells can express mucin synthesis and secretion under appropriate culture conditions
A Hedged Monte Carlo Approach to Real Option Pricing
In this work we are concerned with valuing optionalities associated to invest
or to delay investment in a project when the available information provided to
the manager comes from simulated data of cash flows under historical (or
subjective) measure in a possibly incomplete market. Our approach is suitable
also to incorporating subjective views from management or market experts and to
stochastic investment costs. It is based on the Hedged Monte Carlo strategy
proposed by Potters et al (2001) where options are priced simultaneously with
the determination of the corresponding hedging. The approach is particularly
well-suited to the evaluation of commodity related projects whereby the
availability of pricing formulae is very rare, the scenario simulations are
usually available only in the historical measure, and the cash flows can be
highly nonlinear functions of the prices.Comment: 25 pages, 14 figure
Distribution function approach to redshift space distortions. Part II: N-body simulations
Measurement of redshift-space distortions (RSD) offers an attractive method
to directly probe the cosmic growth history of density perturbations. A
distribution function approach where RSD can be written as a sum over density
weighted velocity moment correlators has recently been developed. We use Nbody
simulations to investigate the individual contributions and convergence of this
expansion for dark matter. If the series is expanded as a function of powers of
mu, cosine of the angle between the Fourier mode and line of sight, there are a
finite number of terms contributing at each order. We present these terms and
investigate their contribution to the total as a function of wavevector k. For
mu^2 the correlation between density and momentum dominates on large scales.
Higher order corrections, which act as a Finger-of-God (FoG) term, contribute
1% at k~0.015h/Mpc, 10% at k~0.05h/Mpc at z=0, while for k>0.15h/Mpc they
dominate and make the total negative. These higher order terms are dominated by
density-energy density correlations which contribute negatively to the power,
while the contribution from vorticity part of momentum density auto-correlation
is an order of magnitude lower. For mu^4 term the dominant term on large scales
is the scalar part of momentum density auto-correlation, while higher order
terms dominate for k>0.15h/Mpc. For mu^6 and mu^8 we find it has very little
power for k<0.15h/Mpc. We also compare the expansion to the full 2D P^ss(k,mu)
as well as to their multipoles. For these statistics an infinite number of
terms contribute and we find that the expansion achieves percent level accuracy
for kmu<0.15h/Mpc at 6th order, but breaks down on smaller scales because the
series is no longer perturbative. We explore resummation of the terms into FoG
kernels, which extend the convergence up to a factor of 2 in scale. We find
that the FoG kernels are approximately Lorentzian.Comment: 21 pages, 9 figures, published in JCA
Large and Almost Maximal Neutrino Mixing within the Type II See-Saw Mechanism
Within the type II see-saw mechanism the light neutrino mass matrix is given
by a sum of a direct (or triplet) mass term and the conventional (type I)
see-saw term. Both versions of the see-saw mechanism explain naturally small
neutrino masses, but the type II scenario offers interesting additional
possibilities to explain large or almost maximal or vanishing mixings which are
discussed in this paper. We first introduce ``type II enhancement'' of neutrino
mixing, where moderate cancellations between the two terms can lead to large
neutrino mixing even if all individual mass matrices and terms generate small
mixing. However, nearly maximal or vanishing mixings are not naturally
explained in this way, unless there is a certain initial structure (symmetry)
which enforces certain elements of the matrices to be identical or related in a
special way. We therefore assume that the leading structure of the neutrino
mass matrix is the triplet term and corresponds to zero U_{e3} and maximal
theta_{23}. Small but necessary corrections are generated by the conventional
see-saw term. Then we assume that one of the two terms corresponds to an
extreme mixing scenario, such as bimaximal or tri-bimaximal mixing. Deviations
from this scheme are introduced by the second term. One can mimic Quark-Lepton
Complementarity in this way. Finally, we note that the neutrino mass matrix for
tri-bimaximal mixing can be -- depending on the mass hierarchy -- written as a
sum of two terms with simple structure. Their origin could be the two terms of
type II see-saw.Comment: 25 pages. Comments and references added, to appear in JHE
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