432 research outputs found
Supersymmetry, Axions and Cosmology
Various authors have noted that in particular models, the upper bound on the
axion decay constant may not hold. We point out that within supersymmetry, this
is a generic issue. For large decay constants, the cosmological problems
associated with the axion's scalar partner are far more severe than those of
the axion. We survey a variety of models, both for the axion multiplet and for
cosmology, and find that in many cases where the cosmological problems of the
saxion are solved, the usual upper bound on the axion is significantly relaxed.
We discuss, more generally, the cosmological issues raised by the pseudoscalar
members of moduli multiplets, and find that they are potentially quite severe.Comment: 27 pages, published version, some discussions clarifie
Superficial geology and hydrogeological domains between Durham and Darlington. Phase 1, (Durham South)
The North East Region’s Groundwater Modelling Strategy has identified the need for the
development of a conceptual model for the Magnesian Limestone aquifer. In line with the
Environment Agency R&D Technical Report W214 (Environment Agency Framework for
Groundwater Resources Conceptual and Numerical Modelling), a scoping study was produced,
that identified areas of uncertainty and work required for the development of the conceptual
model.
The purpose of this project is to give the Environment Agency (EA) a regional understanding of
the geology and hydrogeology of the Magnesian Limestone and overlying superficial deposits in
the North East Region, using information presently held by the British Geological Survey (BGS).
This report contributes to the conceptual model and understanding of the Magnesian Limestone
aquifer.
There is uncertainty in the amount of recharge that the Magnesian Limestone receives from
rainfall. The project is designed to gain a greater understanding of the geology of the superficial
deposits and their hydrogeological properties. These are the key factors for the calculation of
recharge to the Magnesian Limestone aquifer from rainfall. This element of the conceptual
model is essential in understanding the potential water resource available within this aquifer
Superficial geology and hydrogeological domains between Durham and Darlington. Phase 2, (Durham North)
The North East Region’s Groundwater Modelling Strategy has identified the need for the
development of a conceptual model for the Magnesian Limestone aquifer. In line with the
Environment Agency R&D Technical Report W214 (Environment Agency Framework for
Groundwater Resources Conceptual and Numerical Modelling), a scoping study was produced,
that identified areas of uncertainty and work required for the development of the conceptual
model.
The purpose of this project is to give the Environment Agency (EA) a regional understanding of
the geology and hydrogeology of the Magnesian Limestone and overlying superficial deposits in
the North East Region, using information held by the British Geological Survey (BGS). This
report contributes to the conceptual model and understanding of the Magnesian Limestone
aquifer.
There is uncertainty in the amount of recharge that the Magnesian Limestone receives from
rainfall. The project is designed to gain a greater understanding of the geology of the superficial
deposits and their hydrogeological properties. These are the key factors for the calculation of
recharge to the Magnesian Limestone aquifer from rainfall. This element of the conceptual
model is essential in understanding the potential water resource available within this aquifer
Inflationary cosmology in the central region of String/M-theory moduli space
The "central" region of moduli space of M- and string theories is where the
string coupling is about unity and the volume of compact dimensions is about
the string volume. Here we argue that in this region the non-perturbative
potential which is suggested by membrane instanton effects has the correct
scaling and shape to allow for enough slow-roll inflation, and to produce the
correct amplitude of CMB anisotropies. Thus, the well known theoretical
obstacles for achieving viable slow-roll inflation in the framework of
perturbative string theory are overcome. Limited knowledge of some generic
properties of the induced potential is sufficient to determine the simplest
type of consistent inflationary model and its predictions about the spectrum of
cosmic microwave background anisotropies: a red spectrum of scalar
perturbations, and negligible amount of tensor perturbations.Comment: 9 pages, 1 figur
Natural Warm Inflation
We derive the requirements that a generic axion-like field has to satisfy in
order to play the role of the inflaton field in the warm inflation scenario.
Compared to the parameter space in ordinary natural inflation models, we find
that the parameter space in our model is enlarged. In particular, we avoid the
problem of having an axion decay constant that relates to the Planck scale,
which is instead present in the ordinary natural inflation models; in fact, our
model can easily accommodate values of the axion decay constant that lie well
below the Planck scale.Comment: 19 pages, 7 figures; version accepted in JCA
From Big Crunch to Big Bang
We consider conditions under which a universe contracting towards a big
crunch can make a transition to an expanding big bang universe. A promising
example is 11-dimensional M-theory in which the eleventh dimension collapses,
bounces, and re-expands. At the bounce, the model can reduce to a weakly
coupled heterotic string theory and, we conjecture, it may be possible to
follow the transition from contraction to expansion. The possibility opens the
door to new classes of cosmological models. For example, we discuss how it
suggests a major simplification and modification of the recently proposed
ekpyrotic scenario.Comment: 16 pages, compressed and RevTex file, including three postscript
figure files. Minor changes, version to appear in Physical Review
Suppressing the and neutrino masses by a superconformal force
The idea of Nelson and Strassler to obtain a power law suppression of
parameters by a superconformal force is applied to understand the smallness of
the parameter and neutrino masses in R-parity violating supersymmetric
standard models. We find that the low-energy sector should contain at least
another pair of Higgs doublets, and that a suppression of \lsim O(10^{-13})
for the parameter and neutrino masses can be achieved generically. The
superpotential of the low-energy sector happens to possess an anomaly-free
discrete R-symmetry, either or , which naturally suppresses certain
lepton-flavor violating processes, the neutrinoless double beta decays and also
the electron electric dipole moment. We expect that the escape energy of the
superconformal sector is \lsim O(10) TeV so that this sector will be
observable at LHC. Our models can accommodate to a large mixing among neutrinos
and give the same upper bound of the lightest Higgs mass as the minimal
supersymmetric standard model.Comment: 24 page
Mutated Hilltop Inflation : A Natural Choice for Early Universe
We propose a model of inflation with a suitable potential for a single scalar
field which falls in the wide class of hilltop inflation. We derive the
analytical expressions for most of the physical quantities related to inflation
and show that all of them represent the true behavior as required from a model
of inflation. We further subject the results to observational verification by
formulating the theory of perturbations based on our model followed by an
estimation for the values of those observable parameters. Our model is found to
be in excellent agreement with observational data. Thus, the features related
to the model leads us to infer that this type of hilltop inflation may be a
natural choice for explaining the early universe.Comment: 22 pages, 7 figures, 2 tables. Matches published version in JCA
Relating the Cosmological Constant and Supersymmetry Breaking in Warped Compactifications of IIB String Theory
It has been suggested that the observed value of the cosmological constant is
related to the supersymmetry breaking scale M_{susy} through the formula Lambda
\sim M_p^4 (M_{susy}/M_p)^8. We point out that a similar relation naturally
arises in the codimension two solutions of warped space-time varying
compactifications of string theory in which non-isotropic stringy moduli induce
a small but positive cosmological constant.Comment: 7 pages, LaTeX, references added and minor changes made, (v3) map
between deSitter and global cosmic brane solutions clarified, supersymmetry
breaking discussion improved and references adde
Gauge coupling unification with large extra dimensions
We make a detailed study of the unification of gauge couplings in the MSSM
with large extra dimensions. We find some scenarios where unification can be
achieved (with the strong coupling constant at the Z mass within one standard
deviation of the experimental value) with both the compactification scale and
the SUSY breaking scale in the few TeV range. No enlargement of the gauge group
or particle content is needed. One particularly interesting scenario is when
the SUSY breaking scale is larger than the compactification scale, but both are
small enough to be probed at the CERN LHC. Unification in two scales scenarios
is also investigated and found to give results within the LHC.Comment: 17 pages, 3 figures, some discussions added, few additional
references included. Version to appear in Phys. Rev.
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