41,947 research outputs found
Moduli Stabilization with the String Higgs Effect
We review the notion of the Higgs effect in the context of string theory. We
find that by including this effect in time dependent backgrounds, one is led to
a natural mechanism for stabilizing moduli at points of enhanced gauge
symmetry. We consider this mechanism for the case of the radion (size of the
extra dimensions) and find that as decompactification of the large spatial
dimensions takes place the radion will remain stabilized at the self dual
radius. We discuss how this mechanism can be incorporated into models of string
cosmology and brane inflation to resolve some outstanding problems. We also
address some issues regarding which string states should be included when
constructing low energy actions in string cosmology.Comment: 20 pages, references added, typos correcte
Geologic application of thermal-inertia mapping from satellite
The author has identified the following significant results. Two night-time thermal images of the Powder River Basin, Wyoming distinctly show a major thermal feature. This feature is substantially coincident with a drainage divide and the southward facing slope appears cooler, suggesting a lower thermal inertia. An initial examination of regional geologic maps provides no clear evidence to suggest what type of geologic feature or structure may be present, although it can be noted that its northeastern end passes directly through Lead, South Dakota where the Homestake Gold Mine is located
The Efficacy of Group Selection is Increased by Coexistence Dynamics within Groups
Selection on the level of loosely associated groups has been suggested as a route towards the evolution of cooperation between individuals and the subsequent formation of higher-level biological entities. Such group selection explanations remain problematic, however, due to the narrow range of parameters under which they can overturn within-group selection that favours selfish behaviour. In principle, individual selection could act on such parameters so as to strengthen the force of between-group selection and hence increase cooperation and individual fitness, as illustrated in our previous work. However, such a process cannot operate in parameter regions where group selection effects are totally absent, since there would be no selective gradient to follow. One key parameter, which when increased often rapidly causes group selection effects to tend to zero, is initial group size, for when groups are formed randomly then even moderately sized groups lack significant variance in their composition. However, the consequent restriction of any group selection effect to small sized groups is derived from models that assume selfish types will competitively exclude their more cooperative counterparts at within-group equilibrium. In such cases, diversity in the migrant pool can tend to zero and accordingly variance in group composition cannot be generated. In contrast, we show that if within-group dynamics lead to a stable coexistence of selfish and cooperative types, then the range of group sizes showing some effect of group selection is much larger
String Gas Cosmology
We present a critical review and summary of String Gas Cosmology. We include
a pedagogical derivation of the effective action starting from string theory,
emphasizing the necessary approximations that must be invoked. Working in the
effective theory, we demonstrate that at late-times it is not possible to
stabilize the extra dimensions by a gas of massive string winding modes. We
then consider additional string gases that contain so-called enhanced symmetry
states. These string gases are very heavy initially, but drive the moduli to
locations that minimize the energy and pressure of the gas. We consider both
classical and quantum gas dynamics, where in the former the validity of the
theory is questionable and some fine-tuning is required, but in the latter we
find a consistent and promising stabilization mechanism that is valid at
late-times. In addition, we find that string gases provide a framework to
explore dark matter, presenting alternatives to CDM as recently
considered by Gubser and Peebles. We also discuss quantum trapping with string
gases as a method for including dynamics on the string landscape.Comment: 55 pages, 1 figure, minor corrections, version to appear in Reviews
of Modern Physic
Dynamical decompactification from brane gases in eleven-dimensional supergravity
Brane gas cosmology provides a dynamical decompactification mechanism that
could account for the number of spacetime dimensions we observe today. In this
work we discuss this scenario taking into account the full bosonic sector of
eleven-dimensional supergravity. We find new cosmological solutions that can
dynamically explain the existence of three large spatial dimensions
characterised by an universal asymptotic scaling behaviour and a large number
of initially unwrapped dimensions. This type of solutions enlarge the possible
initial conditions of the Universe in the Hagedorn phase and consequently can
potentially increase the probability of dynamical decompactification from
anisotropically wrapped backgrounds.Comment: 8 figures, JHEP3 styl
Target space duality and moduli stabilization in String Gas Cosmology
Motivated by string gas cosmology, we investigate the stability of moduli
fields coming from compactifications of string gas on torus with background
flux. It was previously claimed that moduli are stabilized only at a single
fixed point in moduli space, a self-dual point of T-duality with vanishing
flux. Here, we show that there exist other stable fixed points on moduli space
with non-vanishing flux. We also discuss the more general target space
dualities associated with these fixed points.Comment: 12 pages, 1 figur
Geologic applications of thermal-inertia mapping from satellite
In the Powder River Basin, Wyo., narrow geologic units having thermal inertias which contrast with their surroundings can be discriminated in optimal images. A few subtle thermal inertia anomalies coincide with areas of helium leakage believed to be associated with deep oil and gas concentrations. The most important results involved delineation of tectonic framework elements some of which were not previously recognized. Thermal and thermal inertia images also permit mapping of geomorphic textural domains. A thermal lineament appears to reveal a basement discontinuity which involves the Homestake Mine in the Black Hill, a zone of Tertiary igneous activity and facies control in oil producing horizons. Applications of these data to the Cabeza Prieta, Ariz., area illustrate their potential for igneous rock type discrimination. Extension to Yellowstone National Park resulted in the detection of additional structural information but surface hydrothermal features could not be distinguished with any confidence. A thermal inertia mapping algorithm, a fast and accurate image registration technique, and an efficient topographic slope and elevation correction method were developed
Effective Field Theory Approach to String Gas Cosmology
We derive the 4D low energy effective field theory for a closed string gas on
a time dependent FRW background. We examine the solutions and find that
although the Brandenberger-Vafa mechanism at late times no longer leads to
radion stabilization, the radion rolls slowly enough that the scenario is still
of interest. In particular, we find a simple example of the string inspired
dark matter recently proposed by Gubser and Peebles.Comment: 19 pages, 2 figures, comments adde
Geologic application of thermal-inertia mapping from satellite
The author has identified the following significant results. Approximately 400 miles of low altitude scanner data of good quality was acquired over the Powder River Basin between 13-16 Oct. 1978. Radiometric and meteorological data from three ground stations were also acquired in support of low altitude U.S.G.S. overflights
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