2,518 research outputs found
Bubble Universe Dynamics After Free Passage
We consider bubble collisions in single scalar field theories with multiple
vacua. Recent work has argued that at sufficiently high impact velocities,
collisions between such bubble vacua are governed by 'free passage' dynamics in
which field interactions can be ignored during the collision, providing a
systematic process for populating local minima without quantum nucleation. We
focus on the time period that follows the bubble collision and provide evidence
that, for certain potentials, interactions can drive significant deviations
from the free-passage bubble profile, thwarting the production of bubbles with
different field values.Comment: 21pages, 8 figures, Revised version modified to include
Acknowledgements sectio
Dynamical Topology Change in M Theory
We study topology change in M theory compactifications on Calabi-Yau
three-folds in the presence of G flux (the four form field strength). In
particular, we discuss vacuum solutions in strongly coupled heterotic string
theory in which the topology change is inevitable within a single spacetime
background. For rather generic choices of initial conditions, the field
equations drive the Kahler moduli outside the classical moduli space of a
Calabi-Yau manifold. Consistency of the solution suggests that degenerate flop
curves - just as wrapped M theory fivebranes - carry magnetic charges under the
four form field strength.Comment: 21 pages, LaTeX, 2 figures (eps
D-Brane Topology Changing Transitions
We study D-branes on three-dimensional orbifold backgrounds that admit
topologically distinct resolutions differing by flop transitions. We show that
these distinct phases are part of the vacuum moduli space of the super
Yang-Mills gauge theory describing the D-brane dynamics. In this way we
establish that D-branes --- like fundamental strings --- allow for physically
smooth topology changing transitions.Comment: 16 pages, 3 figures, Harvma
Summary Report for National Aeronautics Space Administration (NASA) and Centro Para Prevencao da Poluicao (C3P) 2011 International Workshop on Environment and Alternative Energy
The C3P &. NASA International Workshop on Environment and Alternative Energy was held on November 15-18, 2011 at the European Space Agency (ESA)'s Research and Technology Centre (ESTEC) in Noordwijk, The Netherlands. The theme of the workshop was "Global Collaboration in Environmental and Alternative Energy Strategies". The workshop was held at ESTEC's conference center. More than 110 individuals from eleven countries attended the workshop. For the first time since the inception of NASA-C3P workshops, a full day was dedicated to a student session. Fifteen students from around the globe gave oral presentations along with poster displays relating to the latest technologies in environmental and alternative energy strategies. Judges from NASA, C3P and ESA awarded plaques to the top three students. In addition to the students, thirty eight U.S. and international subject matter experts presented on the following general environmental-related topics: (1) Hazardous materials management and substitution in support of space operations (2) Emerging renewable and alternative energy technologies (3) Sustainable development and redevelopment (4) Remediation technologies and strategies The workshop also included a panel discussion on the topic of the challenges of operating installations across borders. Throughout the workshop, attendees heard about the scope of environmental and energy challenges that industry and governments face. They heard about technologies for increasing energy efficiency and increasing use of renewable energy. They learned about ways companies and government agencies are using materials, processes, goods and services in a manner more respectful with the environment and in compliance with health and safety rules. The concept of partnerships and their inherent benefits was evidenced throughout the workshop. Partnering is a key aspect of sustainability because sustainable development is complicated. Through formal presentations and side discussions, attendees commented on the need for continued exploration of joint projects of mutual interest
Bouncing and cyclic string gas cosmologies
We show that, in the presence of a string gas, simple higher-derivative
modifications to the effective action for gravity can lead to bouncing and
cyclic cosmological models. The modifications bound the expansion rate and
avoid singularities at finite times. In these models the scale factors can have
long loitering phases that solve the horizon problem. Adding a potential for
the dilaton gives a simple realization of the pre-big bang scenario. Entropy
production in the cyclic phase drives an eventual transition to a
radiation-dominated universe. As a test of the Brandenberger-Vafa scenario, we
comment on the probability of decompactifying three spatial dimensions in this
class of models.Comment: 35 pages, LaTeX, 9 figures. v2: additional references. v3: comments
on Einstein frame, version to appear in PR
A bulk inflaton from large volume extra dimensions
The universe may have extra spatial dimensions with large volume that we
cannot perceive because the energy required to excite modes in the extra
directions is too high. Many examples are known of such manifolds with a large
volume and a large mass gap. These compactifications can help explain the
weakness of four-dimensional gravity and, as we show here, they also have the
capacity to produce reasonable potentials for an inflaton field. Modeling the
inflaton as a bulk scalar field, it becomes very weakly coupled in four
dimensions, and this enables us to build phenomenologically acceptable
inflationary models with tunings at the few per mil level. We speculate on dark
matter candidates and the possibility of braneless models in this setting.Comment: 21 pages, LaTeX, 2 pdf figures. v2: additional references. v3: added
comments on moduli stabilizatio
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