71 research outputs found
Decay of flux vacua to nothing
We construct instanton solutions describing the decay of flux
compactifications of a gauge theory by generalizing the Kaluza-Klein
bubble of nothing. The surface of the bubble is described by a smooth
magnetically charged solitonic brane whose asymptotic flux is precisely that
responsible for stabilizing the 4d compactification. We describe several
instances of bubble geometries for the various vacua occurring in a
Einstein-Maxwell theory namely, AdS_4 x S^2, R^{1,3} x S^2, and dS_4 x S^2.
Unlike conventional solutions, the bubbles of nothing introduced here occur
where a {\em two}-sphere compactification manifold homogeneously degenerates.Comment: 31 pages, 15 figure
An Exercise in Reverse Engineering for Safety-Critical Systems: An Experience for the Classroom
Since the Y2K crisis, reverse engineering has become a major area of work in industrial software application development, but lacks emphasis in US academia. This issue is exemplified by the high demand for software systems in new and expanding software application areas, which has resulted in systems being implemented before the requirements and design phases have been completed. Towards the maintenance of such systems, it is necessary to conducted reverse engineering for the derivation of software documentation for requirements and high-level and low-level design. When this scenario exists in the domain of safety-critical system, particularly in the aviation industry, reverse engineering takes on greater value because such software systems have to undergo development regulations and certification restrictions. This work reports on the pedagogical revelations gained from conducting reverse engineering on a software system that was developed and deployed for use in managing the assignment of commercial aircrafts to airport terminal gates. The software system incorporated genetic algorithms solutions and was implemented on a high-speed multi-processor system. The reverse engineering methodology applied was based on the RTCA DO-178C Software Considerations in Airborne Systems and Equipment Certification specification for onboard avionic software systems
Bubbles from Nothing
Within the framework of flux compactifications, we construct an instanton
describing the quantum creation of an open universe from nothing. The solution
has many features in common with the smooth 6d bubble of nothing solutions
discussed recently, where the spacetime is described by a 4d compactification
of a 6d Einstein-Maxwell theory on S^2 stabilized by flux. The four-dimensional
description of this instanton reduces to that of Hawking and Turok. The choice
of parameters uniquely determines all future evolution, which we additionally
find to be stable against bubble of nothing instabilities.Comment: 19 pages, 6 figure
Stochastic Inflation Revisited: Non-Slow Roll Statistics and DBI Inflation
Stochastic inflation describes the global structure of the inflationary
universe by modeling the super-Hubble dynamics as a system of matter fields
coupled to gravity where the sub-Hubble field fluctuations induce a stochastic
force into the equations of motion. The super-Hubble dynamics are ultralocal,
allowing us to neglect spatial derivatives and treat each Hubble patch as a
separate universe. This provides a natural framework in which to discuss
probabilities on the space of solutions and initial conditions. In this article
we derive an evolution equation for this probability for an arbitrary class of
matter systems, including DBI and k-inflationary models, and discover
equilibrium solutions that satisfy detailed balance. Our results are more
general than those derived assuming slow roll or a quasi-de Sitter geometry,
and so are directly applicable to models that do not satisfy the usual slow
roll conditions. We discuss in general terms the conditions for eternal
inflation to set in, and we give explicit numerical solutions of highly
stochastic, quasi-stationary trajectories in the relativistic DBI regime.
Finally, we show that the probability for stochastic/thermal tunneling can be
significantly enhanced relative to the Hawking-Moss instanton result due to
relativistic DBI effects.Comment: 38 pages, 2 figures. v3: minor revisions; version accepted into JCA
Reconnection of Non-Abelian Cosmic Strings
Cosmic strings in non-abelian gauge theories naturally gain a spectrum of
massless, or light, excitations arising from their embedding in color and
flavor space. This opens up the possibility that colliding strings miss each
other in the internal space, reducing the probability of reconnection. We study
the topology of the non-abelian vortex moduli space to determine the outcome of
string collision. Surprisingly we find that the probability of classical
reconnection in this system remains unity, with strings passing through each
other only for finely tuned initial conditions. We proceed to show how this
conclusion can be changed by symmetry breaking effects, or by quantum effects
associated to fermionic zero modes, and present examples where the probability
of reconnection in a U(N) gauge theory ranges from 1/N for low-energy
collisions to one at higher energies.Comment: 25 Pages, 3 Figures. v2: comment added, reference adde
Duality Cascade in Brane Inflation
We show that brane inflation is very sensitive to tiny sharp features in
extra dimensions, including those in the potential and in the warp factor. This
can show up as observational signatures in the power spectrum and/or
non-Gaussianities of the cosmic microwave background radiation (CMBR). One
general example of such sharp features is a succession of small steps in a
warped throat, caused by Seiberg duality cascade using gauge/gravity duality.
We study the cosmological observational consequences of these steps in brane
inflation. Since the steps come in a series, the prediction of other steps and
their properties can be tested by future data and analysis. It is also possible
that the steps are too close to be resolved in the power spectrum, in which
case they may show up only in the non-Gaussianity of the CMB temperature
fluctuations and/or EE polarization. We study two cases. In the slow-roll
scenario where steps appear in the inflaton potential, the sensitivity of brane
inflation to the height and width of the steps is increased by several orders
of magnitude comparing to that in previously studied large field models. In the
IR DBI scenario where steps appear in the warp factor, we find that the
glitches in the power spectrum caused by these sharp features are generally
small or even unobservable, but associated distinctive non-Gaussianity can be
large. Together with its large negative running of the power spectrum index,
this scenario clearly illustrates how rich and different a brane inflationary
scenario can be when compared to generic slow-roll inflation. Such distinctive
stringy features may provide a powerful probe of superstring theory.Comment: Corrections in Eq.(5.47), Eq (5.48), Eq(5.49) and Fig
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