5,577 research outputs found
An obstacle to populating the string theory landscape
We construct domain walls and instantons in a class of models with coupled
scalar fields, determining, in agreement with previous studies, that many such
solutions contain naked timelike singularities. Vacuum bubble solutions of this
type do not contain a region of true vacuum, obstructing the ability of eternal
inflation to populate other vacua. We determine a criterion that potentials
must satisfy to avoid the existence of such singularities, and show that many
domain wall solutions in Type IIB string theory are singular. This has profound
implications for applying the program of eternal inflation to making
predictions in the string theory landscape.Comment: 5 PRD style pages with 2 embedded figures. Replaced to match
published versio
Field dynamics and tunneling in a flux landscape
We investigate field dynamics and tunneling between metastable minima in a
landscape of Type IIB flux compactifications, utilizing monodromies of the
complex structure moduli space to continuously connect flux vacua. After
describing the generic features of a flux-induced potential for the complex
structure and Type IIB axio-dilaton, we specialize to the Mirror Quintic
Calabi--Yau to obtain an example landscape. Studying the cosmological dynamics
of the complex structure moduli, we find that the potential generically does
not support slow-roll inflation and that in general the landscape separates
neatly into basins of attraction of the various minima. We then discuss
tunneling, with the inclusion of gravitational effects, in many-dimensional
field spaces. A set of constraints on the form of the Euclidean paths through
field space are presented, and then applied to construct approximate instantons
mediating the transition between de Sitter vacua in the flux landscape. We find
that these instantons are generically thick-wall and that the tunneling rate is
suppressed in the large-volume limit. We also consider examples where
supersymmetry is not broken by fluxes, in which case near-BPS thin-wall bubbles
can be constructed. We calculate the bubble wall tension, finding that it
scales like a D- or NS-brane bubble, and comment on the implications of this
correspondence. Finally, we present a brief discussion of eternal inflation in
the flux-landscape.Comment: 23 PRD-style pages with 11 embedded figures. Added refs, corrected
typos, and clarified Sec. V. Replaced to match published versio
Runaway dilatonic domain walls
We explore the stability of domain wall and bubble solutions in theories with
compact extra dimensions. The energy density stored inside of the wall can
destabilize the volume modulus of a compactification, leading to solutions
containing either a timelike singularity or a region where space
decompactifies, depending on the metric ansatz. We determine the structure of
such solutions both analytically and using numerical simulations, and analyze
how they arise in compactifications of Einstein--Maxwell theory and Type IIB
string theory. The existence of instabilities has important implications for
the formation of networks of topological defects and the population of vacua
during eternal inflation.Comment: 29 pages with 19 figures. Replaced to match published versio
General relativistic effects in quantum interference of photons
Quantum mechanics and general relativity have been extensively and
independently confirmed in many experiments. However, the interplay of the two
theories has never been tested: all experiments that measured the influence of
gravity on quantum systems are consistent with non-relativistic, Newtonian
gravity. On the other hand, all tests of general relativity can be described
within the framework of classical physics. Here we discuss a quantum
interference experiment with single photons that can probe quantum mechanics in
curved space-time. We consider a single photon travelling in superposition
along two paths in an interferometer, with each arm experiencing a different
gravitational time dilation. If the difference in the time dilations is
comparable with the photon's coherence time, the visibility of the quantum
interference is predicted to drop, while for shorter time dilations the effect
of gravity will result only in a relative phase shift between the two arms. We
discuss what aspects of the interplay between quantum mechanics and general
relativity are probed in such experiments and analyze the experimental
feasibility.Comment: 16 pages, new appendix, published versio
Book review: will the Middle East implode? by Mohammed Ayoob
The Arab Spring has boosted both mainstream and radical Islamism, heightened the prospects of a third intifada, and exacerbated regional power rivalry in the Middle East. When adding these dynamics to the stalling Israel-Palestine conflict and ever-tense U.S.-Iran relations, the Middle East faces the prospect of a major implosion or a series of smaller, interconnected ones that could have implications for regional global security, argues Mohammed Ayoob. Magdalena C. Delgado finds this to be an accessible and analytically rich book suitable for general readers looking for an up to date account of the topic
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