709 research outputs found
Freund-Rubin Revisited
We utilise the duality between M theory and Type IIA string theory to show
the existence of Freund-Rubin compactifications of M theory on 7-manifolds with
singularities supporting chiral fermions. This leads to a concrete way to study
phenomenologically interesting quantum gravity vacua using a holographically
dual three dimensional field theory.Comment: reference adde
Rare Decay Modes of Quarter BPS Dyons
The degeneracy of quarter BPS dyons in N=4 supersymmetric string theories is
known to jump across walls of marginal stability on which a quarter BPS dyon
can decay into a pair of half BPS dyons. We show that as long as the electric
and magnetic charges of the original dyon are primitive elements of the charge
lattice, the subspaces of the moduli space on which a quarter BPS dyon becomes
marginally unstable against decay into a pair of quarter BPS dyons or a half
BPS dyon and a quarter BPS dyon are of codimension two or more. As a result any
pair of generic points in the moduli space can be connected by a path avoiding
these subspaces and there is no jump in the spectrum associated with these
subspaces.Comment: LaTeX file, 9 pages; v2: a minor logical error corrected with no
change in the result
Constructible motivic functions and motivic integration
We introduce a direct image formalism for constructible motivic functions.
One deduces a very general version of motivic integration for which a change of
variables theorem is proved. These constructions are generalized to the
relative framework, in which we develop a relative version of motivic
integration. These results have been announced in math.AG/0403349 and
math.AG/0403350.
Main results and statements unchanged. Many minor slips corrected and some
details added.Comment: Final versio
Two Centered Black Holes and N=4 Dyon Spectrum
The exact spectrum of dyons in a class of N=4 supersymmetric string theories
is known to change discontinuously across walls of marginal stability. We show
that the change in the degeneracy across the walls of marginal stability can be
accounted for precisely by the entropy of two centered small black holes which
disappear as we cross the walls of marginal stability.Comment: LaTeX file, 12 pages; v3: added footnote 2 regarding overall sign of
the index, expanded footnote 3, added reference
Integration over a space of non-parametrized arcs, and motivic analogues of the monodromy zeta function
Notions of integration of motivic type over the space of arcs factorized by the natural C*-action and over the space of nonparametrized arcs (branches) are developed. As an application, two motivic versions of the zeta function of the classical monodromy transformation of a germ of an analytic function on ℂd are given that correspond to these notions. Another key ingredient in the construction of these motivic versions of the zeta function is the use of the so-called power structure over the Grothendieck ring of varieties introduced by the authors
Signals of Inflation in a Friendly String Landscape
Following Freivogel {\it et al} we consider inflation in a predictive (or
`friendly') region of the landscape of string vacua, as modeled by
Arkani-Hamed, Dimopoulos and Kachru. In such a region the dimensionful
coefficients of super-renormalizable operators unprotected by symmetries, such
as the vacuum energy and scalar mass-squareds are freely scanned over, and the
objects of study are anthropically or `environmentally' conditioned probability
distributions for observables. In this context we study the statistical
predictions of (inverted) hybrid inflation models, where the properties of the
inflaton are probabilistically distributed. We derive the resulting
distributions of observables, including the deviation from flatness
, the spectral index of scalar cosmological perturbations
(and its scale dependence ), and the ratio of tensor to scalar
perturbations . The environmental bound on the curvature implies a solution
to the -problem of inflation with the predicted distribution of
indicating values close to current observations. We find a relatively low
probability () of `just-so' inflation with measurable deviations from
flatness. Intermediate scales of inflation are preferred in these models.Comment: 20 pages, 11 figure
Dirac Action on M5 and M2 Branes with Bulk Fluxes
We derive an explicit form of the quadratic in fermions Dirac action on the
M5 brane for an arbitrary on-shell background of 11D supergravity with
non-vanishing fluxes and in presence of a chiral 2-form on M5. This action may
be used to generalize the conditions for which the non-perturbative
superpotential can be generated in M/string theory. We also derive the Dirac
action with bulk fluxes on the M2 brane.Comment: 12 pages References adde
More Bubbling Solutions
In this note we construct families of asymptotically flat, smooth,
horizonless solutions with a large number of non-trivial two-cycles (bubbles)
of N=1 five-dimensional supergravity with an arbitrary number of vector
multiplets, which may or may not have the charges of a macroscopic black hole
and which contain the known bubbling solutions as a sub-family. We do this by
lifting various multi-center BPS states of type IIA compactified on Calabi-Yau
three-folds and taking the decompactification (M-theory) limit. We also analyse
various properties of these solutions, including the conserved charges, the
shape, especially the (absence of) throat and closed timelike curves, and
relate them to the various properties of the four-dimensional BPS states. We
finish by briefly commenting on their degeneracies and their possible relations
to the fuzzball proposal of Mathur et al.Comment: 36 pages, Latex; JHEP version, one appendix added, references adde
Cooper pairing near charged black holes
We show that a quartic contact interaction between charged fermions can lead
to Cooper pairing and a superconducting instability in the background of a
charged asymptotically Anti-de Sitter black hole. For a massless fermion we
obtain the zero mode analytically and compute the dependence of the critical
temperature T_c on the charge of the fermion. The instability we find occurs at
charges above a critical value, where the fermion dispersion relation near the
Fermi surface is linear. The critical temperature goes to zero as the marginal
Fermi liquid is approached, together with the density of states at the Fermi
surface. Besides the charge, the critical temperature is controlled by a four
point function of a fermionic operator in the dual strongly coupled field
theory.Comment: 1+33 pages, 4 figure
Best practice in police social media adaptation
Summary:
Best Practice in Police Social Media Adaptation.
This document describes best practice of European
police forces in adapting social media. The description
of these practices stems from a workshop series and
other events where police ICT experts met with academics
and industry experts; and from a study of the
Twitter usage of British police forces during the 2011
riots. Grouped in nine categories, we describe different
uses and implementation strategies of social media by
police forces. Based on these examples, we show that
there have been numerous ways in which police forces
benefitted from adopting social media, ranging from
improved information for investigations and an improved
relationship with the public to a more efficient
use of resources
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