6,427 research outputs found
Attractor Explosions and Catalyzed Vacuum Decay
We present a mechanism for catalyzed vacuum bubble production obtained by
combining moduli stabilization with a generalized attractor phenomenon in which
moduli are sourced by compact objects. This leads straightforwardly to a class
of examples in which the Hawking decay process for black holes unveils a bubble
of a different vacuum from the ambient one, generalizing the new endpoint for
Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble
production can occur for both charged and uncharged bodies, including
Schwarzschild black holes for which massive particles produced in the Hawking
process can trigger vacuum decay. We briefly discuss applications of this
process to the population and stability of metastable vacua.Comment: 26 pages harvmac big; 2 figure
Tension is Dimension
We propose a simple universal formula for the tension of a D-brane in terms
of a regularized dimension of the associated conformal field theory statespace.Comment: 18 pages, harvmac (b), one ref added, one typo fixe
Inelastic electron relaxation rates caused by Spin M/2 Kondo Impurities
We study a spin S=M/2--Kondo system coupled to electrons in an arbitrary
nonequilibrium situation above Kondo temperature. Coupling to hot electrons
leads to an increased inverse lifetime of pseudo particles, related to the
Korringa width. This in turn is responsible for the increased inelastic
relaxation rates of the electronic system. The rates are related to spin--spin
correlation functions which are determined using a projection operator
formalism. The results generalize recent findings for S=1/2--Kondo impurities
which have been used to describe energy relaxation experiments in disordered
mesoscopic wires.Comment: Brief Report, 4 page
Unitarity bounds and RG flows in time dependent quantum field theory
We generalize unitarity bounds on operator dimensions in conformal field
theory to field theories with spacetime dependent couplings. Below the energy
scale of spacetime variation of the couplings, their evolution can strongly
affect the physics, effectively shifting the infrared operator scaling and
unitarity bounds determined from correlation functions in the theory. We
analyze this explicitly for large- double-trace flows, and connect these to
UV complete field theories. One motivating class of examples comes from our
previous work on FRW holography, where this effect explains the range of
flavors allowed in the dual, time dependent, field theory.Comment: 38 page
Ground-Handling Forces on a 1/40-scale Model of the U. S. Airship "Akron."
This report presents the results of full-scale wind tunnel tests conducted to determine the ground-handling forces on a 1/40-scale model of the U. S. Airship "Akron." Ground-handling conditions were simulated by establishing a velocity gradient above a special ground board in the tunnel comparable with that encountered over a landing field. The tests were conducted at Reynolds numbers ranging from 5,000,000 to 19,000,000 at each of six angles of yaw between 0 degree and 180 degrees and at four heights of the model above the ground board. The ground-handling forces vary greatly with the angle of yaw and reach large values at appreciable angles of yaw. Small changes in height, pitch, or roll did not critically affect the forces on the model. In the range of Reynolds numbers tested, no significant variation of the forces with the scale was disclosed
A New Handle on de Sitter Compactifications
We construct a large new class of de Sitter (and anti de Sitter) vacua of
critical string theory from flux compactifications on products of Riemann
surfaces. In the construction, the leading effects stabilizing the moduli are
perturbative. We show that these effects self-consistently dominate over
standard estimates for further and quantum corrections, via
tuning available from large flux and brane quantum numbers.Comment: 26 pages, harvmac big. v2: Correction generalizing specific
ingredients required for tunable negative term; conclusions and structure of
potential unchange
On the Heterotic World-sheet Instanton Superpotential and its individual Contributions
For supersymmetric heterotic string compactifications on a Calabi-Yau
threefold endowed with a vector bundle the world-sheet superpotential
is a sum of contributions from isolated rational curves \C in ; the
individual contribution is given by an exponential in the K\"ahler class of the
curve times a prefactor given essentially by the Pfaffian which depends on the
moduli of and the complex structure moduli of . Solutions of (or
even of ) can arise either by nontrivial cancellations between the
individual terms in the summation over all contributing curves or because each
of these terms is zero already individually. Concerning the latter case
conditions on the moduli making a single Pfaffian vanish (for special moduli
values) have been investigated. However, even if corresponding moduli -
fulfilling these constraints - for the individual contribution of one curve are
known it is not at all clear whether {\em one} choice of moduli exists which
fulfills the corresponding constraints {\em for all contributing curves
simultaneously}. Clearly this will in general happen only if the conditions on
the 'individual zeroes' had already a conceptual origin which allows them to
fit together consistently. We show that this happens for a class of cases. In
the special case of spectral cover bundles we show that a relevant solution set
has an interesting location in moduli space and is related to transitions which
change the generation number.Comment: 47 page
Fine tuning and the ratio of tensor to scalar density fluctuations from cosmological inflation
The form of the inflationary potential is severely restricted if one requires
that it be natural in the technical sense, i.e. terms of unrelated origin are
not required to be correlated. We determine the constraints on observables that
are implied in such natural inflationary models, in particular on , the
ratio of tensor to scalar perturbations. We find that the naturalness
constraint does not require to be lare enough to be detectable by the
forthcoming searches for B-mode polarisation in CMB maps. We show also that the
value of is a sensitive discriminator between inflationary models.Comment: 8 pages LaTeX; clarifications and a reference added; to appear in
JCA
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