28,993 research outputs found
Observing The Hidden Sector
We study the effects of renormalization due to hidden-sector dynamics on
observable soft supersymmetry-breaking parameters in the minimal supersymmetric
extension of the Standard Model (MSSM), under various hypotheses about their
universality at a high input scale. We show that hidden-sector renormalization
effects may induce the spurious appearance of unification of the scalar masses
at some lower scale, as in mirage unification scenarios. We demonstrate in
simple two-parameter models of the hidden-sector dynamics that the parameters
may in principle be extracted from experimental measurements, rendering the
hidden sector observable. We also discuss the ingredients that would be
necessary to carry this programme out in practice.Comment: 38 pages, 13 figures, uses UApreprint.cls and subfigure.sty
(included
Jet Investigations Using the Radial Moment
We define the radial moment, , for jets produced in hadron-hadron
collisions. It can be used as a tool for studying, as a function of the jet
transverse energy and pseudorapidity, radiation within the jet and the quality
of a perturbative description of the jet shape. We also discuss how
non-perturbative corrections to the jet transverse energy affect .Comment: 14 pages, LaTeX, 6 figure
A Note on Infinities in Eternal Inflation
In some well-known scenarios of open-universe eternal inflation, developed by
Vilenkin and co-workers, a large number of universes nucleate and thermalize
within the eternally inflating mega-universe. According to the proposal, each
universe nucleates at a point, and therefore the boundary of the nucleated
universe is a space-like surface nearly coincident with the future light cone
emanating from the point of nucleation, all points of which have the same
proper-time. This leads the authors to conclude that at the proper-time t =
t_{nuc} at which any such nucleation occurs, an infinite open universe comes
into existence. We point out that this is due entirely to the supposition of
the nucleation occurring at a single point, which in light of quantum cosmology
seems difficult to support. Even an infinitesimal space-like length at the
moment of nucleation gives a rather different result -- the boundary of the
nucleating universe evolves in proper-time and becomes infinite only in an
infinite time. The alleged infinity is never attained at any finite time.Comment: 13 pages and 6 figure
Numerical evaluation of one-loop QCD amplitudes
We present the publicly available program NGluon allowing the numerical
evaluation of primitive amplitudes at one-loop order in massless QCD. The
program allows the computation of one-loop amplitudes for an arbitrary number
of gluons. The focus of the present article is the extension to one-loop
amplitudes including an arbitrary number of massless quark pairs. We discuss in
detail the algorithmic differences to the pure gluonic case and present cross
checks to validate our implementation. The numerical accuracy is investigated
in detail.Comment: Talk given at ACAT 2011 conference in London, 5-9 Septembe
Dynamics of Inflationary Universes with Positive Spatial Curvature
If the spatial curvature of the universe is positive, then the curvature term
will always dominate at early enough times in a slow-rolling inflationary
epoch. This enhances inflationary effects and hence puts limits on the possible
number of e-foldings that can have occurred, independently of what happened
before inflation began and in particular without regard for what may have
happened in the Planck era. We use a simple multi-stage model to examine this
limit as a function of the present density parameter and the epoch
when inflation ends.Comment: 9 Pages RevTex4. Revised and update
Eddy current damper
A high torque capacity eddy current damper used as a rate limiting device for a large solar array deployment mechanism is discussed. The eddy current damper eliminates the problems associated with the outgassing or leaking of damping fluids. It also provides performance advantages such as damping torque rates, which are truly linear with respect to input speed, continuous 360 degree operation in both directions of rotation, wide operating temperature range, and the capability of convenient adjustment of damping rates by the user without disassembly or special tools
Preliminary study of creep thresholds and thermomechanical response in Haynes 188 at temperatures in the range 649 to 871 C
The following conclusions were drawn from this study of creep thresholds and thermomechanical response: (1) creep threshold can be determined using the latest electrohydraulic test equipment, providing that test durations are short and relatively large accumulations of creep strain are used in defining the threshold; (2) significant creep strains were measured under monotonic loading as stress levels as low as 4 ksi at temperatures predicted for solar receiver service; and (3) the material exhibited creep ratchetting during simulated service cycles, a result not predicted by analysis using current constitutive models for Haynes 188
Closed Trapped Surfaces in Cosmology
The existence of closed trapped surfaces need not imply a cosmological
singularity when the spatial hypersurfaces are compact. This is illustrated by
a variety of examples, in particular de Sitter spacetime admits many closed
trapped surfaces and obeys the null convergence condition but is non-singular
in the k=+1 frame.Comment: 11 pages. To appear in GRG, Vol 35 (August issue
Consistency of dust solutions with div H=0
One of the necessary covariant conditions for gravitational radiation is the
vanishing of the divergence of the magnetic Weyl tensor H_{ab}, while H_{ab}
itself is nonzero. We complete a recent analysis by showing that in
irrotational dust spacetimes, the condition div H=0 evolves consistently in the
exact nonlinear theory.Comment: 3 pages Revte
Dynamical Formation of Horizons in Recoiling D Branes
A toy calculation of string/D-particle interactions within a world-sheet
approach indicates that quantum recoil effects - reflecting the gravitational
back-reaction on space-time foam due to the propagation of energetic particles
- induces the appearance of a microscopic event horizon, or `bubble', inside
which stable matter can exist. The scattering event causes this horizon to
expand, but we expect quantum effects to cause it to contract again, in a
`bounce' solution. Within such `bubbles', massless matter propagates with an
effective velocity that is less than the velocity of light in vacuo, which may
lead to observable violations of Lorentz symmetry that may be tested
experimentally. The conformal invariance conditions in the interior geometry of
the bubbles select preferentially three for the number of the spatial
dimensions, corresponding to a consistent formulation of the interaction of D3
branes with recoiling D particles, which are allowed to fluctuate independently
only on the D3-brane hypersurface.Comment: 25 pages LaTeX, 4 eps figures include
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