9,583 research outputs found
The Manifestly Sl(2;Z)-covariant Superstring
We present a manifestly Sl(2;Z)-covariant action for the type IIB
superstring, and prove kappa-symmetry for on-shell IIB supergravity
backgrounds.Comment: 13 pages, plain tex. Two minor corrections. Reference adde
Accelerating Cosmologies from S-Branes
We point out that the recently proposed model of a flat 4-dimensional
universe with accelerated expansion in string/M-theory is a special case of
time-dependent solutions that the author found under the name of ``S-branes.''
We also show that similar accelerating models can be obtained from S-branes if
the internal space is chosen to be hyperbolic or flat spaces.Comment: 8 pages, 4 figures, comments added, a typo corrected, final version
to appear in Phys. Rev. Let
Axion-Dilaton Domain Walls and Fake Supergravity
Dynamical systems methods are used to investigate domain-wall solutions of a
two-parameter family of models in which gravity is coupled to an axion, and to
a dilaton with an exponential potential of either sign. A complete global
analysis is presented for (i) constant axion and (ii) flat walls, including a
study of bifurcations and a new exact domain-wall solution with non-constant
axion. We reconsider `fake supergravity' issues in light of these results. We
show, by example, how domain walls determine multi-valued superpotentials that
branch at stationary points that are not stationary points of the potential,
and we apply this result to potentials with anti-de Sitter vacua. We also show
by example that `adapted' truncation to a single-scalar model is sometimes
inconsistent, and we propose a `generalized' fake supergravity formalism that
applies in some such cases.Comment: 43pp, 19 figures; minor corrections and extensions; one additional
figur
The Heterotic Dyonic Instanton
The static Yang-Mills-Higgs dyonic instanton is shown to have a
non-vanishing, but anti-self-dual, angular momentum 2-form with skew
eigenvalues equal to the electric charge; for large charge the angular momentum
causes the instanton to expand into a hyper-spherical shell. A class of exact
multi dyonic instantons is then found and then generalized to a new class of
1/4 supersymmetric, non-singular, stationary, exact solutions of the
ten-dimensional supergravity/Yang-Mills theory. These self-gravitating dyonic
instantons yield new heterotic string solitons, to leading order in the inverse
string tension.Comment: 18 pages, LaTeX, no figures. Previous revision was to include exact
multi-solitons. Third version corrects typos and ADM energy formul
Supersymmetric Electrovacs In Gauged Supergravities
We show that the D=6 SU(2) gauged supergravity of van Nieuwenhuizen et al,
obtained by dimensional reduction of the D=7 topologically massive gauged
supergravity and previously thought not to be dimensionally reducible, can be
further reduced to five and four dimensions. On reduction to D=4 one recovers
the special case of the SU(2)XSU(2) gauged supergravity of Freedman and Schwarz
for which one of the SU(2) coupling constants vanishes. Previously known
supersymmetric electrovacs of this model then imply new ground states in 7-D.
We construct a supersymmetric electrovac solution of N=2 SU(2) gauged
supergravity in 7-D. We also investigate the domain wall solutions of these
theories and show they preserve a half of the supersymmetry.Comment: 29 pages, TeX, no figures. Introduction and conclusion rewritten. New
references added. Minor changes to all section
Vibration signature analysis of multistage gear transmission
An analysis is presented for multistage multimesh gear transmission systems. The analysis predicts the overall system dynamics and the transmissibility to the gear box or the enclosed structure. The modal synthesis approach of the analysis treats the uncoupled lateral/torsional model characteristics of each stage or component independently. The vibration signature analysis evaluates the global dynamics coupling in the system. The method synthesizes the interaction of each modal component or stage with the nonlinear gear mesh dynamics and the modal support geometry characteristics. The analysis simulates transient and steady state vibration events to determine the resulting torque variations, speeds, changes, rotor imbalances, and support gear box motion excitations. A vibration signature analysis examines the overall dynamic characteristics of the system, and the individual model component responses. The gear box vibration analysis also examines the spectral characteristics of the support system
Multiple M-wave interaction with fluxes
We present the equations of motion for multiple M0-brane (multiple M-wave or
mM0) system in general eleven dimensional supergravity background. These are
obtained in the frame of superembedding approach, but have a rigid structure:
they can be restored from SO(1,1) x SO(9) symmetry characteristic for M0. BPS
conditions for the 1/2 supersymmetric solution of these equations have the
fuzzy 2-sphere solution describing M2-brane.Comment: 4 pages, no figures, RevTeX4. V2. The discussion on BPS conditions
and some supersymmetric solutions is added. The explicit values of the
coefficients for the interacting terms are presented. Also a couple of minor
changes. V3: a small misrint corrected. Published: Phys.Rev.Lett.105 (2010)
07160
Diagnostics Of Disks Around Hot Stars
We discuss three different observational diagnostics related to disks around hot stars: absorption line determinations of rotational velocities of Be stars; polarization diagnostics of circumstellar disks; and X-ray line diagnostics of one specific magnetized hot star, theta(1) Ori C. Some common themes that emerge from these studies include (a) the benefits of having a specific physical model as a framework for interpreting diagnostic data; (b) the importance of combining several different types of observational diagnostics of the same objects; and (c) that while there is often the need to reinterpret traditional diagnostics in light of new theoretical advances, there are many new and powerful diagnostics that are, or will soon be, available for the study of disks around hot stars
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