86 research outputs found
Linearly-realised Worldsheet Supersymmetry in pp-wave Background
We study the linearly-realised worldsheet supersymmetries in the ``massive''
type II light-cone actions for pp-wave backgrounds. The pp-waves have have
16+N_sup Killing spinors, comprising 16 ``standard'' Killing spinors that occur
in any wave background, plus N_sup ``supernumerary'' Killing spinors (0\le
N_sup \le 16) that occur only for special backgrounds. We show that only the
supernumerary Killing spinors give rise to linearly-realised worldsheet
supersymmetries after light-cone gauge fixing, while the 16 standard Killing
spinors describe only non-linearly realised inhomogeneous symmetries. We also
study the type II actions in the physical gauge, and we show that although in
this case the actions are not free, there are now linearly-realised
supersymmetries coming both from the standard and the supernumerary Killing
spinors. In the physical gauge, there are no mass terms for any worldsheet
degrees of freedom, so the masses appearing in the light-cone gauge may be
viewed as gauge artefacts. We obtain type IIA and IIB supergravity solutions
describing solitonic strings in pp-wave backgrounds, and show how these are
related to the physical-gauge fundamental string actions. We study the
supersymmetries of these solutions, and find examples with various numbers of
Killing spinors, including total numbers that are odd.Comment: Latex, 35 page
A unique Z_4^R symmetry for the MSSM
We consider the possible anomaly free Abelian discrete symmetries of the MSSM
that forbid the mu-term at perturbative order. Allowing for anomaly
cancellation via the Green-Schwarz mechanism we identify discrete R-symmetries
as the only possibility and prove that there is a unique Z_4^R symmetry that
commutes with SO(10). We argue that non-perturbative effects will generate a
mu-term of electroweak order thus solving the mu-problem. The non-perturbative
effects break the Z_4^R symmetry leaving an exact Z_2 matter parity. As a
result dimension four baryon- and lepton-number violating operators are absent
while, at the non-perturbative level, dimension five baryon- and lepton-number
violating operators get induced but are highly suppressed so that the nucleon
decay rate is well within present bounds.Comment: 6 page
Toy model for a two-dimensional accretion disk dominated by Poynting flux
We discuss the effect of the Poynting flow on the magnetically dominated thin
accretion disk, which is simplified to a two-dimensional disk on the equatorial
plane. It is shown in the relativistic formulation that the Poynting flux by
the rotating magnetic field with Keplerian angular velocity can balance the
energy and angular momentum conservation of a steady accretion flow.Comment: 17 pages, no figure
Precise measurement of hadronic tau-decays with an eta meson
We have studied hadronic tau decay modes involving an eta meson using 490
fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy
e+e- collider. The following branching fractions have been measured: B(tau- ->
K- eta nu)=(1.58 +- 0.05 +- 0.09)x 10^{-4}, B(tau- -> K- pi0 eta nu)=(4.6 +-
1.1 +- 0.4)x 10^{-5}, B(tau- -> pi- pi0 eta nu)=(1.35 +- 0.03 +- 0.07)x
10^{-3}, B(tau- -> pi- KS eta nu)=(4.4 +- 0.7 +- 0.2)x 10^{-5}, and B(tau- ->
K^{*-} eta nu)=(1.34 +- 0.12 +- 0.09)x 10^{-4}. These results are substantially
more precise than previous measurements. The new measurements are compared with
theoretical calculations based on the CVC hypothesis or the chiral perturbation
theory. We also set upper limits on branching fractions for tau decays into K-
KS eta nu, pi- KS pi0 eta nu, K- eta eta nu, pi- eta eta nu and non-resonant K-
pi^0 eta nu final states.Comment: 24 pages, 7 figure
Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO
Gamma-ray bursts are believed to originate in core-collapse of massive stars.
This produces an active nucleus containing a rapidly rotating Kerr black hole
surrounded by a uniformly magnetized torus represented by two counter-oriented
current rings. We quantify black hole spin-interactions with the torus and
charged particles along open magnetic flux-tubes subtended by the event
horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of
frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with
GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii)
aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich
et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al.
2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating
LIGO/Virgo detectors enables searches for nearby events and their spectral
closure density 6e-9 around 250Hz in the stochastic background radiation in
gravitational waves. At current sensitivity, LIGO-Hanford may place an upper
bound around 150MSolar in GRB030329. Detection of Egw thus provides a method
for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49
Search for Resonant Decays at Belle
We report measurements and searches for resonant decays where is a
meson or
the X(3872) particle.Comment: accepted by Physics Letters
Search for B+ -> D*+ pi0 decay
We report on a search for the doubly Cabibbo suppressed decay B+ -> D*+ pi0,
based on a data sample of 657 million BBbar pairs collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider.
We find no significant signal and set an upper limit of Br(B+ -> D*+ pi0) < 3.6
x 10^-6 at the 90% confidence level. This limit can be used to constrain the
ratio between suppressed and favored B -> D* pi decay amplitudes, r < 0.051, at
the 90% confidence level.Comment: 5pages, 2figures, submitted to PRL (v1); PRL published version (v2:
minor corrections in the text
Search for B -> h(*) nu nubar Decays at Belle
We present a search for the rare decays B -> h(*) nu nubar, where h(*) stands
for a light meson. A data sample of 535 million BBbar pairs collected with the
Belle detector at the KEKB e+e- collider is used. Signal candidates are
required to have an accompanying B meson fully reconstructed in a hadronic mode
and signal-side particles consistent with a single h(*) meson. No significant
signal is observed and we set upper limits on the branching fractions at 90%
confidence level. The limits on B0 -> K*0 nu nubar and B+ -> K+ nu nubar decays
are more stringent than the previous constraints, while the first searches for
B0 -> K0 nu nubar, pi0 nu nubar, rho0 nu nubar, phi nu nubar and B+ -> K*+ nu
nubar, rho+ nu nubar are reported.Comment: 6 pages, 2 figures, submit to PR
Discrete R symmetries for the MSSM and its singlet extensions
We determine the anomaly free discrete R symmetries, consistent with the
MSSM, that commute with SU(5) and suppress the parameter and nucleon
decay. We show that the order M of such symmetries has to divide 24 and
identify 5 viable symmetries. The simplest possibility is a symmetry
which commutes with SO(10). We present a string-derived model with this
symmetry and the exact MSSM spectrum below the GUT scale; in this model
originates from the Lorentz symmetry of compactified dimensions. We extend the
discussion to include the singlet extensions of the MSSM and find and
are the only possible symmetries capable of solving the problem
in the NMSSM. We also show that a singlet extension of the MSSM based on a
symmetry can provide a simultaneous solution to the and strong
CP problem with the axion coupling in the favoured window.Comment: 44+1 pages, 2 figure
Search for Lepton Flavor Violating tau Decays into Three Leptons
We search for lepton-flavor-violating tau decays into three leptons (electron
or muon) using 535 fb-1 of data collected with the Belle detector at the KEKB
asymmetric-energy e+e- collider. No evidence for these decays is observed, and
we set 90% confidence level upper limits on the branching fractions of
(2.0-4.1)x10^-8. These results improve upon our previously published upper
limits by factors of 4.9 to 10.Comment: 11 pages, 4 figures, submitted to Phys. Lett.
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