9 research outputs found
Chiral Topologically Massive Gravity and Extremal B-F Scalars
At a critical ``chiral'' coupling, topologically massive gravity with a
negative cosmological constant exhibits several unusual features, including the
emergence of a new logarithmic branch of solutions and a linearization
instability for certain boundary conditions. I show that at this coupling, the
linearized theory may be parametrized by a free scalar field at the
Breitenlohner-Freedman bound, and use this description to investigate these
features.Comment: 16 pages; v2: added references, typos correcte
A Space-Time Orbifold: A Toy Model for a Cosmological Singularity
We explore bosonic strings and Type II superstrings in the simplest time
dependent backgrounds, namely orbifolds of Minkowski space by time reversal and
some spatial reflections. We show that there are no negative norm physical
excitations. However, the contributions of negative norm virtual states to
quantum loops do not cancel, showing that a ghost-free gauge cannot be chosen.
The spectrum includes a twisted sector, with strings confined to a ``conical''
singularity which is localized in time. Since these localized strings are not
visible to asymptotic observers, interesting issues arise regarding unitarity
of the S-matrix for scattering of propagating states. The partition function of
our model is modular invariant, and for the superstring, the zero momentum
dilaton tadpole vanishes. Many of the issues we study will be generic to
time-dependent cosmological backgrounds with singularities localized in time,
and we derive some general lessons about quantizing strings on such spaces.Comment: 21 pages, 2 figure
Quiver theories, soliton spectra and Picard-Lefschetz transformations
Quiver theories arising on D3-branes at orbifold and del Pezzo singularities
are studied using mirror symmetry. We show that the quivers for the orbifold
theories are given by the soliton spectrum of massive 2d N=2 theory with
weighted projective spaces as target. For the theories obtained from the del
Pezzo singularities we show that the geometry of the mirror manifold gives
quiver theories related to each other by Picard-Lefschetz transformations, a
subset of which are simple Seiberg duals. We also address how one indeed
derives Seiberg duality on the matter content from such geometrical transitions
and how one could go beyond and obtain certain ``fractional Seiberg duals.''
Moreover, from the mirror geometry for the del Pezzos arise certain Diophantine
equations which classify all quivers related by Picard-Lefschetz. Some of these
Diophantine equations can also be obtained from the classification results of
Cecotti-Vafa for the 2d N=2 theories.Comment: 34 pages, 11 figure
Spontaneous CP Violation in Non-Minimal Supersymmetric Models
We study the possibilities of spontaneous CP violation in the Next-to-Minimal
Supersymmetric Standard Model with an extra singlet tadpole term in the scalar
potential. We calculate the Higgs boson masses and couplings with radiative
corrections including dominant two loop terms. We show that it is possible to
satisfy the LEP constraints on the Higgs boson spectrum with non-trivial
spontaneous CP violating phases. We also show that these phases could account
for the observed value of epsilonK.Comment: 21 pages, 7 Figures in Encapsulated Postscrip
Higgs and neutrino sector, EDM and epsilon_K in a spontaneously CP and R-parity breaking supersymmetric model
We construct an extension of the supersymmetric standard model where both CP
symmetry and R-parity are spontaneously broken. We study the electroweak
symmetry breaking sector of the model and find minima consistent with the
experimental bounds on Higgs boson masses. Neutrino masses and mixing angles
are generated through both seesaw and bilinear R-parity violation. We show that
the hierarchical mass pattern is obtained, and mixings are consistent with
measured values. Due to the spontaneous CP and R-parity violation, the neutrino
sector is CP violating, and we calculate the corresponding phase. We further
restrict the parameter space to agree with the limits on the electric dipole
moment of the neutron. Finally, we study the CP violation parameter epsilon_K
in the kaon system and show that we obtain results consistent with the
experimental value.Comment: 13 pages, 7 figures, submitted to EPJ