Jason Kumar

Dark-Matter Particles without Weak-Scale Masses or Weak Interactions

We propose that dark matter is composed of particles that naturally have the correct thermal relic density, but have neither weak-scale masses nor weak interactions. These models emerge naturally from gauge-mediated supersymmetry breaking, where they elegantly solve the dark-matter problem. The framework accommodates single or multiple component dark matter, dark-matter masses from 10 MeV to 10 TeV, and interaction strengths from gravitational to strong. These candidates enhance many direct and indirect signals relative to weakly interacting massive particles and have qualitatively new implications for dark-matter searches and cosmological implications for colliders.

Isospin-Violating Dark Matter

Abstract Searches for dark matter scattering off nuclei are typically compared assuming that the dark matterʼs spin-independent couplings are identical for protons and neutrons. This assumption is neither innocuous nor well motivated. We consider isospin-violating dark matter (IVDM) with one extra parameter, the ratio of neutron to proton couplings, and include the isotope distribution for each detector. For a single choice of the coupling ratio, the DAMA and CoGeNT signals are consistent with each other and with current XENON constraints, and they unambiguously predict near future signals at XENON and CRESST. We provide a quark-level realization of IVDM as WIMPless dark matter that is consistent with all collider and low-energy bounds.

Vacuum Energy Cancellation in a Non-supersymmetric String

The authors present a nonsupersymmetric orbifold of type 2 string theory and show that it has vanishing cosmological constant at the one and two loop level. They argue heuristically that the cancellation persists at higher loops.

Conformal theory of M2, D3, M5 and `D1+D5' branes

The bosonic actions for M2, D3 and M5 branes in their own d-dimensional near-horizon background are given in a manifestly SO(p+1,2) ? SO(d?p?1) invariant form (p = 2,3,5). These symmetries result from a breakdown of ISO(d,2) (with d = 10 for D3 and d = 11 for M2 and M5) symmetry by the Wess-Zumino term and constraints. The new brane actions, reduce after gauge-fixing and solving constraints to (p+1) dimensional interacting field theories with a non-linearly realized SO(p+1,2) conformal invariance. We also present an interacting two-dimensional conformal field theory on a D-string in the near-horizon geometry of a D1+D5 configuration.

Explaining the DAMA signal with WIMPless dark matter

Abstract WIMPless dark matter provides a framework in which dark matter particles with a wide range of masses naturally have the correct thermal relic density. We show that WIMPless dark matter with mass around 2–10 GeV can explain the annual modulation observed by the DAMA experiment without violating the constraints of other dark matter searches. This explanation implies distinctive and promising signals for other direct detection experiments, GLAST, and the LHC.

Scale dependent local non-gaussianity from loops

We analyze multi-field inflationary systems which yield strongly scale dependent non-Gaussianity with a shape that is very close to the local shape. As in usual multi-field models, the non-Gaussianity arises from the non-linear transfer of scalar field fluctuations to curvature perturbations. Here we consider models in which higher order terms (loops) dominate over the lowest order source of non-linearity. The magnitude of non-Gaussianity depends on an infrared cutoff which is determined by our observational probes measuring non-Gaussianity. In our models, the running is positive and large (nNG ~ 0.2) on CMB scales. The magnitude of the bispectrum is maximally of order (100), and grows on small scales. This can lead to interesting signals for large scale structure.

Matrix element analyses of dark matter scattering and annihilation

We provide a compendium of results at the level of matrix elements for a systematic study of dark matter scattering and annihilation. We identify interactions that yield spin-dependent and spin-independent scattering and specify whether the interactions are velocity- and/or momentum-suppressed. We identify the interactions that lead to s-wave or p-wave annihilation, and those that are chirality-suppressed. We also list the interaction structures that can interfere in scattering and annihilation processes. Using these results, we point out situations in which deviations from the standard lore are obtained.

Asymmetric Dark Matter from Hidden Sector Baryogenesis

Abstract We consider the production of asymmetric dark matter during hidden sector baryogenesis. We consider a particular supersymmetric model where the dark matter candidate has a number density approximately equal to the baryon number density, with a mass of the same scale as the b , c and τ . Both baryon asymmetry and dark matter are created at the same time in this model. We describe collider and direct detection signatures of this model.

Hadron and linear collider probes of hidden-sector gauge bosons

Intersecting D-brane theories motivate the existence of exotic U(1) gauge bosons that only interact with the Standard Model through kinetic mixing with hypercharge. We analyze an effective field theory description of this effect and describe the implications of these exotic gauge bosons on precision electroweak, LHC and ILC observables.

Special conformal symmetry of worldvolume actions

Kappa-symmetric worldvolume actions of the D3-, M5-, and M2-branes can be coupled consistently to their near horizon bosonic geometry background. We study the gauge-fixed action in the approximation in which only the transverse radial direction of the brane is allowed to fluctuate. The generalized special conformal symmetry of these self-interacting actions is established. This opens up the possibility to find out if the full superconformal symmetry of the free actions of these branes survives in the presence of coupling defined by the size of the anti{endash}de Sitter throat. {copyright} {ital 1998} {ital The American Physical Society}