Search NASA⌕ Search

Engineering topics

Behbahani, Siavosh R.

Publications and source records attributed to Behbahani, Siavosh R..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

New natural shapes of non-Gaussianity from high-derivative interactions and their optimal limits from WMAP 9-year data

Given the fantastic experimental effort, it is important to thoroughly explore the signature space of inflationary models. The fact that higher derivative operators do not renormalize lower derivative ones allows us to find a large class of technically natural single-clock inflationary models where, in the context of the Effective Field Theory of Inflation, the leading interactions have many derivatives. We systematically explore the 3-point function induced by these models and their overlap with the standard equilateral and orthogonal templates. We find that in order to satisfactorily cover the signature space of these models, two new additional templates need to be included. We then perform the optimal analysis of the WMAP 9-year data for the resulting four templates, finding that the overall significance of a non-zero signal is between 2–2.5σ, depending on the choice of parameter space, partially driven by the preference for nonzero f{sub NL}{sup orth} in WMAP9.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

(Small) resonant non-gaussianities: signatures of a discrete shift symmetry in the effective field theory of inflation

We apply the Effective Field Theory of Inflation to study the case where the continuous shift symmetry of the Goldstone boson π is softly broken to a discrete subgroup. This case includes and generalizes recently proposed String Theory inspired models of Inflation based on Axion Monodromy. The models we study have the property that the 2-point function oscillates as a function of the wavenumber, leading to oscillations in the CMB power spectrum. The non-linear realization of time diffeomorphisms induces some self-interactions for the Goldstone boson that lead to a peculiar non-Gaussianity whose shape oscillates as a function of the wavenumber. We find that in the regime of validity of the effective theory, the oscillatory signal contained in the n−point correlation functions, with n > 2, is smaller than the one contained in the 2-point function, implying that the signature of oscillations, if ever detected, will be easier to find first in the 2-point function, and only then in the higher order correlation functions. Still the signal contained in higher-order correlation functions, that we study here in generality, could be detected at a subleading level, providing a very compelling consistency check for an approximate discrete shift symmetry being realized during inflation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Collective symmetry breaking and resonant non-gaussianity

We study inflationary models that produce a nearly scale-invariant power spectrum while breaking scale invariance significantly in the bispectrum. Under most circumstances, such models are finely-tuned, as radiative corrections generically induce a larger signal in the power spectrum. However, when scale invariance is broken collectively (i.e., it requires more than one coupling to break the symmetry), these radiative corrections may be suppressed. We illustrate the features and limitations of collective symmetry breaking in the context of resonant non-gaussianity. We discuss two examples where oscillatory features can arise predominantly in the bispectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Single-sector supersymmetry breaking, chirality, and unification

Calculable single-sector models provide an elegant framework for generating the flavor textures via compositeness, breaking supersymmetry, and explaining the electroweak scale. Such models may be realized naturally in supersymmetric QCD with additional gauge singlets, though it remains challenging to construct models without a surfeit of light exotic states where the standard model index emerges naturally. We classify possible single-sector models based on Sp confining supersymmetric QCD plus singlets according to their standard model index and number of composite messengers. Furthermore, this leads to simple, calculable models that spontaneously break supersymmetry, reproduce the fermion flavor hierarchy, and explain the standard model index dynamically with little or no additional matter. At low energies these theories realize a “more-minimal” soft spectrum with direct mediation and a gravitino lightest supersymmetric particle.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nearly Supersymmetric Dark Atoms

Theories of dark matter that support bound states are an intriguing possibility for the identity of the missing mass of the Universe. This article proposes a class of models of supersymmetric composite dark matter where the interactions with the Standard Model communicate supersymmetry breaking to the dark sector. In these models, supersymmetry breaking can be treated as a perturbation on the spectrum of bound states. Using a general formalism, the spectrum with leading supersymmetry effects is computed without specifying the details of the binding dynamics. The interactions of the composite states with the Standard Model are computed, and several benchmark models are described. General features of nonrelativistic supersymmetric bound states are emphasized.

Behbahani, Siavosh R.↗