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Raghavan Rangarajan

Publications and source records attributed to Raghavan Rangarajan.

43 records · Page 3Linked to original sources

Light-Gravitino Production at Hadron Colliders

We consider the production of gravitinos ($\widetilde G$) in association with gluinos ($\tilde g$) or squarks ($\tilde q$) at hadron colliders, including the three main sub-processes: $q \bar q -> \tilde g\widetilde G$, $qg -> \tilde q\widetilde G$, and $gg -> \tilde g\widetilde G$. These channels become enhanced to the point of being observable for sufficiently light gravitino masses ($m_{\widetilde G} < 10^{-4} eV$), as motivated by some supersymmetric explanations of the CDF $eeγγ+ E_{T,miss}$ event. The characteristic signal of such events would be monojets, as opposed to dijets obtained in the more traditional supersymmetric process $p \bar p -> \tilde g\tilde g$. Searches for such events at the Tevatron can impose lower limits on the gravitino mass. In the Appendix, we provide a complete set of Feynman rules for gravitino interactions used in our calculation.

hep-ph↗

New Supersymmetric Contributions to $t->cV$

We calculate the electroweak-like one-loop supersymmetric contributions to the rare and flavor-violating decay of the top quark into a charm quark and a gauge boson: $t->c V$, with $V=γ,Z,g$. We consider loops of both charginos and down-like squarks (where we identify and correct an error in the literature) and neutralinos and up-like squarks (which have not been calculated before). We also account for left-right and generational squark mixing. Our numerical results indicate that supersymmetric contributions to $t->cV$ can be upto 5 orders of magnitude larger than their Standard Model counterparts. However, they still fall short of the sensitivity expected at the next-generation top-quark factories.

hep-ph↗

Baryogenesis During Reheating in Natural Inflation and Comments on Spontaneous Baryogenesis

We calculate the baryon asymmetry created by the decay of a pseudo Nambu-Goldstone boson whose interactions violate baryon number conservation. Our results are in disagreement with previous results in the original spontaneous baryogenesis models for the asymmetry produced by the decay of an oscillating scalar field with B number violating derivative couplings; we find that the net baryon number density is proportional to $þ_i^3$, where $þ_i$ is the amplitude of the PNGB-field in natural inflation at the onset of reheating. We also discuss our disagreement with the interpretation of $\dotθ$ as an effective chemical potential for baryon number in spontaneous baryogenesis models. While our calculation of the asymmetry is carried out in the context of natural inflation our approach is generally valid for baryogenesis models using decaying classical fields. In the Appendices, we include a complete derivation of the number density of particles produced by the decay of a classical scalar field; this number density is proportional to the integral over momenta of the one pair production amplitude.

hep-ph↗

Cosmological Constraints on the Scale of Supersymmetry Breaking

We consider the cosmological and astrophysical constraints on the decay of massive $E_8 \times E_8^\prime$ superstring axions associated with the hidden sector. We find that decay lifetimes greater than 1 s are ruled out by limits from nucleosynthesis, by limits on the distortion of the cosmic microwave and gamma ray backgrounds and by closure arguments. We conclude that $Λ>1.2\times10^{13}\gev$, where $Λ$ is the scale of gaugino condensation in the hidden sector. This implies that the scale of supersymmetry breaking is greater than $10^{10}\gev$. Significantly, our result agrees with the value of $5\times 10^{13}\gev$ for $Ł$ obtained independently by setting supersymmetric scalar masses equal to $m_W$.

hep-ph↗

Constraints on Baryogenesis from the Decay of Superstring Axions

We calculate the dilution of the baryon-to-photon ratio by the decay of superstring axions. We find that the dilution is of the order of $10^7$. We review several models of baryogenesis and show that most of them can not tolerate such a large dilution. In particular, only one current model of electroweak baryogenesis possibly survives. The Affleck-Dine mechanism in SUSY GUTs is very robust and the dilution by axions could contribute to the dilution required in these models. Baryogenesis scenarios involving topological defects and black hole evaporation are also capable of producing a sufficiently large baryon asymmetry.

hep-ph↗

The Angular Dependence of the Three-Point Correlation Function of the Cosmic Microwave Background Radiation as Predicted by Inflationary Cosmologies

Inflationary models predict a definite, model independent, angular dependence for the three-point correlation function of $ΔT/T$ at large angles (greater than $\sim 1^\circ$) which we calculate. The overall amplitude is model dependent and generically unobservably small, but may be large in some specific models. We compare our results with other models of nongaussian fluctuations.

astro-ph↗

Dependence of Density Perturbations on the Coupling Constant in a Simple Model of Inflation

In the standard inflationary scenario with inflaton potential $V(Φ)=M^4-{1\over4}λΦ^4$, the resulting density perturbations $δρ/ρ$ are proportional to $λ^{1/2}$. Upper bounds on $δρ/ρ$ require $λ< 10^{-13}$. Ratra has shown that an alternative treatment of reheating results in $δρ/ρ\propto λ^{-1}$, so that an upper bound on $δρ/ρ$ does not put an obvious upper bound on $λ$. We verify that $δρ/ρ\propto λ^{-1}$ is indeed a possibility, but show that $λ< 10^{-13}$ is still required.

astro-ph↗