arXiv subjects

Vikram Rentala

Publications and source records attributed to Vikram Rentala.

25 records · Page 2Linked to original sources

arXiv2011

WIMPless Dark Matter in Anomaly-Mediated Supersymmetry Breaking with Hidden QED

In anomaly-mediated supersymmetry breaking, superpartners in a hidden sector have masses that are proportional to couplings squared, and so naturally freeze out with the desired dark matter relic density for a large range of masses. We present an extremely simple realization of this possibility, with WIMPless dark matter arising from a hidden sector that is supersymmetric QED with N_F flavors. Dark matter is multi-component, composed of hidden leptons and sleptons with masses anywhere from 10 GeV to 10 TeV, and hidden photons provide the thermal bath. The dark matter self-interacts through hidden sector Coulomb scatterings that are potentially observable. In addition, the hidden photon contribution to the number of relativistic degrees of freedom is in the range ΔN_eff ~ 0 - 2, and, if the hidden and visible sectors were initially in thermal contact, the model predicts ΔN_eff ~ 0.2 - 0.4. Data already taken by Planck may provide evidence of such deviations.

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arXiv2011

Simplified Models for LHC New Physics Searches

This document proposes a collection of simplified models relevant to the design of new-physics searches at the LHC and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the "Topologies for Early LHC Searches" workshop, held at SLAC in September of 2010, the purpose of which was to develop a set of representative models that can be used to cover all relevant phase space in experimental searches. Particular emphasis is placed on searches relevant for the first ~50-500 pb-1 of data and those motivated by supersymmetric models. This note largely summarizes material posted at http://lhcnewphysics.org/, which includes simplified model definitions, Monte Carlo material, and supporting contacts within the theory community. We also comment on future developments that may be useful as more data is gathered and analyzed by the experiments.

hep-ph↗

arXiv2011

A Simplified Model Approach to Same-sign Dilepton Resonances

We discuss same-sign dilepton resonances in the simplified model approach. The relevant $SU(3}_Q^J$ quantum numbers are $1_2^{0,1,2}$. For simplicity, we only consider a spin 0 scalar, which is typically referred to as a doubly charged Higgs in the literature. We consider the three simplest cases where the doubly charged Higgs resides in a singlet, doublet or triplet $SU(2)_L$ representation. We discuss production and decay of such a doubly charged Higgs, summarize the current direct search limits, and obtain mass limits in the cases of singlet and doublet for the first time. We also present a complete set of updated indirect search limits. We study the discovery potential at the Large Hadron Collider (LHC) with center of mass energies 7 and 14 TeV for the dominant Drell-Yan pair production with $H^{\pm\pm}$ decay in the $ee$ and $μμ$ channels. We find that at 7 TeV, the LHC with 10 $fb^{-1}$ luminosity can probe mass of the doubly charged Higgs up to 380 GeV assuming 100% decay to leptons. At 14 TeV, the LHC with 100 $fb^{-1}$ luminosity can reach a mass of up to 800 GeV.

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arXiv2010

Saving fourth generation and baryon number by living long

Recent studies of precision electroweak observables have led to the conclusion that a fourth generation is highly constrained. However, we point out that a long-lived fourth generation can reopen a large portion of the parameter space. In addition, it preserves baryon and lepton asymmetries against sphaleron erasure even if $B-L=0$. It opens up the possibility of exact $B-L$ symmetry and hence Dirac neutrinos. The fourth generation can be observed at the LHC with unique signatures of long-lived particles in the near future.

hep-ph↗

arXiv2009

Randall-Sundrum graviton spin determination using azimuthal angular dependence

Quantum interference of helicity amplitudes provides a powerful tool for measuring the spins of new particles. By looking at the azimuthal angular dependence of the differential cross-section in the production followed by decay of a new particle species one can determine its spin by looking at the various cosine modes. The heavy spin-2 Kaluza-Klein (KK) graviton provides a unique signature with a $\cos{(4 ϕ)}$ mode. We study the feasibility of this approach to measuring the spin of the KK graviton in the Randall-Sundrum Model at the LHC.

hep-ph↗

arXiv2009

Color Sextet Scalars at the CERN Large Hadron Collider

Taking a phenomenological approach, we study a color sextet scalar at the LHC. We focus on the QCD production of a color sextet pair Φ_6\barΦ_{6} through gg fusion and q\bar{q} annihilation. Its unique coupling to \bar{ψ^c}ψallows the color sextet scalar to decay into same-sign diquark states, such as Φ_6\to tt/tt^*. We propose a new reconstruction in the multijet plus same sign dilepton with missing transverse energy samples to search for on-shell tt\bar{t}\bar{t} final states from sextet scalar pair production. Thanks to the large QCD production, the search covers the sextet mass range up to 1 TeV for 100 fb^-1 integrated luminosity.

hep-ph↗

arXiv2008

Discriminating spin through quantum interference

Many of the proposed solutions to the hierarchy and naturalness problems postulate new `partner' fields to the standard model particles. Determining the spins of these new particles will be critical in distinguishing among the various possible SM extensions, yet proposed methods rely on the underlying models. We propose a new model-independent method for spin measurements which takes advantage of quantum interference among helicity states. We demonstrate that this method will be able to discriminate scalar particles from higher spin states at the ILC, and discuss application to higher spins and possible uses at the LHC.

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