arXiv subjects

Hasan Serce

Publications and source records attributed to Hasan Serce.

22 records · Page 2Linked to original sources

arXiv2015

Supersymmetry with radiatively-driven naturalness: implications for WIMP and axion searches

By insisting on naturalness in both the electroweak and QCD sectors of the MSSM, the portrait for dark matter production is seriously modified from the usual WIMP miracle picture. In SUSY models with radiatively-driven naturalness (radiative natural SUSY or RNS) which include a DFSZ-like solution to the strong CP and SUSY mu problems, dark matter is expected to be an admixture of both axions and higgsino-like WIMPs. The WIMP/axion abundance calculation requires simultaneous solution of a set of coupled Boltzmann equations which describe quasi-stable axinos and saxions. In most of parameter space, axions make up the dominant contribution of dark matter although regions of WIMP dominance also occur. We show the allowed range of PQ scale f_a and compare to the values expected to be probed by the ADMX axion detector in the near future. We also show WIMP detection rates which are suppressed from usual expectations because now WIMPs comprise only a fraction of the total dark matter. Nonetheless, ton-scale noble liquid detectors should be able to probe the entirety of RNS parameter space. Indirect WIMP detection rates are less propitious since they are reduced by the square of the depleted WIMP abundance.

hep-ph↗

arXiv2015

Coupled Boltzmann computation of mixed axion neutralino dark matter in the SUSY DFSZ axion model

The supersymmetrized DFSZ axion model is highly motivated not only because it offers solutions to both the gauge hierarchy and strong CP problems, but also because it provides a solution to the SUSY mu problem which naturally allows for a Little Hierarchy. We compute the expected mixed axion-neutralino dark matter abundance for the SUSY DFSZ axion model in two benchmark cases-- a natural SUSY model with a standard neutralino underabundance (SUA) and an mSUGRA/CMSSM model with a standard overabundance (SOA). Our computation implements coupled Boltzmann equations which track the radiation density along with neutralino, axion (produced thermally (TH) and via coherent oscillations (CO)), saxion (TH- and CO-produced), axino and gravitino densities. In the SUSY DFSZ model, axions, axinos and saxions go through the process of freeze-in-- in contrast to freeze-out or out-of-equilibrium production as in the SUSY KSVZ model-- resulting in thermal yields which are largely independent of the re-heat temperature. We find the SUA case with suppressed saxion-axion couplings (ξ=0) only admits solutions for PQ breaking scale f_a~< 5\times 10^{12} GeV where the bulk of parameter space tends to be axion-dominated. For SUA with allowed saxion-axion couplings (ξ=1), then f_a values up to ~ 2\times 10^{14} GeV are allowed. For the SOA case, almost all of SUSY DFSZ parameter space is disallowed by a combination of overproduction of dark matter, overproduction of dark radiation or violation of BBN constraints. An exception occurs at very large f_a~ 10^{15}-10^{16} GeV where large entropy dilution from CO-produced saxions leads to allowed models.

hep-ph↗

arXiv2015

Mixed axion-wino dark matter

A variety of supersymmetric models give rise to a split mass spectrum characterized by very heavy scalars but sub-TeV gauginos, usually with a wino-like LSP. Such models predict a thermally-produced underabundance of wino-like WIMP dark matter so that non-thermal DM production mechanisms are necessary. We examine the case where theories with a wino-like LSP are augmented by a Peccei-Quinn sector including an axion-axino-saxion supermultiplet in either the SUSY KSVZ or SUSY DFSZ models and with/without saxion decays to axions/axinos. We show allowed ranges of PQ breaking scale f_a for various cases which are generated by solving the necessary coupled Boltzmann equations. We also present results for a model with radiatively-driven naturalness but with a wino-like LSP.

hep-ph↗

arXiv2014

A natural Little Hierarchy for SUSY from radiative breaking of PQ symmetry

While LHC8 Higgs mass and sparticle search constraints favor a multi-TeV value of gravitino mass m_{3/2}, electroweak naturalness favors a superpotential higgsino mass μ~100-200 GeV: the mis-match results in an apparent Little Hierarchy characterized by μ<< m_{3/2}. It has been suggested that the Little Hierarchy arises from a mis-match between Peccei-Quinn (PQ) and hidden sector intermediate scales v_{PQ}<< m_{\rm hidden}. We examine the Murayama-Suzuki-Yanagida (MSY) model of radiatively-driven PQ symmetry breaking which not only generates a weak scale value of μbut also produces intermediate scale Majorana masses for right-hand neutrinos. For this model, we show ranges of parameter choices with multi-TeV values of m_{3/2} which can easily generate values of μ~100-200 GeV so that the apparent Little Hierarchy suggested from data emerges quite naturally. In such a scenario, dark matter would be comprised of an axion plus a higgsino-like WIMP admixture where the axion mass and higgsino masses are linked by the value of the PQ scale. The required light higgsinos should ultimately be detected at a linear e^+e^- collider with \sqrt{s}>2m({\rm higgsino}).

hep-ph↗