Reconciling thermal leptogenesis with the gravitino problem in SUSY models with mixed axion/axino dark matter

Successful implementation of thermal leptogenesis requires re-heat temperatures T_R\agt 2\times 10^9 GeV, in apparent conflict with SUSY models with TeV-scale gravitinos, which require much lower T_R in order to avoid Big Bang Nucleosynthesis (BBN) constraints. We show that mixed axion/axino dark matter can reconcile thermal leptogenesis with the gravitino problem in models with m_{\tG}\agt 30 TeV, a rather high Peccei-Quinn breaking scale and an initial mis-alignment angle \theta_i < 1. We calculate axion and axino dark matter production from four sources, and impose BBN constraints on long-lived gravitinos and neutralinos. Moreover, we discuss several SUSY models which naturally have gravitino masses of the order of tens of TeV. We find a reconciliation difficult in Yukawa-unified SUSY and in AMSB with a wino-like lightest neutralino. However, T_R\sim 10^{10}-10^{12} GeV can easily be achieved in effective SUSY and in models based on mixed moduli-anomaly mediation. Consequences of this scenario include: 1. an LHC SUSY discovery should be consistent with SUSY models with a large gravitino mass, 2. an apparent neutralino relic abundance \Omega_{\tz_1}h^2\alt 1, 3. no WIMP direct or indirect detection signals should be found, and 4. the axion mass should be less than \sim 10^{-6} eV, somewhat below the conventional range which is explored by microwave cavity axion detection experiments.Comment: 25 pages including 15 .eps figures; updated version to coincide with published versio

Thermal leptogenesis and the gravitino problem in the Asaka-Yanagida axion/axino dark matter scenario

A successful implementation of thermal leptogenesis requires the re-heat temperature after inflation T_R to exceed ~2\times 10^9 GeV. Such a high T_R value typically leads to an overproduction of gravitinos in the early universe, which will cause conflicts, mainly with BBN constraints. Asaka and Yanagida (AY) have proposed that these two issues can be reconciled in the context of the Peccei-Quinn augmented MSSM (PQMSSM) if one adopts a mass hierarchy m(sparticle)>m(gravitino)>m(axino), with m(axino) keV. We calculate the relic abundance of mixed axion/axino dark matter in the AY scenario, and investigate under what conditions a value of T_R sufficient for thermal leptogenesis can be generated. A high value of PQ breaking scale f_a is needed to suppress overproduction of axinos, while a small vacuum misalignment angle \theta_i is needed to suppress overproduction of axions. The large value of f_a results in late decaying neutralinos. To avoid BBN constraints, the AY scenario requires a low thermal abundance of neutralinos and high values of neutralino mass. We include entropy production from late decaying saxions, and find the saxion needs to be typically at least several times heavier than the gravitino. A viable AY scenario suggests that LHC should discover a spectrum of SUSY particles consistent with weak scale supergravity; that the apparent neutralino abundance is low; that a possible axion detection signal (probably with m_axion in the sub-micro-eV range) should occur, but no direct or indirect signals for WIMP dark matter should be observed.Comment: 28 pages including 21 .eps figures; high resolution pdf version available at http://www.nhn.ou.edu/~bae

Discovery potential for SUSY at a high luminosity upgrade of LHC14

After completion of the LHC8 run in 2012, the plan is to upgrade the LHC for operation close to its design energy sqrt{s}=14 TeV, with a goal of collecting hundreds of fb^{-1} of integrated luminosity. The time is propitious to begin thinking of what is gained by even further LHC upgrades. In this report, we compute an LHC14 reach for SUSY in the mSUGRA/CMSSM model with an anticipated high luminosity upgrade. We find that LHC14 with 300 (3000) fb^{-1} has a reach for SUSY via gluino/squark searches of m(gluino)\sim3.2 TeV (3.6 TeV) for m(squark)\sim m)gluino), and a reach of m(gluino)\sim1.8 TeV (2.3 TeV) for m(squark)>> m(gluino). In the case where m(squark)>> m(gluino), then the LHC14 reach for chargino-neutralino production with decay into the Wh+MET final state reaches to m(gluino)\sim2.6 TeV for 3000 fb^{-1}.Comment: 9 pages with 4 .eps figure

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.Comment: 25 pages including 14 .png figure

Wh plus missing-E_T signature from gaugino pair production at the LHC

In SUSY models with heavy squarks and gaugino mass unification, the gaugino pair production reaction pp-> \tw_1^\pm\tz_2 dominates gluino pair production for m_{\tg}\agt 1 TeV at LHC with \sqrt{s}=14 TeV (LHC14). For this mass range, the two-body decays \tw_1\to W\tz_1 and \tz_2\to h\tz_1 are expected to dominate the chargino and neutralino branching fractions. By searching for \ell b\bar{b}+MET events from \tw_1^\pm\tz_2 production, we show that LHC14 with 100 fb^{-1} of integrated luminosity becomes sensitive to chargino masses in the range m_{\tw_1}\sim 450-550 GeV corresponding to m_{\tg}\sim 1.5-2 TeV in models with gaugino mass unification. For 10^3 fb^{-1}, LHC14 is sensitive to the Wh channel for m_{\tw_1}\sim 300-800 GeV, corresponding to m_{\tg}\sim 1-2.8 TeV, which is comparable to the reach for gluino pair production followed by cascade decays. The Wh+MET search channel opens up a new complementary avenue for SUSY searches at LHC, and serves to point to SUSY as the origin of any new physics discovered via multijet and multilepton + MET channels.Comment: 5 pages with 4 .eps figure

Dark Matter Constraints on Composite Higgs Models

In composite Higgs models the pseudo-Nambu-Goldstone Boson (pNGB) nature of the Higgs field is an interesting alternative for explaning the smallness of the electroweak scale with respect to the beyond the Standard Model scale. In non-minimal models additional pNGB states are present and can be a Dark Matter (DM) candidate, if there is an approximate symmetry suppressing their decay. Here we assume that the low energy effective theory (for scales much below the compositeness scale) corresponds to the Standard Model with a pNGB Higgs doublet and a pNGB DM multiplet. We derive general effective DM Lagrangians for several possible DM representations (under the SM gauge group), including the singlet, doublet and triplet cases. Within this framework we discuss how the DM observables (relic abundance, direct and indirect detection) constrain the dimension-6 operators induced by the strong sector assuming that DM behaves as a Weakly Interacting Particle (WIMP) and that the relic abundance is settled through the freeze-out mechanism. We also apply our general results to two specific cosets: $SO(6)/SO(5)$ and $SO(6)/SO(4) \times SO(2)$, which contain a singlet and doublet DM candidate, respectively. In particular we show that if compositeness is a solution to the little hierarchy problem, representations larger than the triplet are strongly disfavored. Furthermore, we find that composite models can have viable DM candidates with much smaller direct detection cross-sections than their non-composite counterparts, making DM detection much more challenging.Comment: version accepted by JHE

Effective Supersymmetry at the LHC

We investigate the phenomenology of Effective Supersymmetry (ESUSY) models wherein electroweak gauginos and third generation scalars have masses up to about 1~TeV while first and second generation scalars lie in the multi-TeV range. Such models ameliorate the SUSY flavor and CP problems via a decoupling solution, while at the same time maintaining naturalness. In our analysis, we assume independent GUT scale mass parameters for third and first/second generation scalars and for the Higgs scalars, in addition to m_{1/2}, \tan\beta and A_0, and require radiative electroweak symmetry breaking as usual. We analyse the parameter space which is consistent with current constraints, by means of a Markov Chain Monte Carlo scan. The lightest MSSM particle (LMP) is mostly, but not always the lightest neutralino, and moreover, the thermal relic density of the neutralino LMP is frequently very large. These models may phenomenologically be perfectly viable if the LMP before nucleosynthesis decays into the axino plus SM particles. Dark matter is then an axion/axino mixture. At the LHC, the most important production mechanisms are gluino production (for m_{1/2} ~<700~GeV) and third generation squark production, while SUSY events rich in b-jets are the hallmark of the ESUSY scenario. We present a set of ESUSY benchmark points with characteristic features and discuss their LHC phenomenology.Comment: 26 pages including 13 figure