Electroweak baryogenesis (EWBG) remains a theoretically attractive and experimentally testable scenario for explaining the cosmic baryon asymmetry We review recent progress in computations of the baryon asymmetry within this framework and discuss their phenomenological consequences We pay particular attention to methods for analyzing the electroweak phase transition and calculating CP-violating asymmetries, the development of Standard Model extensions that may provide the necessary ingredients for EWBG, and searches for corresponding signatures at the high energy, intensity, and cosmological frontiers

pdf/electroweak-baryogenesis-2lmb3v5ed4.pdf

Electroweak baryogenesis

The first 1 fb−1 of LHC searches have set impressive limits on new colored particles decaying to missing energy. We address the implication of these searches for naturalness in supersymmetry (SUSY). General bottom-up considerations of natural electroweak symmetry breaking show that higgsinos, stops, and the gluino should not be too far above the weak scale. The rest of the spectrum, including the squarks of the first two generations, can be heavier and beyond the current LHC reach. We have used collider simulations to determine the limits that all of the 1 fb−1 searches pose on higgsinos, stops, and the gluino. We find that stops and the left-handed sbottom are starting to be constrained and must be heavier than about 200–300 GeV when decaying to higgsinos. The gluino must be heavier than about 600–800 GeV when it decays to stops and sbottoms. While these findings point toward scenarios with a lighter third generation split from the other squarks, we do find that moderately-tuned regions remain, where the gluino is just above 1 TeV and all the squarks are degenerate and light. Among all the searches, jets plus missing energy and same-sign dileptons often provide the most powerful probes of natural SUSY. Overall, our results indicate that natural SUSY has survived the first 1 fb−1 of data. The LHC is now on the brink of exploring the most interesting region of SUSY parameter space.

Natural SUSY Endures

Motivated by the recent LHC hints of a Higgs boson around 125 GeV, we assume a SM-like Higgs with the mass 123-127 GeV and study its implication in low energy SUSY by comparing the MSSM and NMSSM. We consider various experimental constraints at 2 sigma level (including the muon g - 2 and the dark matter relic density) and perform a comprehensive scan over the parameter space of each model. Then in the parameter space which is allowed by current experimental constraints and also predicts a SM-like Higgs in 123-127 GeV, we examine the properties of the sensitive parameters (like the top squark mass and the trilinear coupling A(t)) and calculate the rates of the di-photon signal and the VV* (V = W, Z) signals at the LHC. Our typical findings are: (i) In the MSSM the top squark and A(t) must be large and thus incur some fine-tuning, which can be much ameliorated in the NMSSM; (ii) In the MSSM a light stau is needed to enhance the di-photon rate of the SM-like Higgs to exceed its SM prediction, while in the NMSSM the di-photon rate can be readily enhanced in several ways; (iii) In the MSSM the signal rates of pp -> h -> VV* at the LHC are never enhanced compared with their SM predictions, while in the NMSSM they may get enhanced significantly; (iv) A large part of the parameter space so far survived will be soon covered by the expected XENON100(2012) sensitivity (especially for the NMSSM).

A SM-like Higgs near 125 GeV in low energy SUSY: a comparative study for MSSM and NMSSM

Recent measurements of the cosmic microwave background (CMB) anisotropies by Planck provide a sensitive probe of dark matter annihilation during the cosmic dark ages, and specifically constrain the annihilation parameter ${f}_{\mathrm{eff}}⟨\ensuremath{\sigma}v⟩/{m}_{\ensuremath{\chi}}$. Using new results (paper II) for the ionization produced by particles injected at arbitrary energies, we calculate and provide ${f}_{\mathrm{eff}}$ values for photons and ${e}^{+}{e}^{\ensuremath{-}}$ pairs injected at keV-TeV energies; the ${f}_{\mathrm{eff}}$ value for any dark matter model can be obtained straightforwardly by weighting these results by the spectrum of annihilation products. This result allows the sensitive and robust constraints on dark matter annihilation presented by the Planck collaboration to be applied to arbitrary dark matter models with $s$-wave annihilation. We demonstrate the validity of this approach using principal component analysis. As an example, we integrate over the spectrum of annihilation products for a range of Standard Model final states to determine the CMB bounds on these models as a function of dark matter mass, and demonstrate that the new limits generically exclude models proposed to explain the observed high-energy rise in the cosmic ray positron fraction. We make our results publicly available at http://nebel.rc.fas.harvard.edu/epsilon.

Indirect dark matter signatures in the cosmic dark ages. I. Generalizing the bound on s-wave dark matter annihilation from Planck results

In this work, we examine the sensitivity of monojet searches at the LHC to directly produced charginos and neutralinos (electroweakinos) in the limit of small mass splitting, where the traditional multilepton plus missing energy searches loose their sen- sitivity. Werst recast the existing 8 TeV monojet search at CMS in terms of a SUSY simplied model with only light gauginos (winos and binos) or only light Higgsinos. The current searches are not sensitive to MSSM-like production cross sections, but would be sensitive to models with 2{20 times enhanced production cross section, for particle masses between 100 GeV and 250 GeV. Then we explore the sensitivity in the 14 TeV run of the LHC. Here we emphasise that in addition to the pure monojet search, soft leptons present in the samples can be used to increase the sensitivity. Exclusion of electroweakino masses up to 200 GeV is possible with 300 fb 1 at the LHC, if the systematic error can be reduced to the 1% level. Discovery is possible with 3000 fb 1 in some regions of parameter space.

/pdf/compressed-electroweakino-spectra-at-the-lhc-2c4xygjq4t.pdf

Compressed electroweakino spectra at the LHC

We employ the ATLAS search results for events containing jets and large missing transverse momentum, corresponding to an integrated luminosity of 1 fb^{-1}, to investigate the constrained minimal supersymmetric model (CMSSM) with b-\tau Yukawa coupling unification. In this scenario, one of the stops is the next-to-lightest supersymmetric particle (NLSP), which co-annihilates with the lightest (LSP) neutralino to yield the desired dark matter relic abundance. The NLSP stop, here taken to be lighter than the top quark, is slightly (<~ 20%-30%) heavier than the LSP neutralino, and it primarily decays into the LSP and a charm quark. We find that the multi-jets and monojet ATLAS searches are sensitive to this scenario if the stop pair production is accompanied by a hard QCD jet. The excluded limit for the NLSP stop mass from the ATLAS data can reach 160 GeV in the coannihilation region, with mass below 140 GeV essentially excluded. A significant region of the parameter space corresponding to large m_0 values, 8 TeV<~ m_0<~ 16 TeV, is excluded by our analysis. For LSP neutralino mass ~ 100 GeV, the LHC constraints in some cases on the spin-dependent (spin-independent) neutralino-nucleon cross section are significantly more stringent than the current and expected bounds from Xenon, CDMS and IceCube.

Stop-Neutralino Coannihilation in the Light of LHC

We explore the implications of 7 TeV LHC searches for a scenario in which one of the stops is the next-to-lightest supersymmetric particle (NLSP). The NLSP stop $ \left( {{{\tilde{t}}_1}} \right) $
 is assumed to decay exclusively into neutralino and charm quark. We consider processes where the stops are pair produced together with a hard QCD jet. We also consider stop quarks from gluino decays, $ \tilde{g} \to t\tilde{t}_1^{ * } + \bar{t}{\tilde{t}_1} $
 . We show that the monojet ATLAS and CMS searches corresponding to 1 fb−1 of integrated luminosity are sensitive to stop masses of up to 160 GeV, with the 20 % neutralino-stop coannihilation region essentially ruled out for $ {M_{{{{\tilde{t}}_1}}}}{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{ < }}140\,{\text{GeV}} $
 . The region $ {M_{{{{\tilde{t}}_1}}}}{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{ < }}130\,{\text{GeV}} $
 is excluded with even relatively larger mass difference, $ {M_{{{{\tilde{t}}_1}}}} - {M_{{\tilde{\chi }_1^0}}} \sim 40\,{\text{GeV}} $
 , by the multi-jets search. The b-jet and same-sign dilepton searches are sensitive to a heavier gluino because they only pick up gluino pair production events followed by top quarks decaying into b-jets and same-sign dileptons, respectively. We find that the LHC data places a lower limit on the gluino mass in this scenario of about 600 GeV (700 GeV) from b-jets (same-sign dileptons) searches.

Impact of LHC searches on NLSP top squark and gluino mass

We investigate the collider phenomenology of gluino-bino co-annihilation scenario both at the Tevatron and 7 TeV LHC. This scenario can be realized, for example, in a class of realistic supersymmetric models with non-universal gaugino masses and t − b−τ Yukawa unification. The NLSP gluino and LSP bino should be nearly degenerate in mass, so that the typical gluino search channels involving leptons or hard jets are not available. Consequently, the gluino can be lighter than various bounds on its mass from direct searches. We propose a new search for NLSP gluino involving multi-b final states, arising from the three-body decay $ \tilde{g} \to b\overline b \tilde{\chi }_1^0 $. We identify two realistic models with gluino mass of around 300 GeV for which the three-body decay is dominant, and show that a 4.5 σ observation sensitivity can be achieved at the Tevatron with an integrated luminosity of 10 fb−1. For the 7TeV LHC with 50 pb−1 of integrated luminosity, the number of signal events for the two models is $ \mathcal{O}\left( {10} \right) $, to be compared with negligible SM background events.

NLSP gluino search at the Tevatron and early LHC

We investigate the collider phenomenology of gluino-bino co-annihilation scenario both at the Tevatron and 7 TeV LHC. This scenario can be realized, for example, in a class of realistic supersymmetric models with non-universal gaugino masses and t-b-\tau Yukawa unification. The NLSP gluino and LSP bino should be nearly degenerate in mass, so that the typical gluino search channels involving leptons or hard jets are not available. Consequently, the gluino can be lighter than various bounds on its mass from direct searches. We propose a new search for NLSP gluino involving multi-b final states, arising from the three-body decay \tilde{g}-> b\bar{b}\tilde{\chi}_1^0. We identify two realistic models with gluino mass of around 300 GeV for which the three-body decay is dominant, and show that a 4.5 \sigma observation sensitivity can be achieved at the Tevatron with an integrated luminosity of 10 fb^{-1}. For the 7 TeV LHC with 50 pb^{-1} of integrated luminosity, the number of signal events for the two models is O(10), to be compared with negligible SM background event.

NLSP Gluino Search at the Tevatron and early LHC

We discuss an extended standard model electroweak sector which contains a stable scalar dark matter particle, the D boson. To search for the D boson at the LHC we exploit the flavor-changing neutral current top quark decay, t{yields}cDD, mediated by the lightest standard model-like Higgs h{sup 0} in a two Higgs doublet model framework. The branching ratio for t{yields}cDD in this case can be as high as 10{sup -3}, after taking into account constraints arising from the D boson relic abundance. With an integrated luminosity of 10(100) fb{sup -1}, the 14 TeV LHC can explore values of this branching ratio that are one (two) order of magnitude smaller in tt production with tt{yields}cbl{sup -}(cbl{sup +})+Ee{sub T}. For a D boson mass < or approx. 60 GeV, m{sub h}{sup 0} < or approx. 2M{sub Z}, 10 fb{sup -1} luminosity and a branching ratio BR(t{yields}cDD){approx}10{sup -4}, the estimated number of signal events at the 14 TeV LHC is of order 80.

Scalar dark matter search at the LHC through flavor-changing neutral current top decay

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