119883211
Conflicts between B-violating phenomena in supergravity models
Abstract We show that there is an incompatibility between matter stability and cosmological baryon production in standard N = 1 supergravity models. This discrepancy emerges from the bound on the reheating temperature T rh ⩽ 10 10 GeV which comes from the restriction on the gravitino decay after inflation. Some weird possibilities to bypass the controversy are also analyzed.
13291931
Hidden sector gaugino condensation and the model independent axion
Abstract In the effective field theory framework, we consider the effect of supersymmetry breaking via gaugino condensation and supergravity in the hidden sector gauge group on the hidden sector vacuum angle θ h . The θ h parameter dependence of the potential yields phenomenologically acceptable invisible axion solutions if the U (1) R symmetry is broken down to a discrete subgroup Z N with N ≥3 ( N =4 is marginal). Anomalous U(1) superstring models are good candidates for this invisible axion resolution of the strong CP puzzle.
14469939
Z12−I Orbifold Compactification toward SUSY Standard Model
We explain the orbifold compactification in string models and present a Z12−I orbifold compactification toward supersymmetric standard models. We also point out an effective R-parity from this string construction. The VEVs of gauge singlets are chosen such that phenomenological constraints are satisfied.
121621613
Fractionally charged lepton and low-mass magnetic monopole
We study an SO(14) model to obtain a low-mass magnetic monopole and fractionally charged leptons. The mass of the magnetic monopole is roughly-equal2 x 10/sup 9/ GeV.
11881623
Neutrino mass and lepton number violation with charged scalars
If there exist only three light neutrinos below the weak scale, the neutrino masses can arise by breaking the lepton number L. One example is the Zee mechanism for the neutrino masses. We study phenomenological implications of neutrino masses arising from the L violation through introduction of SU(2) X U(1) singlet scalars with Q_{em}=1 and 2.
122080712
Natural mass scale and neutrino oscillation
Two principles, the standard SU(2)/sub L/ x U(1) electroweak theory below 100 GeV and the natural mass scale, are suggested for studying possible connections between neutrino oscillation and a mass hierarchy above 100 GeV. Neutrino-oscillation parameters of order or approx. = 10/sup 8/--10/sup 9/ GeV. An SU(7) model in this scenario is described in some detail.
118704767
First LHC Constraints on Neutralinos
Abstract The ATLAS and CMS Collaborations have recently reported tantalizing hints of the existence of a 125 GeV Higgs-like particle, whose couplings appear to match well the Standard Model (SM) expectations. In this work, we study implications of this observation for the neutralino sector of supersymmetric models, assuming that the Higgs signal gets confirmed. In general, the Higgs decay into neutralinos can be one of its dominant decay channels. Since a large invisible Higgs decay branching ratio would be in conflict with the data, this possibility is now constrained. In particular, we find that most of the region μ 170 GeV , M 1 70 GeV at tan β ∼ 10 and μ 120 GeV , M 1 70 GeV at tan β ∼ 40 is disfavored.
14834509
Electroweak Contributions to Squark Pair Production
We compute electroweak contributions to the production of squark pairs at hadron colliders. These include the exchange of electroweak gauge bosons in the $s-$channel as well as electroweak gaugino exchange in the $t-$ and/or $u-$channel. In many cases these can interfere with the dominant QCD contributions. As a result, we find sizable contributions to the production of two SU(2) doublet squarks. At the LHC, they amount to 10 to 20% for typical mSUGRA (or CMSSM) scenarios, but in more general scenarios they can vary between -40 and $+55%$, depending on size and sign of the SU(2) gaugino mass. The electroweak contribution to the total squark pair production rate at the LHC is about 3.5 times smaller.
118452202
Understanding the WMAP Cold Spot mystery
The Cold Spot (CS) at galactic coordinates (b = −57°, l = 209°) was discovered in the Wilkinson Microwave Anisotropy Probe (WMAP)data as a cosmic background anomaly. In order to assess the cosmological significance of the Spot, we examine its properties using the cluster analysis of the local extrema in the cosmic microwave background (CMB) signal. We also check the hypothesis that the CMB signal has a non-Gaussian tail, localized in the low-multipole components. We constructed a linear filter, dividing the signal into two parts: non-Gaussian and Gaussian. Using the filter scale as a variable, we can maximize the skewness and kurtosis of the smoothed signal and minimize these statistics. We discovered that the shape of the CS is formed primarily by the components of the CMB signal represented by the multipoles between 10 ≤ ℓ ≤ 20, with a corresponding angular scale of about 5°–10°. This signal leads to the modulation of the CMB on the whole sky, clearly seen at |b| > 30° in both the ILC andWCM maps, rather than in a single localized feature. After subtraction of this modulation, the remaining part of the CMB signal appears to be consistent with statistical homogeneity and Gaussianity. We therefore infer that the mystery of the WMAP Cold Spot reflects directly the peculiarities of low multipoles of the CMB signal, rather than a single local (isolated) defect or the manifestations of a globally anisotropic cosmology.
53370252
Positroid stratification of orthogonal Grassmannian and ABJM amplitudes
A bstractA novel understanding of scattering amplitudes in terms of on-shell diagrams and positive Grassmannian has been recently established for four dimensional Yang-Mills theories and three dimensional Chern-Simons theories of ABJM type. We give a detailed construction of the positroid stratification of orthogonal Grassmannian relevant for ABJM amplitudes. On-shell diagrams are classified by pairing of external particles. We introduce a combinatorial aid called ‘OG tableaux’ and map each equivalence class of on-shell diagrams to a unique tableau. The on-shell diagrams related to each other through BCFW bridging are naturally grouped by the OG tableaux. Introducing suitably ordered BCFW bridges and positive coordinates, we construct the complete coordinate charts to cover the entire positive orthogonal Grassmannian for arbitrary number of external particles. The graded counting of OG tableaux suggests that the positive orthogonal Grassmannian constitutes a combinatorial polytope.
119172488
Light Stop Searches at the LHC in Events with two b-Jets and Missing Energy
We propose a new method to discover light top squarks (stops) in the co-annihilation region at the Large Hadron Collider (LHC). The bino-like neutralino is the lightest supersymmetric particle (LSP) and the lighter stop is the next-to-LSP. Such scenarios can be consistent with electroweak baryogenesis and also with dark matter constraints. We consider the production of two stops in association with two b-quarks, including pure QCD as well as mixed electroweak-QCD contributions. The stops decay into a charm quark and the LSP. For a higgsino-like light chargino, the electroweak contributions can exceed the pure QCD prediction. We show the size of the electroweak contributions as a function of the stop mass and present the LHC discovery reach in the stop-neutralino mass plane.