15721073
Gauge unification via stable brane recombination
We study the transition between parallel and intersecting branes on a torus. Spontaneous symmetry breaking of nonabelian gauge symmetry is understood as brane separation, and a more general intermediate deformation is discussed. We argue that there exists supersymmetry preserving transition and we can always have parallel branes as a final state. The transition is interpreted due to dynamics of the F- and D-string junctions and their generalization to (F, Dp) bound states. The gauge group and coupling unification is achieved, also as a result of supersymmetry. From the tadpole cancelation condition, we naturally have intersecting brane models as broken phases of type-I theory with SO(32) gauge group.
16283086
Three generation magnetized orbifold models
Abstract We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N = 1 super-Yang–Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown.
2520502
String compactification, QCD axion and axion–photon–photon coupling
It is pointed out that there exist a few problems to be overcome toward an observable sub-eV QCD axion in superstring compactification. We give a general expression for the axion decay constant. For a large domain wall number NDW, the axion decay constant can be substantially lowered from a generic value of a scalar singlet VEV. The Yukawa coupling structure in the recent Z12?I model is studied completely, including the needed nonrenormalizable terms toward realistic quark and lepton masses. In this model we find an approximate global symmetry and vacuum so that a QCD axion results but its decay constant is at the GUT scale. The axion?photon?photon coupling is calculated with a reasonable assumption on a realistic vacuum satisfying the quark and lepton mass matrix conditions. It is the first time calculation of ca?? in realistic string compactifications: ca?? = 5/3?1.93 ?0.26.
118042770
SU(3) x SU(2) x U(1) Vacua in F-Theory
The Standard Model group and matter spectrum is obtained in vacua of F-theory, without resorting to an intermediate unification group. The group SU(3) x SU(2) x U(1)_Y is the commutant to SU(5)_t \times U(1)_Y structure group of a Higgs bundle in E_8 and is geometrically realized as a deformation of I_5 singularity. Lying along the unification groups of E_n, our vacua naturally inherit their unification structure. By modding SU(5)_t out by Z_4 monodromy group, we can distinguish Higgses from lepton doublets by matter parity. Turning on universal G-flux on this part, the spectrum contains three generations of quarks and leptons, as well as vectorlike pairs of electroweak and colored Higgses. Minimal Yukawa couplings is obtained at the renormalizable level.
118554240
Contorted flavors in grand unification and proton decay
Abstract Conventionally we collect electron and up/down quarks ( u , d ) ⊕ ( ν e , e ) to form unified generations, and collect the left-handed and the right-handed fermions of the same flavors ( ν e , e ) ⊕ e ¯ . We can alternatively have a contorted multiplet, made by pairing different quarks and leptons, like ( u , d ) ⊕ ( ν μ , μ ) or ( u , d ) ⊕ ( ν τ , τ ) , and/or between different left- and right-handed fermions to ( ν e , e ) ⊕ μ ¯ , etc. These can suppress proton decay, due to its high flavor dependence, while having the correct fermion masses.
119201914
Extended gauge symmetries in F-theory
We study gauge symmetry in F-theory in light of global aspects. For this, we consider not only a simple (local) group, but also a semi-simple group with Abelian factors. Once we specify the complete gauge group by decomposing the discriminant, analogous to arranging 7-branes, we can derive the matter contents, their localization and the relation to enhanced groups. Global constraints coming from Calabi-Yau conditions and anomaly cancellations imply a unified group. The semisiple group shows explicit formation of matter curves and nontriviality of its embedding into exceptional group. Also the dual heterotic string vacua with line bundles provide a guide on the unification.
53454258
Reducing combinatorial uncertainties: a new technique based on MT2 variables
A bstractWe propose a new method to resolve combinatorial ambiguities in hadron collider events involving two invisible particles in the final state. This method is based on the kinematic variable MT 2 and on the MT 2-assisted-on-shell reconstruction of invisible momenta, that are reformulated as ‘test’ variables Ti of the correct combination against the incorrect ones. We show how the efficiency of the single Ti in providing the correct answer can be systematically improved by combining the different Ti and/or by introducing cuts on suitable, combination-insensitive kinematic variables. We illustrate our whole approach in the specific example of top anti-top production, followed by a leptonic decay of the W on both sides. However, by construction, our method is also directly applicable to many topologies of interest for new physics, in particular events producing a pair of undetected particles, that are potential dark-matter candidates. We finally emphasize that our method is apt to several generalizations, that we outline in the last sections of the paper.
118129565
Axial properties of the nucleon and N* resonances
We report results from a theoretical study of axial charges and axial form factors of the nucleon N and its resonant states N*. By employing relativistic constituent-quark models we could produce for the first time covariant predictions for the axial-current matrix elements. The calculations are performed in the point form of Poincare-invariant quantum mechanics. The axial charge as well as the axial form factor of the nucleon are reproduced close to phenomenology. The axial charges of the N*(1535) and N*(1650) resonances – the only cases where such a comparison is possible – agree well with results from quantum chromodynamics on the lattice that have recently become available. Here, we present the axial charges of all N* excitations below ~2 GeV and two examples of N* axial form factors. These results should be interesting for comparison with other approaches, especially with regard to the issue of chiral-symmetry restoration in higher-lying hadron resonances.
53338971
Mixed mediation of supersymmetry breaking with anomalous U(1) gauge symmetry
Models with anomalous U(1) gauge symmetry contain various superfields which can have nonzero supersymmetry breaking auxiliary components providing the origin of soft terms in the visible sector, e.g. the U(1) vector superfield, the modulus or dilaton superfield implementing the Green-Schwarz anomaly cancellation mechanism, U(1)-charged but standard model singlet matter superfield required to cancel the Fayet-Iliopoulos term, and finally the supergravity multiplet. We examine the relative strength between these supersymmetry breaking components in a simple class of models, and find that various different mixed mediations of supersymmetry breaking, involving the modulus, gauge, anomaly and D-term mediations, can be realized depending upon the characteristics of D-flat directions and how those D-flat directions are stabilized with a vanishing cosmological constant. We identify two parameters which represent such properties and thus characterize how the various mediations are mixed. We also discuss the moduli stabilization and soft terms in a variant of KKLT scenario, in which the visible sector Kähler modulus is stabilized by the D-term potential of anomalous U(1) gauge symmetry.
119286463
Peccei-Quinn NMSSM in the light of 125 GeV Higgs
A bstractWe study the phenomenology of the Peccei-Quinn invariant extension of the next-to-minimal supersymmetric standard model (NMSSM) in view of the recent discovery of a 125 GeV Higgs boson. The minimal model having no quadratic and cubic terms of the NMSSM singlet field predicts a light singlino-like lightest supersymmetric particle (LSP). The model is strongly constrained by the Higgs invisible decay and the dark matter characteristic of the LSP, while some constraints can be relaxed by assuming that the saxion, the CP-even companion of the axion in the Peccei-Quinn sector, causes a late-time entropy production diluting the thermal LSP density. The collider signal of the model contains multi-jet and h/W/Z plus missing energy, which can be discovered in the early stage of the 14 TeV LHC running.
118444511
Indirect detection of gravitino dark matter including its three-body decays
It was recently pointed out that in supersymmetric scenarios with gravitino dark matter and bilinear R-parity violation, gravitinos with masses below MW typically decay with a sizable branching ratio into the 3-body final states W*? and Z*?. In this paper we study the indirect detection signatures of gravitino dark matter including such final states. First, we obtain the gamma ray spectrum from gravitino decays, which features a monochromatic contribution from the decay into ?? and a continuum contribution from the three-body decays. After studying its dependence on supersymmetric parameters, we compute the expected gamma ray fluxes and derive new constraints, from recent FERMI data, on the R-parity breaking parameter and on the gravitino lifetime. Indirect detection via antimatter searches, a new possibility brought about by the three-body final states, is also analyzed. For models compatible with the gamma ray observations, the positron signal is found to be negligible whereas the antiproton one can be significant.