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.
118237829
UV Completion of Axion
A multiple number of global U(1)s, arising from accidental symmetries up to a certain order of the potential, enjoy lowering the axion decay constant from UV‐scale and evading supersymmetric Fayet–Illiopoulos term constraints.
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.
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.
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.
119243457
Non-Abelian Discrete Flavor Symmetries on Orbifolds
We study non-Abelian flavor symmetries on orbifolds, S1/Z2 and T2/Z3. Our extra dimensional models realize DN, Σ(2N2), Δ(3N2) and Δ(6N2) including A4 and S4. In addition, one can also realize their subgroups such as QN, T7, etc. The S3 flavor symmetry can be realized on both S1/Z2 and T2/Z3 orbifolds.
18667052
A re-analysis of gravitino dark matter in the constrained MSSM
We re-consider the gravitino as dark matter in the framework of the Constrained MSSM. We include several recently suggested improvements on: (i) the thermal production of gravitinos, (ii) the calculation of the hadronic spectrum from NLSP decay and (iii) the BBN calculation including stau bound-state effects. In most cases we find an upper bound on the reheating temperature TR a few × 107GeV from over-production of 6Li from bound state effects. We also find an upper limit on the stau lifetime of 3 × 104sec, which is nearly an order of magnitude larger than the simple limit 5 × 103sec often used to avoid the effect of bound-state catalysis. The bound on TR is relaxed to a few × 108GeV when we use a more conservative bound on 6Li/7Li, in which case a new region at small stau mass at ~ 100GeV and much longer lifetimes opens up. Such a low stau mass region can be easily tested at the LHC.
9926808
Towards 5D Grand Unification without SUSY Flavor Problem
We consider the renormalization group approach to the SUSY flavor problem in the supersymmetric SU(5) model with one extra dimension. In higher dimensional SUSY gauge theories, it has been recently shown that power corrections due to Kaluza-Klein states of gauge fields run the soft masses generated at the orbifold fixed point to flavor conserving values in the infra-red limit. In models with GUT breaking at the brane where the GUT scale can be larger than the compactification scale, we show that the addition of a bulk Higgs multiplet, which is necessary for the successful unification, is compatible with the flavor universality achieved at the compactification scale.
92983543
Dark matter, {mu} problem, and neutrino mass with gauged R symmetry
We show that the {mu} problem and the strong CP problem can be resolved in the context of the gauged U(1){sub R} symmetry, realizing an automatic Peccei-Quinn symmetry. In this scheme, right-handed neutrinos can be introduced to explain small Majorana or Dirac neutrino mass. The U(1){sub R} D-term mediated supersymmetry (SUSY) breaking, called the U(1){sub R} mediation, gives rise to a specific form of the flavor-conserving superpartner masses. For the given solution to the {mu} problem, electroweak symmetry breaking condition requires the superpartners of the standard model at low energy to be much heavier than the gravitino. Thus, the dark matter candidate can be either gravitino or right-handed sneutrino. In the Majorana neutrino case, only gravitino is a natural dark matter candidate. On the other hand, in the Dirac neutrino case, the right-handed sneutrino can be also a dark matter candidate as it gets mass only from SUSY breaking. We discuss the non-thermal production of our dark matter candidates from the late decay of stau and find that the constraints from the big bang nucleosynthesis can be evaded for a TeV-scale stau mass.
118609463
Implications of an astrophysical interpretation of PAMELA and Fermi-LAT data for future searches of a positron signal from dark matter annihilations
The recent data from PAMELA and Fermi-LAT can be interpreted as evidence of new astrophysical sources of high energy positrons. In that case, such astrophysical positrons constitute an additional background against the positrons from dark matter annihilation. In this paper, we study the effect of that background on the prospects for the detection of a positron dark matter signal in future experiments. In particular, we determine the new regions in the (mass, $⟨\ensuremath{\sigma}v⟩$) plane that are detectable by the AMS-02 experiment for several dark matter scenarios and different propagation models. We find that, due to the increased background, these regions feature annihilation rates that are up to a factor of 3 larger than those obtained for the conventional background. That is, an astrophysical interpretation of the present data by PAMELA and Fermi-LAT implies that the detection of positrons from dark matter annihilation is slightly more challenging than previously believed.
8739021
Evolution of the curvature perturbation during and after multi-field inflation
We study the evolution of the curvature perturbation on the super-horizon scales starting from the inflationary epoch until there remains only a single dynamical degree of freedom, presureless matter, in the universe. We consider the cosmic inflation driven by a multiple number of the inflaton fields, which decay into both radiation and pressureless matter components. We present a complete set of the exact background and perturbation equations which describe the evolution of the universe throughout its history. By applying these equations to the simple but reasonable model of multi-field chaotic inflation, we explicitly show that the total curvature perturbation is continuously varying because of the non-adiabatic components of the curvature perturbation generated by the multiple