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.
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.
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.
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.
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.
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.
118998046
Flavor analysis of nucleon electromagnetic form factors
We have performed an evaluation of the individual up- and down-flavor contributions to the nucleon electromagnetic form factors within a relativistic constituent-quark model. It is found that the theoretical parameter-free predictions agree surprisingly well with recent experimental data from a flavor decomposition of the proton and neutron electromagnetic form factors for momentum transfers up to $Q^2\sim\;$3.5 GeV$^2$. It means that in this regime three-quark valence degrees of freedom dominate and other contributions, such as explicit mesonic effects, can at most play a minor role.
118380497
Gravitino Lightest Supersymmetric Particle as Dark Matter in the Constrained Minimal Supersymmetric Standard Model
In this talk, I present the possibility of gravitino lightest supersymmetric particle (LSP) as the dark matter in the framework of the Constrained MSSM. We find the prospects of the gravitino LSP for the implication on the vacuum structure of our universe and the solutions to the cosmic lithium problems.
2662233
Determining reheating temperature at colliders with axino or gravitino dark matter
After a period of inflationary expansion, the Universe reheated and reached full thermal equilibrium at the reheating temperature TR. In this work we point out that, in the context of effective low-energy supersymmetric models, LHC measurements may allow one to determine TR as a function of the mass of the dark matter particle assumed to be either an axino or a gravitino. An upper bound on their mass and on TR may also be derived.
119212917
Natural inflation with multiple sub-Planckian axions
We extend the Kim-Nilles-Peloso (KNP) alignment mechanism for natural inflation to models with $N>2$ axions, which obtains a super-Planckian effective axion decay constant $f_{\textrm{eff}}\gg M_{Pl}$ through an alignment of the anomaly coefficients of multiple axions having sub-Planckian fundamental decay constants $f_0\ll M_{Pl}$. The original version of the KNP mechanism realized with two axions requires that some of the anomaly coefficients should be of the order of $f_{\textrm{eff}}/f_0$, which would be uncomfortably large if $f_{\rm eff}/f_0 \gtrsim {\cal O}(100)$ as suggested by the recent BICEP2 results. We note that the KNP mechanism can be realized with the anomaly coefficients of $\mathcal{O}(1)$ if the number of axions $N$ is large as $N\ln N\gtrsim 2\ln (f_{\textrm{eff}}/f_0)$, in which case the effective decay constant can be enhanced as $f_{\rm eff}/f_0 \sim \sqrt{N !}\,n^{N-1}$ for $n$ denoting the typical size of the integer-valued anomaly coefficients. Comparing to the other multiple axion scenario, the N-flation scenario which requires $N \sim f_{\textrm{eff}}^2/f_0^2$, the KNP mechanism has a virtue of not invoking to a too large number of axions, although it requires a specific alignment of the anomaly coefficients, which can be achieved with a probability of ${\cal O}(f_0/f_{\rm eff})$ under a random choice of the anomaly coefficients. We also present a simple model realizing a multiple axion monodromy along the inflaton direction.
118442232
String theoretic QCD axions in the light of PLANCK and BICEP2
A bstractThe QCD axion solving the strong CP problem may originate from antisymmetric tensor gauge fields in compactified string theory, with a decay constant around the GUT scale. Such possibility appears to be ruled out now by the detection of tensor modes by BICEP2 and the PLANCK constraints on isocurvature density perturbations. A more interesting and still viable possibility is that the string theoretic QCD axion is charged under an anomalous U(1)A gauge symmetry. In such case, the axion decay constant can be much lower than the GUT scale if moduli are stabilized near the point of vanishing Fayet-Illiopoulos term, and U(1)A-charged matter fields get a vacuum value v ~ (mSUSYMPln)1/(n + 1) (n ≥ 0) induced by a tachyonic SUSY breaking mass mSUSY. We examine the symmetry breaking pattern of such models during the inflationary epoch with HI ≃ 1014 GeV, and identify the range of the QCD axion decay constant, as well as the corresponding relic axion abundance, consistent with known cosmological constraints. In addition to the case that the PQ symmetry is restored during inflation, i.e. v(tI) = 0, there are other viable scenarios, including that the PQ symmetry is broken during inflation with v(tI) ∼ (4πHIMPln)1/(n + 1) ~ 1016–1017 GeV due to the Hubble-induced D-term DA ~ 8π2HI2, while v(t0) ~ (mSUSYMPln)1/(n + 1) ~ 109–5 × 1013 GeV in the present universe, where v(t0) above 1012 GeV requires a fine-tuning of the axion misalignment angle. We also discuss the implications of our results for the size of SUSY breaking soft masses.