15628636
Multiple scalar particle decays and perturbation generation
We study the evolution of the universe which contains multiple non-relativistic scalar fields decaying into both radiation and pressureless matter. We present a powerful analytic formalism for calculating the matter and radiation curvature perturbations, and find that our analytic estimates agree with full numerical results within an error of less than one per cent. Also we discuss the isocurvature perturbation of matter and radiation components, which may be detected by near future cosmological observations, and point out that it crucially depends on the branching ratio of the decay rate of the scalar fields and that it is hard to make any model independent predictions.
118604242
Quasar polarization with two axionlike particles
Abstract Recently, it was shown, that the absence of circular polarization of visible light from quasars, severely constrains the interpretation of axion like particles (ALPs) as a solution for the generation of the linear polarization. Furthermore, the new observation of the linear polarization in the radio wavelength from quasars, similar to the earlier observation performed in the optical band, makes the ALPs scenario inconsistent with at least one of the two observations. In this study we extend this scenario, to two axion like particles, one scalar and another pseudoscalar. We find, that the effects from scalar and pseudoscalar cancel out each other, thereby suppressing the circular polarization, while preserving consistent linear polarization, as observed in both visible and radio waves bands.
119366917
Double suppression of FCNCs in supersymmetric models
A mechanism for double suppression of flavor-changing neutral currents (FCNCs) and CP violating phases in supersymmetric models is suggested. At M{sub SUSY} they are suppressed due to a nonabelian discrete flavor symmetry, and the infrared attractive force of gauge interactions in extra dimensions are used to suppress them at the compactification scale. We present a concrete model, which is a simple extension of S{sub 3} invariant minimal supersymmetric standard model, where only SU(2){sub L} and SU(3){sub C} gauge multiplets are assumed to propagate in the bulk. We find that a disorder of 2 orders of magnitude in soft supersymmetry breaking parameters above the compactification scale may be allowed to satisfy experimental constraints on FCNC processes and CP violating phenomena.
14862395
Softness of brane-localized supersymmetry breaking on orbifolds
Abstract We consider the brane-localized supersymmetry breaking in 5D compactified on S 1 / Z 2 . In case of a bulk gaugino with arbitrary brane masses for its even and odd modes, we find the mass spectrum and the wave functions of gaugino. We show that the gaugino masses at the distant brane are soft in the usual sense in the effective field theory with zero modes of bulk gauge fields and they are also extremely soft in view of the one-loop finite mass of a brane scalar in the KK regularization.
42769057
Conditions for large non-Gaussianity in two-field slow-roll inflation
We study the level of primordial non-Gaussianity in slow-roll two-field inflation. Using an analytic formula for the non-linear parameter fNL in the case of a sum or product separable potential, we find that it is possible to generate significant non-Gaussianity even during slow-roll inflation with Gaussian perturbations at Hubble exit. In this paper we give the general conditions for obtaining large non-Gaussianity and calculate the level of fine-tuning required to obtain this. We present explicit models in which the non-Gaussianity at the end of inflation can exceed the current observational bound of .
7390821
Spectral running and non-Gaussianity from slow-roll inflation in generalized two-field models
Theories beyond the standard model such as string theory motivate low energy effective field theories with several scalar fields which are not only coupled through a potential but also through their kinetic terms. For such theories we derive the general formulae for the running of the spectral indices for the adiabatic, isocurvature and correlation spectra in the case of two-field inflation. We also compute the expected non-Gaussianity in such models for specific forms of the potentials. We find that the coupling has little impact on the level of non-Gaussianity during inflation.
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.
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.
120235525
Some New Features in the Pseudoscalar Meson and Vector Meson Photoproductions
We investigate the role of the t-channel meson exchange in various photoproduction processes to discuss features of the respective production mechanism. For the less model-dependent analysis we work with the t-channel meson pole reggeized in the Born approximation amplitude. With the meson–baryon coupling constants chosen consistently with symmetry prediction we show that the Reggeized pole model could reproduce the experimental data to a good degree in the lower energy region. Numerical consequences show the significance of the tensor meson exchange in the γp → K+Λ, the dominance of the pseudoscalar meson exchange in the πΔ (and KΣ*) processes, and the sizable role of the vector-meson magnetic moment in the charged ρ (and K*) photoproductions, respectively. These new features from the present analyses could provide a useful guide for future study of the N* resonances in the low energy region.
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.
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.