Family Gauge Boson Production at the LHC

Family gauge boson production at the LHC is investigated according to a $U(3)$ family gauge model with twisted family number assignment. In the model we study, a family gauge boson with the lowest mass, $A_1^{\ 1}$, interacts only with the first generation leptons and the third generation quarks. (The family numbers are assigned, for example, as $(e_1, e_2, e_3)= (e^-, \mu^-, \tau^-)$ and $(d_1, d_2, d_3)=(b, d, s)$[or $(d_1, d_2, d_3)=(b, s, d)$]). In the model, the family gauge coupling constant is fixed by relating to the electroweak gauge coupling constant. Thus measurements of production cross sections and branching ratios of $A_1^{\ 1}$ clearly confirm or rule out the model. We calculate the cross sections of inclusive $A_1^{\ 1}$ production and $b \bar{b} \, (t \bar{t})$ associated $A_1^{\ 1}$ production at $\sqrt{s} = 14~\text{TeV}$ and $100~\text{TeV}$. With the dielectron production cross section, we discuss the determination of diagonalizing matrix of quark mass matrix, $U_{u}$ and $U_{d}$, respectively.Comment: 14 pages, 6 figure

Kadanoff-Baym approach to the thermal resonant leptogenesis

Using the non-equilibrium Green function method (Kadanoff-Baym equations) in the expanding universe, we investigate evolution of the lepton number asymmetry when the right-handed (RH) neutrinos have almost degenerate masses $|M_i^2-M_j^2| \ll M_i^2$. The resonantly enhanced $CP$-violating parameter $\varepsilon_i$ associated with the decay of the RH neutrino $N_i$ is obtained. It is proportional to an enhancement factor $(M_i^2-M_j^2) M_i \Gamma_j/ ((M_i^2-M_j^2)^2 +R_{ij}^2)$ with the regulator $R_{ij}=M_i \Gamma_i+M_j \Gamma_j$. The result is consistent with the previous result obtained by Garny et al., in a constant background with an out-of-equilibrium initial state. We discuss the origin of such a regulator, and why it is not like $R_{ij}=M_i \Gamma_i-M_j \Gamma_j$.Comment: 51 pages + appendices (46 pages), 5 figures; typos corrected, references adde

Solving cosmological problem in universal extra dimension models by introducing Dirac neutrino

Universal extra dimension (UED) models with right-handed neutrinos are studied. The introduction of the neutrinos makes us possible not only to describe Dirac neutrino masses but also to solve the cosmological problem called the KK graviton problem. This problem is essentially caused by the late time decay of a KK photon into a KK graviton and a photon, and it distorts the spectrum of the cosmic microwave background or the diffuse photon. We point out that, once we introduce right-handed neutrinos to UED models, the KK photon decays dominantly into neutrinos and does not emit a photon. We also discuss sub-dominant modes with a photon in the decay quantitatively, and show that their branching ratios are so small that the spectra are not distorted.Comment: Some discussions are added

Flavor violating Z′Z' from SO(10)SO(10) SUSY GUT in High-Scale SUSY

We propose an $SO(10)$ supersymmetric grand unified theory (SUSY GUT), where the $SO(10)$ gauge symmetry breaks down to $SU(3)_c \times SU(2)_L \times U(1)_Y\times U(1)_{X}$ at the GUT scale and $U(1)_X$ is radiatively broken at the SUSY-braking scale. In order to achieve the observed Higgs mass around $126$ GeV and also to satisfy constraints on flavor- and/or CP-violating processes, we assume that the SUSY-breaking scale is $O(100)$ TeV, so that the $U(1)_X$ breaking scale is also $O(100)$ TeV. One big issue in the SO(10) GUTs is how to realize realistic Yukawa couplings. In our model, not only ${\bf 16}$-dimensional but also ${\bf 10}$-dimensional matter fields are introduced to predict the observed fermion masses and mixings. The Standard-Model quarks and leptons are linear combinations of the ${\bf 16}$- and ${\bf 10}$-dimensional fields so that the $U(1)_{X}$ gauge interaction may be flavor-violating. We investigate the current constraints on the flavor-violating $Z'$ interaction from the flavor physics and discuss prospects for future experiments.Comment: 13 pages, IPMU-15-003

Direct Detection of Vector Dark Matter

In this paper we complete formulae for the elastic cross section of general vector dark matter with nucleon in the direct detection at the leading order of the strong coupling constant, assuming that the dark matter is composed of vector particles. As an application of our formulae, the direct detection of the first Kaluza-Klein photon in the minimal universal extra dimension model is discussed. It is found that the cross section is larger than those in the previous works by up to a factor of ten.Comment: 22 pages, 11 figures; two typos in equations are correcte