Poster Presentations

Abstract:
We discuss modified gravitational theories to explain the current accelerated expansion of the universe, so-called dark energy problem, whose observational and theoretical backgrounds are also introduced. In particular, we investigate finite-time future singularities in non-local gravity as well as $f(T)$ gravity with $T$ being the torsion scalar. It is found that three types of the finite-time future singularities can occur in non-local gravity [1]. Furthermore, it is explicitly demonstrated that there appear finite-time future singularities in $f(T)$ gravity and an $f(T)$ gravity model with realizing those singularities is reconstructed [2]. We also study $f(T)$ gravity models to various cosmological scenarios related to finite-time future singularities [2]. Main references: [1] K. Bamba, S. Nojiri, S. D. Odintsov and M. Sasaki, Gen. Relativ. Gravit. 44, 1321 (2012) [arXiv:1104.2692 [hep-th]]. [2] K. Bamba, R. Myrzakulov, S. Nojiri and S. D. Odintsov, Phys. Rev. D 85, 104036 (2012) [arXiv:1202.4057 [gr-qc]].

Abstract:
We have revisited the calculation of the neutron electric dipole moment in the presence of the CP-violating operators up to dimension five based on the chiral perturbation theory. Especially, we focus on the contribution of strangeness content. In the calculation, we extract the nucleon matrix elements of scalar-type quark operators from the results of the lattice QCD simulations, while those of the dipole-type quark-gluon operators are evaluated by using the method of the QCD sum rules. As a result, it is found that although the strangeness quantity in nucleon is small, the contribution of the chromoelectric dipole moment of strange quark may be still sizable, and thus may offer a sensitive probe for the CP-violating interactions in physics beyond the Standard Model.

Abstract:
The ATLAS and CMS experiments have recently discovered a new 125 GeV scalar boson. We show that the properties of this scalar, including the enhancement of its diphoton decay rate, can be naturally explained in a model with an isospin symmetric Higgs boson. The predictions of the model relevant for future experiments are also discussed.

Abstract:
Inspired by the small squared-mass difference measured in solar neutrino oscillation experiments and observability in neutrinoless double beta decay experiments, we suggest that the partial mass-degenerate limit, in which masses of the first two generation fermions are degenerate, may be a good starting point for understanding the observed fermion mass spectra and mixing patterns. The limit indicates an $O(2)$ symmetry acting on flavor space of the first two generations. We propose a simple model for the lepton sector based on the $D_N$ group, which is a discrete subgroup of $O(2)$, and show that the model can successfully reproduce the experimental data without tuning dimension couplings.

Abstract:
We calculate techni-pion masses in the Farhi-Susskind one-family technicolor model, explicitly by evaluating nontrivial contributions from walking dynamics along with various possible chiral breaking sources. Our computation reveals that the techni-pions cannot be either much lighter or heavier than other techni-hadrons, due to the essential walking features: the masses still remain at scales as high as several hundred GeV. The phenomenological implications to the ongoing LHC are discussed focusing on neutral isosinglet techni-pions.

Abstract:
The dual superconductivity is the promising mechanism for quark confinement. We have proposed the non-Abelian dual superconductivity picture in the SU(3) Yang-Mills theory, and already presented numerical evidences for the restricted U(2)-field dominance and the non-Abelian magnetic monopole dominance in the string tension, by applying our new formulation of Yang-Mills theory to a lattice. In this talk, we focus on the non-Abelian dual Meissner effect and the type of dual superconductivity. We find that the measured chromo-electric flux tube between a quark and antiquark pair strongly supports the non-Abelian dual Meissner effect due to non-Abelian magnetic monopoles. Moreover, we give a remarkable result that the type of the resulting dual superconductor is the type I in SU(3) Yang-Mills, rather than the border between the type I and II, in marked contrast to the SU(2) case.

Abstract:
Our target to analyze the dynamical chiral symmetry breaking is the mass function, which is the first derivative of the Wilsonian effective potential for the bilinear fermion operators. It satisfies the nonperturbative renormalization group equation (NPRGE), a partial differential equation (PDE) of the conservation law type. We solve the NPRGE of the mass function, which is a regular function at the initial scale. In case that the dynamical chiral symmetry breaking occurs, the mass function must have some singular behavior. Therefore, the mass function evolves such singularity on the way to the infrared scale. Such evolution is unacceptable as a solution of the PDE, but it is known that we may treat such solution as the "weak solution" of the PDE. Taking the Nambu-Jona-Lassinio model, we construct the weak solution by using the method of characteristics. We prove the uniqueness of the weak solution and it correctly describes the dynamical symmetry breaking. We calculate chiral order parameters at the infrared successfully only with fermionic operators.

Abstract:
Anomalous $U(1)_A$ SUSY GUT models are attractive because they can solve many difficulties in SUSY GUT models. One of the most important predictions of anomalous $U(1)_A$ SUSY GUT is that nucleon decay amplitudes via dim 6 effective int. are enhanced and rough estimation gives $\tau(p\rightarrow \pi^0+e^+)\sim 10^{34}$ years which is nothing but the present experimental lower bound, while nucleon decay amplitudes via dim 5 effective int. are suppressed. Then we calculate dim 6 effective int. and nucleon lifetimes for each decay mode in $SU(5),SO(10)$ or $E_6$ GUT models with various unitary matrices which diagonalize Yukawa matrices. In this calculation we use more than 50000 model points.

Abstract:
We study the neutron electric dipole moment in the presence of the CP-violating operators up to the dimension five in terms of the QCD sum rules. It is found that the OPE calculation is robust when exploiting a particular interpolating field for neutron, while there exist some uncertainties on the phenomenological side. By using input parameters obtained from the lattice calculation, we derive a conservative limit for the contributions of the CP violating operators.

Abstract:
Recently, 3-dimensional SUSY gauge theory have made progress. Localization techniques enable us to calculate the partition function and the supersymmetric Wilson loop exactly. These results are expressed as matrix integrals. We further calcularte these quantity. In this poster, we want to explain recent progress. 3-dim. SUSY gauge theory is very fun. I want to convey the fun.

Abstract:
Owing to its outstanding feature, dynamical chiral symmetry breaking phenomena have been widely studied in many fields. In the gauge theory, the spontaneous symmetry breaking generates masses for fermions. The standard method to discuss the spontaneous mass generation is to formulate a coupled system of self-consistent equations. However, those equations are no more than the necessary condition and it is needed to reconsider solutions to obtain correct one by using another means. One way is to evaluate the free energy of each solution. Even if it is performed, there are still unclear points whether the minimal free energy ensures the meaningful correct answer. We adopt the Nambu-Jona-Lasinio model and give a new iteration method that directly sums up an infinite number of diagrams in the ladder approximation. Using this method, we demonstrate that the physically meaningful solution is automatically reached and the critical coupling constant is found. Furthermore, we extend the method to the system at finite density. We report that there are cases where the method does not work well as it is on account of different structures of phase transitions. We also disucuss the relation between the iteration method and the renormalization group equation method with weak solution.

Abstract:
We present a measurement of the Schrödinger Functional running coupling in SU(2) lattice gauge theory with adjoint fermions. We use HEX smearing and clover improvement to reduce the discretization effects. The results suggest the existence of a non-trivial infrared fixed point.

Abstract:
The method of non-perturbative renormalization group (NPRG) is applied to the dynamical chiral symmetry breaking in QCD. The NPRG equation is given as a partial differential equation of the effective action defined with the infrared cutoff. Lowering the cutoff scale, this differential equation interpolates between the bare action and the full corrected effective action. The chiral symmetry breaking is realized as the divergence of the 4-fermi coupling constant at an infrared cutoff scale in the fermion operator space of the effective action without introducing the meson fields. Within the field operator expansion, it is difficult to access the cut off scale lower than its critical scale. However, if we regard the solution including the singular point as the so-called weak solution of the partial differential equation, the solution lower than the critical scale can be obtained. We discuss the uniqueness of the weak solution, and apply it to beyond the ladder analysis in QCD.

Abstract:
The renormalization-group equations for the (flavor-conserving) CP-violating interaction are derived up to the dimension six, including all the four-quark operators, at one-loop level. We apply them to the models with extended scalar sector which have CP-violating Yukawa interactions with quarks, and discuss the electric dipole moment in these models.

Abstract:
We study the possibility that the scalar mesons exist as four-quark states. The energy shift of two pseudoscalar mesons as a function of spatial lattice size makes a distinction between bound states and scattering states of four-quark states. We calculate the four-quark state in the quenched approximation, ignoring the two-quark annihilation diagrams and the vacuum channels. We perform a calculation of pseudoscalar meson scattering amplitudes, using Nf = 2 Wilson fermion and plaquette/Iwasaki gauge actions. We obtain the indication that the four-quark states in the case of the isospin zero (I = 0) and two (I = 2) channels are no bound states. And we find that the bound energy depends strongly on pion mass rather than the ratio of pion mass to rho meson mass.

Abstract:
It is well known that the SU(3) gauge theory with the fundamental 16-flavor fermion is governed by a non-trivial infrared fixed point in the 2-loop perturbation theory, while the theory has not been well investigated by non-perturbative lattice simulations. We investigate properties of 16-flavor QCD by lattice simulation with highly improved actions(HISQ/tree) at sevral lattice spacings. We present the results for the mass of the lightest pseudoscalar meson, and its decay constant at non-zero fermion mass. We discuss the finite-mass and finite-volume scaling of the quantities, the mass anomalous dimension extracted from the scaling, and comparison of the anomalous dimension with the perturbation theory.

Abstract:
A free single-particle state is defined as unitary irreducible representation of Poincaré group. E. Wigner has investigated that these representations classified by mass, momentum and representation of little group. In particular, for massless particle the little group is ISO(2), namely two dimensional Euclidean group which contains one rotation and two translations. Eigenvalues of the rotation is called helicity. On the other hand, it has shown that translations generate abelian gauge transformation by S. Weinberg et al. We investigate that this result can be generalized to the case of non-abelian gauge transformation.