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K. Tsumura

Publications and source records attributed to K. Tsumura.

25 records · Page 2Linked to original sources
arXiv2008

Survival of charmonia above Tc in anisotropic lattice QCD

We find a strong evidence for the survival of $J/Ψ$ and $η_c$ as spatially-localized $c\bar c$ (quasi-)bound states above the QCD critical temperature $T_c$, by investigating the boundary-condition dependence of their energies and spectral functions. In a finite-volume box, there arises a boundary-condition dependence for spatially spread states, while no such dependence appears for spatially compact states. In lattice QCD, we find almost {\it no} spatial boundary-condition dependence for the energy of the $c\bar c$ system in $J/Ψ$ and $η_c$ channels for $T\simeq(1.11-2.07)T_c$. We also investigate the spectral function of charmonia above $T_c$ in lattice QCD using the maximum entropy method (MEM) in terms of the boundary-condition dependence. There is {\it no} spatial boundary-condition dependence for the low-lying peaks corresponding to $J/Ψ$ and $η_c$ around 3GeV at $1.62T_c$. These facts indicate the survival of $J/Ψ$ and $η_c$ as compact $c\bar c$ (quasi-)bound states for $T_c < T < 2T_c$.

hep-lat↗
arXiv2006

Derivation of Covariant Dissipative Fluid Dynamics in the Renormalization-group Method

We derive generic relativistic hydrodynamical equations with dissipative effects from the underlying Boltzmann equation in a mechanical and systematic way on the basis of so called the renormalization-group (RG) method. A macroscopic frame vector is introduced to specify the frame on which the macroscopic dynamics is described. Our method is so mechanical with only few ansatz that our method give a microscopic foundation of the available hydrodynamical equations, and also can be applied to make a reduction of the kinetic equations other than the simple Boltzmann equation.

hep-ph↗
arXiv2006

Charmonium properties in deconfinement phase in anisotropic lattice QCD

J/Psi and eta_c above the QCD critical temperature T_c are studied in anisotropic quenched lattice QCD, considering whether the c\bar c systems above T_c are spatially compact (quasi-)bound states or scattering states. We adopt the standard Wilson gauge action and O(a)-improved Wilson quark action with renormalized anisotropy a_s/a_t =4.0 at β=6.10 on 16^3\times (14-26) lattices, which correspond to the spatial lattice volume V\equiv L^3\simeq(1.55{\rm fm})^3 and temperatures T\simeq(1.11-2.07)T_c. We investigate the c\bar c system above T_c from the temporal correlators with spatially-extended operators, where the overlap with the ground state is enhanced. To clarify whether compact charmonia survive in the deconfinement phase, we investigate spatial boundary-condition dependence of the energy of c\bar c systems above T_c. In fact, for low-lying S-wave c \bar c scattering states, it is expected that there appears a significant energy difference ΔE \equiv E{\rm (APBC)}-E{\rm (PBC)}\simeq2\sqrt{m_c^2+3π^2/L^2}-2m_c (m_c: charm quark mass) between periodic and anti-periodic boundary conditions on the finite-volume lattice. In contrast, for compact charmonia, there is no significant energy difference between periodic and anti-periodic boundary conditions. As a lattice QCD result, almost no spatial boundary-condition dependence is observed for the energy of the c\bar c system in J/Ψand η_c channels for T\simeq(1.11-2.07)T_c. This fact indicates that J/Ψand η_c would survive as spatially compact c\bar c (quasi-)bound states below 2T_c. We also investigate a $P$-wave channel at high temperature with maximally entropy method (MEM) and find no low-lying peak structure corresponding to χ_{c1} at 1.62T_c.

hep-lat↗
arXiv2006

Anisotropic lattice QCD studies of penta-quarks and tetra-quarks

Anisotropic lattice QCD studies of penta-quarks(5Q) with J^P=1/2^\pm and 3/2^{\pm} are presented at the quenched level together with tetra-quarks(4Q). The standard gauge action at β=5.75 and O(a) improved quark (clover) action with κ=0.1410(0.010)0.1440 are employed on the anisotropic lattice with the renormalized anisotropy a_s/a_t = 4. The ``hybrid boundary condition(HBC)'' is adopted to discriminate a compact resonance state from scattering states. Only massive 5Q states are found for J^P=1/2^+ and 3/2^{\pm}, which cannot be identified as Θ^+(1540). A low-lying 5Q state is found for J^P=1/2^- at m_{5Q}\simeq 1.75 GeV, which however turns out to be an NK scattering state through the HBC analysis. A preliminary result for 4Q states is presented suggesting an existence of a compact 4Q resonance at m_{4Q} \simeq 1.1 GeV in the idealized SU(4)_f chiral limit.

hep-lat↗
arXiv2004

Yukawa Matrix for the Neutrino and Lepton Flavour Violation

We estimate the magnitude of Lepton Flavour Violation (LFV) from the phase of the neutrino Yukawa matrix. In the minimal supersymmetric standard model with right-handed neutrinos, the LFV processes l_i \to l_j γcan appear through the slepton mixing, which comes from the renormalization group effect on the right-handed neutrino Yukawa interaction between the Grand Unified Theory scale and the heavy right-handed neutrino mass scale. Two types of phases exist in the neutrino Yukawa matrix. One is the Majorana phase, which can change the magnitude of the LFV branching ratios by a few factor. The other phases relate for the size of the Yukawa hierarchy and its phase effect can change the LFV branching ratios by several orders of magnitude.

hep-ph↗
arXiv2004

Phase contribution to LFV

We analyze the phase effect of the neutrino Yukawa matrix in the context of the Minimal Supersymmetric Standard Model with right-handed neutrinos. Its effect can change the Lepton Flavor Violation branching ratios by a few order of magnitude.

hep-ph↗