We study the holographic light meson spectra and their mass splitting in the nuclear medium.In order to describe the nuclear matter, we take into account the thermal charged AdS geometry with two flavor charges, which can be reinterpreted as the number densities of proton and neutron after some field redefinitions. We show that the meson mass splitting occurs when there exists the density difference between proton and neutron. Depending on the flavor charge, the mass of the positively (negatively) charged meson increases (decreases) as the density difference increases, whereas the neutral meson mass is independent of the density difference. In the regime of the large nucleon density with a relatively large number difference between proton and neutron, we find that negatively charged pion becomes massless in the nuclear medium, so the pion condensate can occur. We also investigate the binding energy of a heavy quarkonium in the nuclear medium, in which the binding energy of a heavy quarkonium becomes weaker as the density difference increases. *

We classify the cosmological behaviors of the domain wall under junctions between two spacetimes in terms of various parameters: cosmological constants of bulk spacetime, a tension of a domain wall, and mass parameters of the black hole-type metric. Especially, we consider the false-true vacuum type junctions and the domain wall connecting between an inner AdS space and an outer AdS Reissner-Nordstr${\rm \ddot{o}}$m black hole. We find that there exist a solution to the junction equations with an inflation at earlier times and an accelerating expansion at later times.Comment: corrected typos, title and sec.

In the framework of a holographic QCD approach we study an influence of matters on the deconfinement temperature, T c . We first consider quark flavor number (N f ) dependence of T c . We observe that T c decreases with N f , which is consistent with a lattice QCD result. We also delve into how the quark number density ρ q affects the value of T c . We find that T c drops with increasing ρ q . In both cases, we confirm that the contributions from quarks are suppressed by 1/N c , as it should be, compared to the ones from a gravitational action (pure Yang-Mills).

By using the gauge/gravity duality, we investigate the dual field theories of the anisotropic backgrounds, which are exact solutions of Einstein-Maxwell-dilaton theory with a Liouville potential. When we turn on the bulk gauge field fluctuation A x with a nontrivial dilaton coupling, the AC conductivity of this dual field theory is proportional to the frequency with an exponent depending on parameters of the anisotropic background. In some parameter regions, we find that this conductivity can have the negative exponent like the strange metal. In addition, we also investigate another Uð1Þ gauge field fluctuation, which is not coupled with a dilaton field. We classify all possible conductivities of this system and find that the exponent of the conductivity is always positive.

We study the dynamics of false vacuum bubbles. A nonminimally coupled scalar field gives rise to the effect of negative tension. The mass of a false vacuum bubble from outside observer's point of view can be positive, zero, or negative. The interior false vacuum has de Sitter geometry, while the exterior true vacuum background can have geometry depending on the vacuum energy. We show that there exist expanding false vacuum bubbles without the initial singularity in the past.Comment: 17 pages, 13 figure