arXiv subjects
Publications and source records attributed to Sang-Jin Sin.
We study the effect of the Dp-brane gas in string cosmology. When one kind of Dp-brane gas dominates, we find that the cosmology is equivalent to that of the Brans-Dicke theory with the perfect fluid type matter. We obtain $γ$, the equation of state parameter, in terms of p and the space-time dimension.
We study the cosmology of the Brans-Dicke(BD) theory coupled to perfect fluid type matter. In our previous works, the case where matter is coming from the Ramond-Ramond sector of the string theory was studied. Here, we study the case where matter is coming from the NS-NS sector. Exact solutions are found and the cosmology is classified according to the values of $γ$, the parameter of the equation of state and $ω$, Brans-Dicke parameter. We find taht, in string frame, there are solutions without singularity for some ranges of $γ$ and $ω$. In Einstein frame, however, all solutions are singular.
Using the AdS/CFT correspondence and the eikonal approximation, we evaluate the elastic parton-parton scattering amplitude at large $N$ and strong coupling $g^2N$ in N=4 SYM. We obtain a scattering amplitude with a Regge behavior that unitarizes at large $\sqrt{s}$.
We generalize the M-theoretic duality of Schmaltz and Sundrum to the product group SU(N) x SU(N') case. We show that the type IIA brane configurations for dual gauge theories are in fact two special limits of the same M-theory 5-brane, just as in the case of the simple SU(N) group.
We study the cosmology of the Brans-Dicke theory with perfect fluid type matter. In our previous work, we found exact solutions for any Brans-Dicke parameter $ω$ and for general parameter $γ$ of equation of state. In this paper we further study the cosmology of these solutions by analyzing them according to their asymptotic behaviors. The cosmology is classified into 19 phases according to the values of $γ$ and $ω$. The effect of the cosmological constant to the Brans-Dicke theory is a particular case of our model. We give plot of time evolution of the scale factor by numerical investigations. We also give a comparison of the solutions for the theories with and without matter.
We show that the D-instanton in the $AdS_5 \times S^5$ background is a wormhole connecting the background $AdS_5 \times S^5$ to the flat space $\bf R^{10}$ located at the position of the D-instanton. By a $SL(2,{\bf R})$ rotation of type IIB theory, we can make the {\it global} geometry flat in string frame. We also find that, due to the tight relation between the dilaton and the axion, there is no $SL(2,{\bf R})$ element that takes strong string coupling to weak one without making the axion ill defined. We also discuss the case of $AdS_3$ as well as the instanton gases. A subtlety on the D-instanton at the boundary or at the horizon is discussed.
We study the effect of the solitonic degrees of freedom in string cosmology following the line of Rama. The gas of solitonic p-brane is treated as a perfect fluid in a Brans-Dicke type theory. In this paper, we find exact cosmological solutions for any Brans-Dicke parameter $ω$ and for general parameter $γ$ of equation of state and classify the cosmology of the solutions on a parameter space of $γ$ and $ω$.
We study the holomorphic properties of the MQCD by comparing the super-potentials in MQCD and the gauge theory. First we show that the super-potential defined as an integral of three form is NOT appropriate for generic situation with quarks. We report a resolution of the problem which works for the brane configurations of 90 degree rotation, including the true SQCD. The new definition does not need auxiliary surface and can be reduced to a contour integral for some cases. We find relation beetween the new and old definitions, which is verified by explicit calculation for SU(N), SO(N), Sp(N) simple groups with $F$ of massive quarks.
We consider brane configurations in M-theory describing N=1 supersymmetric gauge theories and using the parametric representation of the brane configurations, we calculate the superpotentials for various cases including multiple gauge groups or fermions. For SU(n) N=1 SQCD with $N_f$ fermion case ($N_f < N_c)$, we find that the superpotential from M-theory and the gauge theory agree precisely. This gives a direct evidence of the validity of Witten's M-theory method for calculating the super potential.
We study the effect of the solitonic degree of freedom in string cosmology following the line of Rama. The gas of solitonic p-brane is treated as a perfect fluid in a Brans-Dicke type theory. In this paper, we find analytic solutions for a few solvable cases of equation of states with general Brans-Dicke parameter $ω$ and study the cosmology of the solutions. In some cases the solutions are free from initial singularity.
We present a renormalization-group (RG) flow argument for s-wave kaon condensation in dense nuclear-star matter predicted in chiral perturbation theory. It is shown that it is the {\it relevant} mass term together with {\it any} attractive interaction for the kaon in medium that triggers the instability. We show that a saddle point of multi-dimensional RG flow can imply a phase transition. Pion condensation is also analyzed along the same line of reasoning.
We consider the ultra light pseudo Nambu-Goldstone boson appearing in the late time cosmological phase transition theories as a dark matter candidate. Since it is almost massless, its nature is more wave like than particle like. Hence we apply quantum mechanics to study how they form the galactic halos. Three predictions are made; (1)the mass profile $ρ\sim r^{-1.6}$, (2)there are ripple-like fine structures in rotation curve, (3) the rotation velocity times ripple's wave length is largely galaxy independent. We compare the rotation curves predicted by our theory with the data observed.