1,233 research outputs found
Graviton Propagators in Supergravity and Noncommutative Gauge Theory
We investigate the graviton propagator in the type IIB supergravity
background which is dual to 4 dimensional noncommutative gauge theory. We
assume that the boundary is located not at the infinity but at the
noncommutative scale where the string frame metric exhibits the maximum. We
argue that the Neumann boundary condition is the appropriate boundary condition
to be adopted at the boundary. We find that the graviton propagator behaves
just as that of the 4 dimensional massless graviton. On the other hand, the
non-analytic behaviors of the other Kaluza-Klein modes are not significantly
affected by the Neumann boundary condition.Comment: 19 page
N=4 Supersymmetric Yang-Mills on S^3 in Plane Wave Matrix Model at Finite Temperature
We investigate the large N reduced model of gauge theory on a curved
spacetime through the plane wave matrix model. We formally derive the action of
the N=4 supersymmetric Yang-Mills theory on R \times S^3 from the plane wave
matrix model in the large N limit. Furthermore, we evaluate the effective
action of the plane wave matrix model up to the two-loop level at finite
temperature. We find that the effective action is consistent with the free
energy of the N=4 supersymmetric Yang-Mills theory on S^3 at high temperature
limit where the planar contributions dominate. We conclude that the plane wave
matrix model can be used as a large N reduced model to investigate
nonperturbative aspects of the N=4 supersymmetric Yang-Mills theory on R \times
S^3.Comment: 31pages: added comments and reference
A closer look at string resonances in dijet events at the LHC
The first string excited state can be observed as a resonance in dijet
invariant mass distributions at the LHC, if the scenario of low-scale string
with large extra dimensions is realized. A distinguished property of the dijet
resonance by string excited states from that the other "new physics" is that
many almost degenerate states with various spin compose a single resonance
structure. It is examined that how we can obtain evidences of low-scale string
models through the analysis of angular distributions of dijet events at the
LHC. Some string resonance states of color singlet can obtain large mass shifts
through the open string one-loop effect, or through the mixing with closed
string states, and the shape of resonance structure can be distorted. Although
the distortion is not very large (10% for the mass squared), it might be able
to observe the effect at the LHC, if gluon jets and quark jets could be
distinguished in a certain level of efficiency.Comment: 12 pages, 8 figure
symmetry of the BKT transition and twisted boundary conditio n
Berezinskii-Kosterlitz-Thouless (BKT) transition, the transition of the 2D
sine-Gordon model, plays an important role in the low dimensional physics. We
relate the operator content of the BKT transition to that of the SU(2)
Wess-Zumino-Witten model, using twisted boundary conditions. With this method,
in order to determine the BKT critical point, we can use the level crossing of
the lower excitations than the periodic boundary case, thus the convergence to
the transition point is highly improved. Then we verify the efficiency of this
method by applying to the S=1,2 spin chains.Comment: LaTex2e,, 33 pages, 14 figures in eps file
Pseudogap of Color Superconductivity in Heated Quark Matter
We show that the pseudogap of the quark density of states is formed in hot
quark matter as a precursory phenomenon of the color superconductivity on the
basis of a low-energy effective theory. We clarify that the decaying process of
quarks near Fermi surface to a hole and the diquark soft mode (qq)_{soft} is
responsible for the formation of the pseudogap. Our result suggests that the
pseudogap is a universal phenomenon in strong coupling superconductors.Comment: Introduction is largely rewritten and minor changes are made in other
parts of the text. Some referenes with comments are added. Numerical errors
in the figures are corrected. To appear in Phys. Rev.
Phase diagram of S=1 XXZ chain with next-nearest neighbor interaction
The one dimensional S=1 XXZ model with next-nearest-neighbor interaction
and Ising-type anisotropy is studied by using a numerical
diagonalization technique. We discuss the ground state phase diagram of this
model numerically by the twisted-boundary-condition level spectroscopy method
and the phenomenological renormalization group method, and analytically by the
spin wave theory. We determine the phase boundaries among the XY phase, the
Haldane phase, the ferromagnetic phase and the N\'{e}el phase, and then we
confirm the universality class. Moreover, we map this model onto the non-linear
model and analyze the phase diagram in the -1 and
1 region by using the renormalization group method.Comment: 18 pages, 10 figure
Infra-red effects of Non-linear sigma model in de Sitter space
We extend our investigation on a possible de Sitter symmetry breaking
mechanism in non-linear sigma models. The scale invariance of the quantum
fluctuations could make the cosmological constant time dependent signaling the
de Sitter symmetry breaking. To understand such a symmetry breaking mechanism,
we investigate the energy-momentum tensor. We show that the leading infra-red
logarithms cancel to all orders in perturbation theory in a generic non-linear
sigma model. When the target space is an N sphere, the de Sitter symmetry is
preserved in the large N limit. For a less symmetric target space, the
infra-red logarithms appear at the three loop level. However there is a counter
term to precisely cancel it. The leading infra-red logarithms do not cancel for
higher derivative interactions. We investigate such a model in which the
infra-red logarithms first appear at the three loop level. A nonperturbative
investigation in the large N limit shows that they eventually grow as large as
the one loop effect.Comment: 39page
Phase Diagrams of S=3/2, 2 XXZ Spin Chains with Bond-Alternation
We study the phase diagram of S=3/2 and S=2 bond-alternating spin chains
numerically. In previous papers, the phase diagram of S=1 XXZ spin chain with
bond-alternation was shown to reflect the hidden symmetry.
But for the higher S Heisenberg spin chain, the successive dimerization
transition occurs, and for anisotropic spin chains the phase structure will be
more colorful than the S=1 case. Using recently developed methods, we show
directly that the phase structure of the anisotropic spin chains relates to the
symmetry.Comment: 13 pages, 6 figures(eps), RevTe
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