1,680 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
BCS-BEC crossover in a relativistic superfluid and its significance to quark matter
The character change of a superfluid state due to the variation of the
attractive force is investigated in the relativistic framework with a massive
fermion. Two crossovers are found. One is a crossover from the usual BCS state
to the Bose-Einstein condensation (BEC) of bound fermion pairs. The other is
from the BEC to the relativistic Bose-Einstein condensation (RBEC) of nearly
massless bound pairs where antiparticles as well as particles dominate the
thermodynamics. Possible realization of the BEC and RBEC states in the quark
matter is also pointed out.Comment: 5 pages, 1 figure, revtex4; (v2) text has been clarified, references
updated; (v3) final version to appear in Phys. Rev.
Setting Children Free: Children’s Independent Movement in the Local Environment
Parental concerns about children’s safety and security are restricting children’s independent exploration of the local environment. Children are being denied important opportunities to exercise, to acquire decision-making skills, such as crossing the road safely, and to develop social skills through interaction with their peers. This paper presents findings from the project CAPABLE (Children’s Activities, Perceptions And Behaviour in the Local Environment) being carried out at University College London. Based on findings from fieldwork carried out with children aged 8-11 in Cheshunt, Hertfordshire, the paper shows the effect of factors such as the number of adults at home, having an older sibling, having a car or garden at home and living near to a park on the propensity to be allowed out alone. Then it considers how being allowed out alone affects the amount of time children spend outdoors, playing with friends and watching television. The paper then uses data from children who have been fitted with physical activity monitors and GPS (Global Positioning Satellite) monitors and asked to keep diaries, to show how children’s travel behaviour differs when they are with adults from when they are not
Finite-Field Ground State of the S=1 Antiferromagnetic-Ferromagnetic Bond-Alternating Chain
We investigate the finite-field ground state of the S=1
antiferromagnetic-ferromagnetic bond-alternating chain described by the
Hamiltonian
{\calH}=\sum\nolimits_{\ell}\bigl\{\vecS_{2\ell-1}\cdot\vecS_{2\ell}
+J\vecS_{2\ell}\cdot\vecS_{2\ell+1}\bigr\} +D\sum\nolimits_{\ell}
\bigl(S_{\ell}^z)^2 -H\textstyle\sum\nolimits_\ell S_\ell^z, where
\hbox{} and \hbox{}. We find that two kinds of
magnetization plateaux at a half of the saturation magnetization, the
1/2-plateaux, appear in the ground-state magnetization curve; one of them is of
the Haldane type and the other is of the large--type. We determine the
1/2-plateau phase diagram on the versus plane, applying the
twisted-boundary-condition level spectroscopy methods developed by Kitazawa and
Nomura. We also calculate the ground-state magnetization curves and the
magnetization phase diagrams by means of the density-matrix
renormalization-group method
Ground State Phase Diagram of S=1 XXZ Chains with Uniaxial Single-Ion-Type Anisotropy
One dimensional S=1 XXZ chains with uniaxial single-ion-type anisotropy are
studied by numerical exact diagonalization of finite size systems. The
numerical data are analyzed using conformal field theory, the level
spectroscopy, phenomenological renormalization group and finite size scaling
method. We thus present the first quantitatively reliable ground state phase
diagram of this model. The ground states of this model contain the Haldane
phase, large-D phase, N\'{e}el phase, two XY phases and the ferromagnetic
phase. There are four different types of transitions between these phases: the
Brezinskii-Kosterlitz-Thouless type transitions, the Gaussian type transitions,
the Ising type transitions and the first order transitions. The location of
these critical lines are accurately determined.Comment: 8 pages, 19 figure
Fermionic zero-modes in type II fivebrane backgrounds
The explicit form of the fermionic zero-modes in the fivebrane backgrounds of
type IIA and IIB supergravity theories is investigated. In type IIA fivebrane
background there are four zero-modes of gravitinos and dilatinos. In type IIB
fivebrane background four zero-modes of dilatinos and no zero-modes of
gravitinos are found. These zero-modes indicate the four-fermion condensates
which have been suggested in a calculation of the tension of the D-brane in
fivebrane backgrounds.Comment: 10 page
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
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
Field-induced magnetic ordering in the Haldane system PbNi2V2O8
The Haldane system PbNi2V2O8 was investigated by the temperature dependent
magnetization M(T) measurements at fields higher than H_c, with H_c the
critical fields necessary to close the Haldane gap. It is revealed that M(T)
for H > H_c exhibits a cusp-like minimum at T_{min}, below which M(T) increases
with decreasing T having a convex curve. These features have been observed for
both and , with c-axis being parallel to the chain.
These data indicate the occurrence of field-induced magnetic ordering around
T_{min}. Phase boundaries for and do not cross each
other, consistent with the theoretical calculation for negative single-ion
anisotropy D.Comment: 3 figures, submitted to 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
- …