737 research outputs found
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
First study of semileptonic decay form factors using NRQCD
We present a quenched calculation of the form factors of the semileptonic
weak decay with NRQCD heavy quark and Wilson
light quark on a lattice at . The form factors are
evaluated at six heavy quark masses, in the range of GeV.
dependence of matrix elements are investigated and compared with HQET
predictions. We observe clear signal for the form factors near ,
even at the -quark mass range. is compared with
based on the soft pion theorem and significant difference is
observed.Comment: 3 pages, 5 ps figures, uses espcrc2.sty and epsf.sty, Talk presented
at Lattice'9
R-mediation of Dynamical Supersymmetry Breaking
We propose a simple scenario of the dynamical supersymmetry breaking in four
dimensional supergravity theories. The supersymmetry breaking sector is assumed
to be completely separated as a sequestered sector from the visible sector,
except for the communication by the gravity and U(1)_R gauge interactions, and
the supersymmetry breaking is mediated by the superconformal anomaly and U(1)_R
gauge interaction. Supersymmetry is dynamically broken by the interplay between
the non-perturbative effect of the gauge interaction and Fayet-Iliopoulos
D-term of U(1)_R which necessarily exists in supergravity theories with gauged
U(1)_R symmetry. We construct an explicit model which gives phenomenologically
acceptable mass spectrum of superpartners with vanishing (or very small)
cosmological constant.Comment: 12 pages, to be published in Phys. Rev.
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
Magnetic Properties of J-J-J' Quantum Heisenberg Chains with Spin S=1/2, 1, 3/2 and 2 in a Magnetic Field
By means of the density matrix renormalization group (DMRG) method, the
magnetic properties of the J-J-J quantum Heisenberg chains with spin
, 1, 3/2 and 2 in the ground states are investigated in the presence of
a magnetic field. Two different cases are considered: (a) when is
antiferromagnetic and is ferromagnetic (i.e. the AF-AF-F chain),
the system is a ferrimagnet. The plateaus of the magnetization are observed. It
is found that the width of the plateaus decreases with increasing the
ferromagnetic coupling, and disappears when passes over a
critical value. The saturated field is observed to be independent of the
ferromagnetic coupling; (b) when is ferromagnetic and is
antiferromagnetic (i.e. the F-F-AF chain), the system becomes an
antiferromagnet. The plateaus of the magnetization are also seen. The width of
the plateaus decreases with decreasing the antiferromagnetic coupling, and
disappears when passes over a critical value. Though the ground
state properties are quite different, the magnetization plateaus in both cases
tend to disappear when the ferromagnetic coupling becomes more dominant.
Besides, no fundamental difference between the systems with spin half-integer
and integer has been found.Comment: 8 pages, 9 figures, to be published in J. Phys.: Condens. Matte
Fermion Propagators in Type II Fivebrane Backgrounds
The fermion propagators in the fivebrane background of type II superstring
theories are calculated. The propagator can be obtained by explicitly
evaluating the transition amplitude between two specific NS-R boundary states
by the propagator operator in the non-trivial world-sheet conformal field
theory for the fivebrane background. The propagator in the field theory limit
can be obtained by using point boundary states. We can explicitly investigate
the lowest lying fermion states propagating in the non-trivial ten-dimensional
space-time of the fivebrane background: M^6 x W_k^(4), where W_k^(4) is the
group manifold of SU(2)_k x U(1). The half of the original supersymmetry is
spontaneously broken, and the space-time Lorentz symmetry SO(9,1) reduces to
SO(5,1) in SO(5,1) x SO(4) \subset SO(9,1) by the fivebrane background. We find
that there are no propagations of SO(4) (local Lorentz) spinor fields, which is
consistent with the arguments on the fermion zero-modes in the fivebrane
background of low-energy type II supergravity theories.Comment: 15 page
Bifurcation at the c=3/2 Takhtajan-Babujian point to the c=1 critical lines
We study the S=1 quantum spin chains with bilinear, biquadratic, plus bond
alternation in the vicinity of the S=1 Takhtajan-Babujian model. Transition
line between the Haldane and the dimer phases are determined numerically. To
see the crossover behavior from c=3/2 (k=2 SU(2) WZW model) at the
Takhtajan-Babujian point to c=1 (k=1 SU(2) WZW model), we calculate the
conformal anomaly c and scaling dimensions of the primary fields on the
transition line.Comment: 10 pages, 8 figure
Recursion Relations in Liouville Gravity coupled to Ising Model satisfying Fusion Rules
The recursion relations of 2D quantum gravity coupled to the Ising model
discussed by the author previously are reexamined. We study the case in which
the matter sector satisfies the fusion rules and only the primary operators
inside the Kac table contribute. The theory involves unregularized divergences
in some of correlators. We obtain the recursion relations which form a closed
set among well-defined correlators on sphere, but they do not have a beautiful
structure that the bosonized theory has and also give an inconsistent result
when they include an ill-defined correlator with the divergence. We solve them
and compute the several normalization independent ratios of the well-defined
correlators, which agree with the matrix model results.Comment: Latex, 22 page
Berezinskii-Kosterlitz-Thouless Transition of Spin-1 XXZ Chains in a Staggered Magnetic Field
Phase diagram of S=1 XXZ chain in a staggered magnetic field is obtained
numerically. The Berezinskii-Kosterlitz-Thouless transition between the XY and
the antiferromagnetic phases is studied by the level-spectroscopy. Moreover we
find that there is no distinction between the Haldane and the antiferromagnetic
phases, since the Gaussian critical line does not appear, in contrast to the
case. It is expected that some hidden symmetry breaking
happens not only in the Haldane phase but also in the antiferromagnetic one.Comment: 4 pages, LaTex(JPSJstyle), 8 figures, to appear in J.Phys.Soc.Jp
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