2,274 research outputs found
On the energy-shell contributions of the three-particle~-~ three-hole excitations
The response functions for the extended second and third random phase
approximation are compared. A second order perturbation calculation shows that
the first-order amplitude for the direct excitation from the ground
state cancels with those that are engendered by the - coupling. As
a consequence nonvanishing effects to the response involve off
energy shell renormalization only. On shell processes are absent.Comment: 12 pages text (LaTex) and 1 figure included, to be published in Phys.
Rev.
Momentum Distribution in Nuclear matter within a Perturbation Approximation
It is shown that the norm corrections, introduced to avoid the violation of
the constraints on the depletion of the hole states in the standard
perturbative 2p2h approach, leads in nuclear matter to a dependence of the
momentum distribution with the total nucleon number. This unphysical behavior,
which in turn makes the depletion to be non-extensive, arises from
contributions of disconnected diagrams contained in the norm. It is found that
the extensivity is again recovered when the 4p4h excitations in the ground
state are included, and a reasonable value for the total number of nucleons
promoted above the Fermi level is obtained.Comment: 11 pages, LaTeX, 5 figures, figures 1 to 3 included in the latex
file, postscript files of figures 4 and 5 available from the Authors.
Accepted for publication in Phys. Rev.
Notes on S-Matrix of Non-critical N=2 String
In this paper we discuss the scattering S-matrix of non-critical N=2 string
at tree level. First we consider the \hat{c}<1 string defined by combining the
N=2 time-like linear dilaton SCFT with the N=2 Liouville theory. We compute
three particle scattering amplitudes explicitly and find that they are actually
vanishing. We also find an evidence that this is true for higher amplitudes.
Next we analyze another \hat{c}<1 string obtained from the N=2 time-like
Liouville theory, which is closely related to the N=2 minimal string. In this
case, we find a non-trivial expression for the three point functions. When we
consider only chiral primaries, the amplitudes are very similar to those in the
(1,n) non-critical bosonic string.Comment: 27 pages, harvmac, section 5 modified: a relation to (1,n)
non-critical bosonic string adde
On the Connection between N=2 Minimal String and (1,n) Bosonic Minimal String
We study the scattering amplitudes in the N=2 minimal string or equivalently
in the N=4 topological string on ALE spaces. We find an interesting connection
between the tree level amplitudes of the N=2 minimal string and those of the
(1,n) minimal bosonic string. In particular we show that the four and
five-point functions of the N=2 string can be directly rewritten in terms of
those of the latter theory. This relation offers a map of physical states
between these two string theories. Finally we propose a possible matrix model
dual for the N=2 minimal string in the light of this connection.Comment: 40 pages, one figure, harvmac, minor corrections, references adde
A holographic proof of the strong subadditivity of entanglement entropy
When a quantum system is divided into subsystems, their entanglement
entropies are subject to an inequality known as "strong subadditivity". For a
field theory this inequality can be stated as follows: given any two regions of
space and , . Recently, a
method has been found for computing entanglement entropies in any field theory
for which there is a holographically dual gravity theory. In this note we give
a simple geometrical proof of strong subadditivity employing this holographic
prescription.Comment: 9 pages, 3 figure
Analysis of exchange terms in a projected ERPA Theory applied to the quasi-elastic (e,e') reaction
A systematic study of the influence of exchange terms in the longitudinal and
transverse nuclear response to quasi-elastic (e,e') reactions is presented. The
study is performed within the framework of the extended random phase
approximation (ERPA), which in conjuction with a projection method permits a
separation of various contributions tied to different physical processes. The
calculations are performed in nuclear matter up to second order in the residual
interaction for which we take a (pi+rho)-model with the addition of the
Landau-Migdal g'-parameter. Exchange terms are found to be important only for
the RPA-type contributions around the quasielastic peak.Comment: 29 pages, 6 figs (3 in postscript, 3 faxed on request), epsf.st
D-Brane Probe and Closed String Tachyons
We consider a D-brane probe in unstable string background associated with
flux branes. The twist in spacetime metric reponsible for the supersymmetry
breaking is shown to manifest itself in mixing of open Wilson lines with the
phases of some adjoint matter fields, resulting in a nonlocal and
nonsupersymmetric form of Yang-Mills theory as the probe dynamics. This
provides a setup where one can study fate of a large class of unstable closed
string theories that include as a limit type 0 theories and various orbifolds
of type II and type 0 theories. We discuss the limit of orbifold
in some detail and speculate on couplings with closed string tachyons.Comment: LaTeX, 17 pages, typos fixed, references update
Ultracold collisions between two light indistinguishable diatomic molecules: elastic and rotational energy transfer in HD+HD
A close coupling quantum-mechanical calculation is performed for rotational
energy transfer in a HD+HD collision at very low energy, down to the ultracold
temperatures: K. A global six-dimensional H-H
potential energy surface is adopted from a previous work [Boothroyd {\it et
al.}, J. Chem. Phys., {\bf 116}, 666 (2002).] State-resolved integral cross
sections of different
quantum-mechanical rotational transitions in the HD
molecules and corresponding state-resolved thermal rate coefficients
have been computed. Additionally, for comparison,
H+H calculations for a few selected rotational transitions have also
been performed. The hydrogen and deuterated hydrogen molecules are treated as
rigid rotors in this work. A pronounced isotope effect is identified in the
cross sections of these collisions at low and ultracold temperatures.Comment: 9 pages, 9 figures. Accepted for publication in Physical Review
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