3,960 research outputs found
Color symmetrical superconductivity in a schematic nuclear quark model
In this note, a novel BCS-type formalism is constructed in the framework of a
schematic QCD inspired quark model, having in mind the description of color
symmetrical superconducting states. The physical properties of the BCS vacuum
(average numbers of quarks of different colors) remain unchanged under an
arbitrary color rotation. In the usual approach to color superconductivity, the
pairing correlations affect only the quasi-particle states of two colors, the
single particle states of the third color remaining unaffected by the pairing
correlations. In the theory of color symmetrical superconductivity here
proposed, the pairing correlations affect symmetrically the quasi-particle
states of the three colors and vanishing net color-charge is automatically
insured. It is found that the groundstate energy of the color symmetrical
sector of the Bonn model is well approximated by the average energy of the
color symmetrical superconducting state proposed here
Neutron Skin Thickness of 90Zr Determined By Charge Exchange Reactions
Charge exchange spin-dipole (SD) excitations of 90Zr are studied by the
90Zr(p,n) and 90Zr(n,p) reactions at 300 MeV. A multipole decomposition
technique is employed to obtain the SD strength distributions in the cross
section spectra. For the first time, a model-independent SD sum rule value is
obtained: 148+/-12 fm^2. The neutron skin thickness of 90Zr is determined to be
0.07+/-0.04 fm from the SD sum rule value.Comment: 4 pages, 2 figures, submitted to Phys. Rev.
Complementarity and Scientific Rationality
Bohr's interpretation of quantum mechanics has been criticized as incoherent
and opportunistic, and based on doubtful philosophical premises. If so Bohr's
influence, in the pre-war period of 1927-1939, is the harder to explain, and
the acceptance of his approach to quantum mechanics over de Broglie's had no
reasonable foundation. But Bohr's interpretation changed little from the time
of its first appearance, and stood independent of any philosophical
presuppositions. The principle of complementarity is itself best read as a
conjecture of unusually wide scope, on the nature and future course of
explanations in the sciences (and not only the physical sciences). If it must
be judged a failure today, it is not because of any internal inconsistency.Comment: 29 page
The Complete KLT-Map Between Gravity and Gauge Theories
We present the complete map of any pair of super Yang-Mills theories to
supergravity theories as dictated by the KLT relations in four dimensions.
Symmetries and the full set of associated vanishing identities are derived. A
graphical method is introduced which simplifies counting of states, and helps
in identifying the relevant set of symmetries.Comment: 41 pages, 16 figures, published version, typos corrected, references
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Directed Percolation Universality in Asynchronous Evolution of Spatio-Temporal Intermittency
We present strong evidence that a coupled-map-lattice model for
spatio-temporal intermittency belongs to the universality class of directed
percolation when the updating rules are asynchronous, i.e. when only one
randomly chosen site is evolved at each time step. In contrast, when the system
is subjected to parallel updating, available numerical evidence suggests that
it does not belong to this universality class and that it is not even
universal. We argue that in the absence of periodic external forcing, the
asynchronous rule is the more physical.Comment: 12 pages, RevTeX, includes 6 figures, submitted to Physical Review
Letters; changed version includes a better physical motivation for
asynchronous updates, extra references and minor change
New Bardeen-Cooper-Schrieffer-type theory at finite temperature with particle-number conservation
We formulate a new Bardeen-Cooper-Schrieffer (BCS)-type theory at finite
temperature, by deriving a set of variational equations of the free energy
after the particle-number projection. With its broad applicability, this theory
can be a useful tool for investigating the pairing phase transition in finite
systems with the particle-number conservation. This theory provides effects of
the symmetry-restoring fluctuation (SRF) for the pairing phenomena in finite
fermionic systems, distinctively from those of additional quantum fluctuations.
It is shown by numerical calculations that the phase transition is compatible
with the conservation in this theory, and that the SRF shifts up the critical
temperature (). This shift of occurs due to
reduction of degrees-of-freedom in canonical ensembles, and decreases only
slowly as the particle-number increases (or as the level spacing narrows), in
contrast to the conventional BCS theory.Comment: 10 pages including 3 figures, to be published in Phys. Rev.
New Identities among Gauge Theory Amplitudes
Color-ordered amplitudes in gauge theories satisfy non-linear identities
involving amplitude products of different helicity configurations. We consider
the origin of such identities and connect them to the Kawai-Lewellen-Tye (KLT)
relations between gravity and gauge theory amplitudes. Extensions are made to
one-loop order of the full N=4 super Yang-Mills multiplet.Comment: 7 page
Bursts and Shocks in a Continuum Shell Model
We study a "burst" event, i. e. the evolution of an initial condition having
support only in a finite interval of k-space, in the continuum shell model due
to Parisi. We show that the continuum equation without forcing or dissipation
can be explicitly written in characteristic form and that the right and left
moving parts can be solved exactly. When this is supplemented by the
appropriate shock condition it is possible to find the asymptotic form of the
burst.Comment: 15 pages, 2 eps figures included, Latex 2e. Contribution to the
proceedings of the conference: Disorder and Chaos, in honour of Giovanni
Paladin, September 22-24, 1997, in Rom
On the relation between models and the interacting boson model
The connections between the models (the original E(5) using an
infinite square well, , and ), based
on particular solutions of the geometrical Bohr Hamiltonian with
-unstable potentials, and the interacting boson model (IBM) are
explored. For that purpose, the general IBM Hamiltonian for the
transition line is used and a numerical fit to the different models
energies is performed, later on the obtained wavefunctions are used to
calculate B(E2) transition rates. It is shown that within the IBM one can
reproduce very well all these models. The agreement is the best for
and reduces when passing through ,
and E(5), where the worst agreement is obtained (although still very good for a
restricted set of lowest lying states). The fitted IBM Hamiltonians correspond
to energy surfaces close to those expected for the critical point. A phenomenon
similar to the quasidynamical symmetry is observed
Effects of particle-number conservation on heat capacity of nuclei
By applying the particle-number projection to the finite-temperature BCS
theory, the -shaped heat capacity, which has recently been claimed to be a
fingerprint of the superfluid-to-normal phase transition in nuclei, is
reexamined. It is found that the particle-number (or number-parity) projection
gives -shapes in the heat capacity of nuclei which look qualitatively
similar to the observed ones. These -shapes are accounted for as effects of
the particle-number conservation on the quasiparticle excitations, and occur
even when we keep the superfluidity at all temperatures by assuming a constant
gap in the BCS theory. The present study illustrates significance of the
conservation laws in studying phase transitions of finite systems.Comment: RevTeX4, 12 pages including 5 figures (1 color figure), to be
published in PR
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