113 research outputs found
Pionic Modes Studied by Quasielastic (\vec{p}, \vec{n}) Reactions
It has long been expected that the pionic modes show some collective
phenomena such as the pion condensation in the high density nuclear matter and
its precursor phenomena in the ordinary nuclei. Here we show an evidence of the
precursor observed in the isovector spin longitudinal cross sections ID_q of
the quasielastic 12C, 40Ca (\vec{p}, \vec{n}) reactions at T_p = 346 and 494MeV
with the momentum transfer q = 1.7fm-1. Another aim of this report is to
evaluate the Landau-Migdal parameters g'_{NN}, g'_{N\Delta} and
g'_{\Delta\Delta} at the large momentum region from the above reactions. We
obtained g'_{NN} \approx 0.6-0.7, g'_{N\Delta} \approx 0.3-0.4. The results are
consistent with those at the small momentum region, which are obtained from the
Gamov-Teller strength distribution.Comment: 6 pages, 4 figures, proceedings for 7th International Spring Seminar
on Nuclear Physics "Challenges of Nuclear Structure" at Maiori, Ital
How to remove the boundary in CFT - an operator algebraic procedure
The relation between two-dimensional conformal quantum field theories with
and without a timelike boundary is explored.Comment: 18 pages, 2 figures. v2: more precise title, reference correcte
Representations of Conformal Nets, Universal C*-Algebras and K-Theory
We study the representation theory of a conformal net A on the circle from a
K-theoretical point of view using its universal C*-algebra C*(A). We prove that
if A satisfies the split property then, for every representation \pi of A with
finite statistical dimension, \pi(C*(A)) is weakly closed and hence a finite
direct sum of type I_\infty factors. We define the more manageable locally
normal universal C*-algebra C*_ln(A) as the quotient of C*(A) by its largest
ideal vanishing in all locally normal representations and we investigate its
structure. In particular, if A is completely rational with n sectors, then
C*_ln(A) is a direct sum of n type I_\infty factors. Its ideal K_A of compact
operators has nontrivial K-theory, and we prove that the DHR endomorphisms of
C*(A) with finite statistical dimension act on K_A, giving rise to an action of
the fusion semiring of DHR sectors on K_0(K_A)$. Moreover, we show that this
action corresponds to the regular representation of the associated fusion
algebra.Comment: v2: we added some comments in the introduction and new references.
v3: new authors' addresses, minor corrections. To appear in Commun. Math.
Phys. v4: minor corrections, updated reference
Thermal States in Conformal QFT. II
We continue the analysis of the set of locally normal KMS states w.r.t. the
translation group for a local conformal net A of von Neumann algebras on the
real line. In the first part we have proved the uniqueness of KMS state on
every completely rational net. In this second part, we exhibit several
(non-rational) conformal nets which admit continuously many primary KMS states.
We give a complete classification of the KMS states on the U(1)-current net and
on the Virasoro net Vir_1 with the central charge c=1, whilst for the Virasoro
net Vir_c with c>1 we exhibit a (possibly incomplete) list of continuously many
primary KMS states. To this end, we provide a variation of the
Araki-Haag-Kastler-Takesaki theorem within the locally normal system framework:
if there is an inclusion of split nets A in B and A is the fixed point of B
w.r.t. a compact gauge group, then any locally normal, primary KMS state on A
extends to a locally normal, primary state on B, KMS w.r.t. a perturbed
translation. Concerning the non-local case, we show that the free Fermi model
admits a unique KMS state.Comment: 36 pages, no figure. Dedicated to Rudolf Haag on the occasion of his
90th birthday. The final version is available under Open Access. This paper
contains corrections to the Araki-Haag-Kaster-Takesaki theorem (and to a
proof of the same theorem in the book by Bratteli-Robinson). v3: a reference
correcte
Two-step contribution to the spin-longitudinal and spin-transverse cross sections of the quasielastic (p,n) reactions
The two-step contribution to the spin-longitudinal and the spin-transverse
cross sections of ^{12}C,^{40}Ca(p,n) reactions at 494 MeV and 346 MeV is
calculated. We use a plane-wave approximation and evaluate the relative
contributions from the one-step and the two-step processes. We found that the
ratios of the two-step to the one-step processes are larger in the
spin-transverse cross sections than in the spin-longitudinal ones. Combining
these results with the distorted-wave impulse approximation (DWIA) results we
obtained considerable two-step contributions to the spin-longitudinal and the
spin-transverse cross sections. The two-step processes are important in
accounting for the underestimation of the DWIA results for the
spin-longitudinal and the spin-transverse cross sections.Comment: LaTeX 11 pages, 10 figure
Algebraic conformal quantum field theory in perspective
Conformal quantum field theory is reviewed in the perspective of Axiomatic,
notably Algebraic QFT. This theory is particularly developped in two spacetime
dimensions, where many rigorous constructions are possible, as well as some
complete classifications. The structural insights, analytical methods and
constructive tools are expected to be useful also for four-dimensional QFT.Comment: Review paper, 40 pages. v2: minor changes and references added, so as
to match published versio
An algebraic Haag's theorem
Under natural conditions (such as split property and geometric modular action
of wedge algebras) it is shown that the unitary equivalence class of the net of
local (von Neumann) algebras in the vacuum sector associated to double cones
with bases on a fixed space-like hyperplane completely determines an algebraic
QFT model. More precisely, if for two models there is unitary connecting all of
these algebras, then --- without assuming that this unitary also connects their
respective vacuum states or spacetime symmetry representations --- it follows
that the two models are equivalent. This result might be viewed as an algebraic
version of the celebrated theorem of Rudolf Haag about problems regarding the
so-called "interaction-picture" in QFT.
Original motivation of the author for finding such an algebraic version came
from conformal chiral QFT. Both the chiral case as well as a related conjecture
about standard half-sided modular inclusions will be also discussed
Noninteraction of waves in two-dimensional conformal field theory
In higher dimensional quantum field theory, irreducible representations of
the Poincare group are associated with particles. Their counterpart in
two-dimensional massless models are "waves" introduced by Buchholz. In this
paper we show that waves do not interact in two-dimensional Moebius covariant
theories and in- and out-asymptotic fields coincide. We identify the set of the
collision states of waves with the subspace generated by the chiral components
of the Moebius covariant net from the vacuum. It is also shown that
Bisognano-Wichmann property, dilation covariance and asymptotic completeness
(with respect to waves) imply Moebius symmetry.
Under natural assumptions, we observe that the maps which give asymptotic
fields in Poincare covariant theory are conditional expectations between
appropriate algebras. We show that a two-dimensional massless theory is
asymptotically complete and noninteracting if and only if it is a chiral
Moebius covariant theory.Comment: 28 pages, no figur
On local boundary CFT and non-local CFT on the boundary
The holographic relation between local boundary conformal quantum field
theories (BCFT) and their non-local boundary restrictions is reviewed, and
non-vacuum BCFT's, whose existence was conjectured previously, are constructed.Comment: 16 pages. Contribution to "Rigorous Quantum Field Theory", Symposium
in honour of J. Bros, Paris, July 2004. Based on joint work math-ph/0405067
with R. Long
Asymptotic completeness for infraparticles in two-dimensional conformal field theory
We formulate a new concept of asymptotic completeness for two-dimensional
massless quantum field theories in the spirit of the theory of particle
weights. We show that this concept is more general than the standard particle
interpretation based on Buchholz' scattering theory of waves. In particular, it
holds in any chiral conformal field theory in an irreducible product
representation and in any completely rational conformal field theory. This
class contains theories of infraparticles to which the scattering theory of
waves does not apply.Comment: 17 pages, no figur
- …