12,053 research outputs found
Exclusive production in proton-proton collisions in the resonance model
The exclusive meson production in proton-proton reactions is
calculated within the resonance model. The considered model was already
successfully applied to the description of , , , ,
production in proton-proton collisions. The only new parameter
entering into the model is the mixing angle which
is taken equal to .Comment: 7 pages, 1 figure, to appear in the brief report section of PR
Cohomology of acting on the space of bilinear differential operators on the superspace
We compute the first cohomology of the ortosymplectic Lie superalgebra
on the (1,1)-dimensional real superspace with
coefficients in the superspace of bilinear
differential operators acting on weighted densities. This work is the simplest
superization of a result by Bouarroudj [Cohomology of the vector fields Lie
algebras on acting on bilinear differential operators,
International Journal of Geometric Methods in Modern Physics
(2005), {\bf 2}; N 1, 23-40]
Medium modifications of kaons in pion matter
Kaon in-medium masses and mean-field potentials are calculated in
isotopically symmetric pion matter to one loop of chiral perturbation theory.
The results are extended to RHIC temperatures using experimental data on scattering phase shifts. The kaon in-medium broadening results in an
acceleration of the decay. The increased apparent dilepton
branching of the -mesons, observed recently by NA50, NA49, and the
PHENIX collaborations at RHIC, is interpreted in terms of rescattering of
secondary kaons inside of the pion matter.Comment: 5 pages, 2 figures, revised version accepted for publication in PR
Symmetries of modules of differential operators
Let be the space of tensor densities of degree (or
weight) on the circle . The space of -th order linear differential operators from
to is a natural module over
, the diffeomorphism group of . We determine the
algebra of symmetries of the modules , i.e.,
the linear maps on commuting with the
-action. We also solve the same problem in the case of
straight line (instead of ) and compare the results in the
compact and non-compact cases.Comment: 29 pages, LaTeX, 4 figure
Ghost story. III. Back to ghost number zero
After having defined a 3-strings midpoint-inserted vertex for the bc system,
we analyze the relation between gh=0 states (wedge states) and gh=3 midpoint
duals. We find explicit and regular relations connecting the two objects. In
the case of wedge states this allows us to write down a spectral decomposition
for the gh=0 Neumann matrices, despite the fact that they are not commuting
with the matrix representation of K1. We thus trace back the origin of this
noncommutativity to be a consequence of the imaginary poles of the wedge
eigenvalues in the complex k-plane. With explicit reconstruction formulas at
hand for both gh=0 and gh=3, we can finally show how the midpoint vertex avoids
this intrinsic noncommutativity at gh=0, making everything as simple as the
zero momentum matter sector.Comment: 40 pages. v2: typos and minor corrections, presentation improved in
sect. 4.3, plots added in app. A.1, two refs added. To appear in JHE
Quantum criticality and minimal conductivity in graphene with long-range disorder
We consider the conductivity of graphene with negligible
intervalley scattering at half filling. We derive the effective field theory,
which, for the case of a potential disorder, is a symplectic-class
-model including a topological term with . As a
consequence, the system is at a quantum critical point with a universal value
of the conductivity of the order of . When the effective time reversal
symmetry is broken, the symmetry class becomes unitary, and
acquires the value characteristic for the quantum Hall transition.Comment: 4 pages, 1 figur
Ghost story. II. The midpoint ghost vertex
We construct the ghost number 9 three strings vertex for OSFT in the natural
normal ordering. We find two versions, one with a ghost insertion at z=i and a
twist-conjugate one with insertion at z=-i. For this reason we call them
midpoint vertices. We show that the relevant Neumann matrices commute among
themselves and with the matrix representing the operator K1. We analyze the
spectrum of the latter and find that beside a continuous spectrum there is a
(so far ignored) discrete one. We are able to write spectral formulas for all
the Neumann matrices involved and clarify the important role of the integration
contour over the continuous spectrum. We then pass to examine the (ghost) wedge
states. We compute the discrete and continuous eigenvalues of the corresponding
Neumann matrices and show that they satisfy the appropriate recursion
relations. Using these results we show that the formulas for our vertices
correctly define the star product in that, starting from the data of two ghost
number 0 wedge states, they allow us to reconstruct a ghost number 3 state
which is the expected wedge state with the ghost insertion at the midpoint,
according to the star recursion relation.Comment: 60 pages. v2: typos and minor improvements, ref added. To appear in
JHE
The Lie Algebraic Significance of Symmetric Informationally Complete Measurements
Examples of symmetric informationally complete positive operator valued
measures (SIC-POVMs) have been constructed in every dimension less than or
equal to 67. However, it remains an open question whether they exist in all
finite dimensions. A SIC-POVM is usually thought of as a highly symmetric
structure in quantum state space. However, its elements can equally well be
regarded as a basis for the Lie algebra gl(d,C). In this paper we examine the
resulting structure constants, which are calculated from the traces of the
triple products of the SIC-POVM elements and which, it turns out, characterize
the SIC-POVM up to unitary equivalence. We show that the structure constants
have numerous remarkable properties. In particular we show that the existence
of a SIC-POVM in dimension d is equivalent to the existence of a certain
structure in the adjoint representation of gl(d,C). We hope that transforming
the problem in this way, from a question about quantum state space to a
question about Lie algebras, may help to make the existence problem tractable.Comment: 56 page
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