768 research outputs found
Parton showers as sources of energy-momentum deposition in the QGP and their implication for shockwave formation at RHIC and at the LHC
We derive the distribution of energy and momentum transmitted from a primary
fast parton and its medium-induced bremsstrahlung gluons to a thermalized
quark-gluon plasma. Our calculation takes into account the important and thus
far neglected effects of quantum interference between the resulting color
currents. We use our result to obtain the rate at which energy is absorbed by
the medium as a function of time and find that the rate is modified by the
quantum interference between the primary parton and secondary gluons. This
Landau-Pomeranchuk-Migdal type interference persists for time scales relevant
to heavy ion phenomenology. We further couple the newly derived source of
energy and momentum deposition to linearized hydrodynamics to obtain the bulk
medium response to realistic parton propagation and splitting in the
quark-gluon plasma. We find that because of the characteristic large angle
in-medium gluon emission and the multiple sources of energy deposition in a
parton shower, formation of well defined Mach cones by energetic jets in heavy
ion reactions is not likely.Comment: 8 pages, 4 figure
Liouville theory and uniformization of four-punctured sphere
Few years ago Zamolodchikov and Zamolodchikov proposed an expression for the
4-point classical Liouville action in terms of the 3-point actions and the
classical conformal block. In this paper we develop a method of calculating the
uniformizing map and the uniformizing group from the classical Liouville action
on n-punctured sphere and discuss the consequences of Zamolodchikovs conjecture
for an explicit construction of the uniformizing map and the uniformizing group
for the sphere with four punctures.Comment: 17 pages, no figure
Meson Production in Proton-Proton Collisions in the Naive Non-Abelianization Approximation and the Role of Infrared Renormalons
We calculate the "naive non-abelianization" (NNA) contributions of the
higher-twist Feynman diagrams to the large- inclusive pion production
cross section in proton-proton collisions in the case of the running coupling
and frozen coupling approaches. We compare the resummed "naive
non-abelianization" higher-twist cross sections with the ones obtained in the
framework of the frozen coupling approach and leading-twist cross section. The
structure of infrared renormalon singularities of the higher twist subprocess
cross section and it's resummed expression are found. We discuss the
phenomenological consequences of possible higher-twist contributions to the
pion production in proton-proton collisions in within NNA.Comment: 17 pages, 9 figure
New solutions of Heun general equation
We show that in four particular cases the derivative of the solution of Heun
general equation can be expressed in terms of a solution to another Heun
equation. Starting from this property, we use the Gauss hypergeometric
functions to construct series solutions to Heun equation for the mentioned
cases. Each of the hypergeometric functions involved has correct singular
behavior at only one of the singular points of the equation; the sum, however,
has correct behavior
The ground state energy of a massive scalar field in the background of a semi-transparent spherical shell
We calculate the zero point energy of a massive scalar field in the
background of an infinitely thin spherical shell given by a potential of the
delta function type. We use zeta functional regularization and express the
regularized ground state energy in terms of the Jost function of the related
scattering problem. Then we find the corresponding heat kernel coefficients and
perform the renormalization, imposing the normalization condition that the
ground state energy vanishes when the mass of the quantum field becomes large.
Finally the ground state energy is calculated numerically. Corresponding plots
are given for different values of the strength of the background potential, for
both attractive and repulsive potentials.Comment: 15 pages, 5 figure
Propagation of leaky surface waves on contact magnetohydrodynamic discontinuities in incompressible plasmas
We study the wave propagation on a magnetohydrodynamic contact discontinuity. Using the Laplace transform, we obtain the solution to the initial value problem describing the evolution of a perturbation of the discontinuity. We use this solution to study the leaky modes that determine the asymptotic behaviour of the solution for large time. We find the approximate expressions describing the leaky modes for a small inclination angle of the magnetic field. We also discuss the transition to the tangential discontinuity as the inclination angle tends to zero. We show that there is no continuous transition from the leaky modes on a contact discontinuity to the surface modes on a tangential discontinuity. However, such a transition exists if we take the average quantities describing the leaky modes
Relationship and Network Approach to Innovation and Capabilities Building in Small and Medium-Sized UK Organic Food and Drink Suppliers: A Literature Review
Both business and consumer markets of food and drink are increasingly changing, concomitant with changing consumer habits and lifestyles. Particularly in industrialised countries, there has been a tremendous growth in consumer interest for organic food in the last fifteen years, largely driven by the need for healthy food. These market changes have implications for the way firms in the food and
drink industry conduct their business. Nevertheless, unlike large firms, small suppliers tend to be constrained in terms of innovations and capabilities, for instance to enable them keep pace with market changes. Based on the literature review, this paper develops a framework that suggests that market-driven innovations may be developed and implemented through augmentation of small and
medium-sized suppliers’ (SMEs) own capabilities with those of their larger customers. This consequently would enable SMEs to keep pace with market changes and hence sustain their survival
Hyperspherical harmonics with arbitrary arguments
The derivation scheme for hyperspherical harmonics (HSH) with arbitrary
arguments is proposed. It is demonstrated that HSH can be presented as the
product of HSH corresponding to spaces with lower dimensionality multiplied by
the orthogonal (Jacobi or Gegenbauer) polynomial. The relation of HSH to
quantum few-body problems is discussed. The explicit expressions for
orthonormal HSH in spaces with dimensions from 2 to 6 are given. The important
particular cases of four- and six-dimensional spaces are analyzed in detail and
explicit expressions for HSH are given for several choices of hyperangles. In
the six-dimensional space, HSH representing the kinetic energy operator
corresponding to i) the three-body problem in physical space and ii) four-body
planar problem are derived.Comment: 18 pages, 1 figur
Critical properties and Bose Einstein Condensation in dimer spin systems
We analyze the spin relaxation time for a system made of weakly
coupled one dimensional ladders.This system allows to probe the dimensional
crossover between a Luttinger liquid and a Bose-Einstein condensateof magnons.
We obtain the temperature dependence of in the various dimensional
regimes, and discuss the experimental consequences.Comment: 4 pages, RevTeX 4, 3 EPS figure
The decay b -> s g at NLL in the Standard Model
I present the Standard Model calculation of the decay rate for b -> s g (g
denotes a gluon) at next-to-leading logarithms (NLL). In order to get a
meaningful physical result, the decay b -> s g g and certain contributions of b
-> s \bar{f} f (where f are the light quark flavours u, d and s) have to be
included as well. Numerically we get BR^(NLL) = (5.0 +/- 1.0) * 10^{-3} which
is more than a factor 2 larger than the leading logarithmic result BR^(LL) =
(2.2 +/- 0.8) * 10^{-3}. Further, I consider the impact of this contribution on
the charmless hadronic branching ratio BRc, which could be used to extract the
CKM-ratio |V_(ub)/V_(cb)| with more accuracy. Finally, I have a short look at
BRc in scenarios where the Wilson coefficient C_8 is enhanced by new physics.Comment: 7 pages including 5 postscript figures; uses epsfi
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