Implicit Solutions of PDE's

Further investigations of implicit solutions to non-linear partial differential equations are pursued. Of particular interest are the equations which are Lorentz invariant. The question of which differential equations of second order for a single unknown $\phi$ are solved by the imposition of an inhomogeneous quadratic relationship among the independent variables, whose coefficients are functions of $\phi$ is discussed, and it is shown that if the discriminant of the quadratic vanishes, then an implicit solution of the so-called Universal Field Equation is obtained. The relation to the general solution is discussed.Comment: 11 pages LaTeX2

Elliptic Flow, Initial Eccentricity and Elliptic Flow fluctuations in Heavy Ion Collisions at RHIC

We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the initial collision geometry is translated into the final state azimuthal particle distribution, leading to an event-by-event proportionality between the observed elliptic flow and initial eccentricity.Comment: To appear in the proceedings of the Lake Louise Winter Institute 2007. The proceedings of the institute will be published by World Scientifi

Lattice renormalisation of O(a) improved heavy-light operators

The analytical expressions and the numerical values of the renormalisation constants of ${\cal O}(a)$ improved static-light currents are given at one-loop order of perturbation theory in the framework of Heavy Quark Effective Theory: the static quark is described by the HYP action and the light quark is described either with the Clover or the Neuberger action. These factors are relevant to extract from a lattice computation the decay constants $f_B$, $f_{B_S}$ and the set of bag parameters $B_i$ associated with $B-\bar{B}$ mixing phenomenology in the Standard Model and beyond.Comment: 16 pages, 2 figures, 4 tables; few comments and references added; version to be published in Phys Rev

Exact calculation of the ground-state dynamical spin correlation function of a S=1/2 antiferromagnetic Heisenberg chain with free spinons

We calculate the exact dynamical magnetic structure factor S(Q,E) in the ground state of a one-dimensional S=1/2 antiferromagnet with gapless free S=1/2 spinon excitations, the Haldane-Shastry model with inverse-square exchange, which is in the same low-energy universality class as Bethe's nearest-neighbor exchange model. Only two-spinon excited states contribute, and S(Q,E) is found to be a very simple integral over these states.Comment: 11 pages, LaTeX, RevTeX 3.0, cond-mat/930903

The space-time structure of hard scattering processes

Recent studies of exclusive electroproduction of vector mesons at JLab make it possible for the first time to play with two independent hard scales: the virtuality Q^2 of the photon, which sets the observation scale, and the momentum transfer t to the hadronic system, which sets the interaction scale. They reinforce the description of hard scattering processes in terms of few effective degrees of freedom relevant to the Jlab-Hermes energy range.Comment: 4 pages; 5 figure