Factorization in Semi-Inclusive Polarized Deep Inelastic Scattering

We calculate and analize the ${\cal{O}}(\alpha_s)$ one-particle inclusive cross section in polarized deep inelastic lepton-hadron scattering, using dimensional regularization and the HVBM prescription for $\gamma_5$. We discuss the factorization of all the collinear singularities related to the process, particularly those which are absorbed in the redefinition of the spin dependent analogue of the recently introduced fracture functions. This is done in the usual $\overline{MS}$ scheme and in another one, called $\overline{MS_p}$, which factorizes soft contributions and guarantees the axial current (non)conservation properties.Comment: 16 pages, figures included using FEYNMAN macr

Realising the Olympic dream: vision, support and challenge

The sporting arena is replete with examples and anecdotes of great inspirational coaches that have led teams to success, often in the face of adversity and against seemingly better opponents. The role of the coach in developing and motivating athletes has also been the focus of much research in sport psychology (e.g., Challaduria 1990; Smith & Smoll, 2007). Despite the ease with which one readily accepts that coaches can be inspirational, the sport coaching literature is somewhat devoid of research on inspirational coaches and the effects of such coaches on athletic success. The purpose of the current paper is to theoretically delineate the inspirational effects of coaches in sport. Given the relative paucity of inspiration-related research in sport we draw upon contemporary theories of leadership from organisational and military psychology (e.g., transformational and charismatic leadership theories). We propose a sport-specific model of leadership that centres around the vision, support, and challenge meta-cognitive model developed by Arthur and Hardy in military contexts. The model posits that �great� coaches inspire their athletes by: (a) creating an inspirational vision of the future; (b) providing the necessary support to achieve the vision; and (c) providing the challenge to achieve the vision. The underlying proposition is that the vision provides meaning and direction for followers� effort. That is, the vision serves as the beacon around which all the sweat, pain and sacrifice involved in achieving success at the highest level in sport is directed. At the heart of this model is the notion that athletes can achieve their dreams provided they are inspired to do so; this is because all other things being equal the person who is motivated to practice longer and train harder will ultimately be the best. The current paper will delineate the coach�s role in inspiring the athlete to train harder and longer

Massive Electrodynamics and the Magnetic Monopoles

We investigate in detail the problem of constructing magnetic monopole solutions within the finite-range electrodynamics (i.e., electrodynamics with non-zero photon mass, which is the simplest extension of the standard theory; it is fully compatible with the experiment). We first analyze the classical electrodynamics with the additional terms describing the photon mass and the magnetic charge; then we look for a solution analogous to the Dirac monopole solution. Next, we plug the found solution into the Schr\"{o}dinger equation describing the interaction between the the magnetic charge and the electron. After that, we try to derive the Dirac quantization condition for our case. Since gauge invariance is lost in massive electrodynamics, we use the method of angular momentum algebra. Under rather general assumptions we prove the theorem that the construction of such an algebra is not possible and therefore the quantization condition cannot be derived. This points to the conclusion that the Dirac monopole and the finite photon mass cannot coexist within one and the same theory. Some physical consequences of this conclusion are considered. The case of t'Hooft-Polyakov monopole is touched upon briefly.Comment: 24 pages, revtex, 1 figure appended as a PostScript fil

A geometrical estimation of saturation of partonic densities

We propose a new criterium for saturation of the density of partons both in nucleons and nuclei. It is applicable to any multiple scattering model which would be used to compute the number of strings exchanged in $ep$ and $eA$ collisions. The criterium is based on percolation of strings, and the onset of percolation is estimated from expectations coming from the study of heavy ion collisions at high energies. We interpret this onset as an indication of saturation of the density of partons in the wave function of the hadron. In order to produce quantitative results, a particular model fitted to describe present HERA data and generalized to the nuclear case is used. Nevertheless, with the number of scatterings controlled by the relation between inclusive and diffractive processes, conclusions are weakly model-dependent as long as different models are tuned to describe the experimental data. This constitutes a new approach, based on the eikonal description of soft hadronic collisions, and different from others which employ either perturbative QCD ideas or semiclassical methods. It offers an alternative picture for saturation in the small $Q^2$ region.Comment: LaTeX, 15 pages, 2 eps figures included using epsfig; final version, abstract and discussions enlarged, references added and updated, results unchanged; more references adde

The critical Ising model via Kac-Ward matrices

The Kac-Ward formula allows to compute the Ising partition function on any finite graph G from the determinant of 2^{2g} matrices, where g is the genus of a surface in which G embeds. We show that in the case of isoradially embedded graphs with critical weights, these determinants have quite remarkable properties. First of all, they satisfy some generalized Kramers-Wannier duality: there is an explicit equality relating the determinants associated to a graph and to its dual graph. Also, they are proportional to the determinants of the discrete critical Laplacians on the graph G, exactly when the genus g is zero or one. Finally, they share several formal properties with the Ray-Singer \bar\partial-torsions of the Riemann surface in which G embeds.Comment: 30 pages, 10 figures; added section 4.4 in version

A note on the Sagnac effect and current terrestrial experiments

We focus on the Sagnac effect for light beams in order to evaluate if the higher-order relativistic corrections of kinematic origin could be relevant for actual terrestrial experiments. Moreover, we discuss to what extent the analogy with the Aharonov-Bohm effect holds true in a fully relativistic framework. We show that the analogy with the Aharonov-Bohm is not true in general, but is recovered in a suitable low-order approximation, and that even though the Sagnac effect is influenced by both the position of the interferometer in the rotating frame and its extension, these effects are negligible for current terrestrial experiment

Hermitian K-theory and 2-regularity for totally real number fields

We completely determine the 2-primary torsion subgroups of the hermitian K-groups of rings of 2-integers in totally real 2-regular number fields. The result is almost periodic with period 8. We also identify the homotopy fibers of the forgetful and hyperbolic maps relating hermitian and algebraic K-theory. The result is then exactly periodic of period 8. In both the orthogonal and symplectic cases, we prove the 2-primary hermitian Quillen-Lichtenbaum conjecture.Comment: To appear in Mathematische Annale

Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions

We review the most important experimental results from the first three years of nucleus-nucleus collision studies at RHIC, with emphasis on results from the STAR experiment, and we assess their interpretation and comparison to theory. The theory-experiment comparison suggests that central Au+Au collisions at RHIC produce dense, rapidly thermalizing matter characterized by: (1) initial energy densities above the critical values predicted by lattice QCD for establishment of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by constituent interactions of very short mean free path, established most probably at a stage preceding hadron formation; and (3) opacity to jets. Many of the observations are consistent with models incorporating QGP formation in the early collision stages, and have not found ready explanation in a hadronic framework. However, the measurements themselves do not yet establish unequivocal evidence for a transition to this new form of matter. The theoretical treatment of the collision evolution, despite impressive successes, invokes a suite of distinct models, degrees of freedom and assumptions of as yet unknown quantitative consequence. We pose a set of important open questions, and suggest additional measurements, at least some of which should be addressed in order to establish a compelling basis to conclude definitively that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.

Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV

We report the STAR measurement of Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi spectra and yields are obtained at mid-rapidity for five centrality bins in Au+Au collisions and for non-singly-diffractive p+p collisions. It is found that the Phi transverse momentum distributions from Au+Au collisions are better fitted with a single-exponential while the p+p spectrum is better described by a double-exponential distribution. The measured nuclear modification factors indicate that Phi production in central Au+Au collisions is suppressed relative to peripheral collisions when scaled by the number of binary collisions. The systematics of versus centrality and the constant Phi/K- ratio versus beam species, centrality, and collision energy rule out kaon coalescence as the dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let

Longitudinal scaling property of the charge balance function in Au + Au collisions at 200 GeV

We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at 200 GeV using the STAR detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage [-1.3, 1.3]. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes.Comment: 6 pages, 3 figure