Annihilation contribution and B→a0π,f0KB\to a_0 \pi, f_0 K decays

We analyze the decays $B^0 \to a^\pm_0 \pi^\mp$ and $B^{-,0} \to f_0 K^{-,0}$ and show that within the factorization approximation a phenomenological consistent picture can be obtained. We show that in this approach the $O_6$ operator provides the dominant contributions to the suppressed channel $B^0 \to a^+_0 \pi^-$. When the $a_0$ is considered a two quark state, evaluation of the annihilation form factor using Perturbative $QCD$ implies that this contribution is not negligible, and furthermore it can interfere constructively or destructively with other penguin contributions. As a consequence of this ambiguity, the positive identification of $B^0 \to \pi^+ a_0^-$ can not distinguish between the two or four quark assignment of the $a_0$. According to our calculation, a best candidate to distinguish the nature of $a_0$ scalar is $Br(B^-\to \pi^0a_0^-)$ since the predictions for a four quark model is one order of magnitude smaller than for the two quark assignment. When the scalars are seen as two quarks states, simple theoretical assumptions based on SU(2) isospin symmetry provide relations between different B decays involving one scalar and one pseudoscalar meson.Comment: 12 pages, 3 figure

The stochastic gravitational wave background from turbulence and magnetic fields generated by a first-order phase transition

We analytically derive the spectrum of gravitational waves due to magneto-hydrodynamical turbulence generated by bubble collisions in a first-order phase transition. In contrast to previous studies, we take into account the fact that turbulence and magnetic fields act as sources of gravitational waves for many Hubble times after the phase transition is completed. This modifies the gravitational wave spectrum at large scales. We also model the initial stirring phase preceding the Kolmogorov cascade, while earlier works assume that the Kolmogorov spectrum sets in instantaneously. The continuity in time of the source is relevant for a correct determination of the peak position of the gravitational wave spectrum. We discuss how the results depend on assumptions about the unequal-time correlation of the source and motivate a realistic choice for it. Our treatment gives a similar peak frequency as previous analyses but the amplitude of the signal is reduced due to the use of a more realistic power spectrum for the magneto-hydrodynamical turbulence. For a strongly first-order electroweak phase transition, the signal is observable with the space interferometer LISA.Comment: 46 pages, 17 figures. Replaced with revised version accepted for publication in JCA

Symmetric coupling of four spin-1/2 systems

We address the non-binary coupling of identical angular momenta based upon the representation theory for the symmetric group. A correspondence is pointed out between the complete set of commuting operators and the reference-frame-free subsystems. We provide a detailed analysis of the coupling of three and four spin-1/2 systems and discuss a symmetric coupling of four spin-1/2 systems.Comment: 20 pages, no figure

Order in glassy systems

A directly measurable correlation length may be defined for systems having a two-step relaxation, based on the geometric properties of density profile that remains after averaging out the fast motion. We argue that the length diverges if and when the slow timescale diverges, whatever the microscopic mechanism at the origin of the slowing down. Measuring the length amounts to determining explicitly the complexity from the observed particle configurations. One may compute in the same way the Renyi complexities K_q, their relative behavior for different q characterizes the mechanism underlying the transition. In particular, the 'Random First Order' scenario predicts that in the glass phase K_q=0 for q>x, and K_q>0 for q<x, with x the Parisi parameter. The hypothesis of a nonequilibrium effective temperature may also be directly tested directly from configurations.Comment: Typos corrected, clarifications adde

SUSY Resonances from UHE neutralinos in Neutrino Telescopes and in the Sky

In the Top-down scenarios, the decay of super-heavy particles (m~10^{12-16}GeV), situated in dark-matter halos not very far from our Galaxy, can explain the ultra-high-energy (UHE) cosmic-ray spectrum beyond the Griesen-Zatasepin-Kuzmin cut-off. In the MSSM, a major component of the UHE cosmic-ray flux at PeV-EeV energies could be given by the lightest neutralino \chi, that is the lightest stable supersymmetric particle. Then, the signal of UHE \chi's on earth might emerge over the interactions of a comparable neutrino component. We compute the event rates for the resonant production of "right" selectrons and "right" squarks in mSUGRA, when UHE neutralinos of energy larger than 10^5 GeV scatter off electrons and quarks in an earth-based detector like IceCube. When the resonant channel dominates in the total \chi-e,\chi-q scattering cross section, the only model parameters affecting the corresponding visible signal rates turn out to be the physical masses of the resonant right-scalar and of the lightest neutralino. We compare the expected number of supersymmetric events with the rates corresponding to the expected Glashow W resonance and to the continuum UHE \nu-N scattering for realistic power-law spectra. We find that the event rate in the leptonic selectron channel is particularly promising, and can reach a few tens for a one-year exposure in IceCube. Finally, we note that UHE neutralinos at much higher energies (up to hundreds ZeV) may produce sneutrino resonances by scattering off relic neutrinos in the Local Group hot dark halo. The consequent \tilde{\nu}-burst into hadronic final states could mimic Z-burst events, although with quite smaller conversion efficiency.Comment: 23 pages, 4 figures; one reference adde

Gluon mass generation in the PT-BFM scheme

In this article we study the general structure and special properties of the Schwinger-Dyson equation for the gluon propagator constructed with the pinch technique, together with the question of how to obtain infrared finite solutions, associated with the generation of an effective gluon mass. Exploiting the known all-order correspondence between the pinch technique and the background field method, we demonstrate that, contrary to the standard formulation, the non-perturbative gluon self-energy is transverse order-by-order in the dressed loop expansion, and separately for gluonic and ghost contributions. We next present a comprehensive review of several subtle issues relevant to the search of infrared finite solutions, paying particular attention to the role of the seagull graph in enforcing transversality, the necessity of introducing massless poles in the three-gluon vertex, and the incorporation of the correct renormalization group properties. In addition, we present a method for regulating the seagull-type contributions based on dimensional regularization; its applicability depends crucially on the asymptotic behavior of the solutions in the deep ultraviolet, and in particular on the anomalous dimension of the dynamically generated gluon mass. A linearized version of the truncated Schwinger-Dyson equation is derived, using a vertex that satisfies the required Ward identity and contains massless poles belonging to different Lorentz structures. The resulting integral equation is then solved numerically, the infrared and ultraviolet properties of the obtained solutions are examined in detail, and the allowed range for the effective gluon mass is determined. Various open questions and possible connections with different approaches in the literature are discussed.Comment: 54 pages, 24 figure

Super-Hubble de Sitter Fluctuations and the Dynamical RG

Perturbative corrections to correlation functions for interacting theories in de Sitter spacetime often grow secularly with time, due to the properties of fluctuations on super-Hubble scales. This growth can lead to a breakdown of perturbation theory at late times. We argue that Dynamical Renormalization Group (DRG) techniques provide a convenient framework for interpreting and resumming these secularly growing terms. In the case of a massless scalar field in de Sitter with quartic self-interaction, the resummed result is also less singular in the infrared, in precisely the manner expected if a dynamical mass is generated. We compare this improved infrared behavior with large-N expansions when applicable.Comment: 33 pages, 4 figure

Numerical loop quantum cosmology: an overview

A brief review of various numerical techniques used in loop quantum cosmology and results is presented. These include the way extensive numerical simulations shed insights on the resolution of classical singularities, resulting in the key prediction of the bounce at the Planck scale in different models, and the numerical methods used to analyze the properties of the quantum difference operator and the von Neumann stability issues. Using the quantization of a massless scalar field in an isotropic spacetime as a template, an attempt is made to highlight the complementarity of different methods to gain understanding of the new physics emerging from the quantum theory. Open directions which need to be explored with more refined numerical methods are discussed.Comment: 33 Pages, 4 figures. Invited contribution to appear in Classical and Quantum Gravity special issue on Non-Astrophysical Numerical Relativit

Growth, profits and technological choice: The case of the Lancashire cotton textile industry

Using Lancashire textile industry company case studies and financial records, mainly from the period just before the First World War, the processes of growth and decline are re-examined. These are considered by reference to the nature of Lancashire entrepreneurship and the impact on technological choice. Capital accumulation, associated wealth distributions and the character of Lancashire business organisation were sybiotically linked to the success of the industry before 1914. However, the legacy of that accumulation in later decades, chronic overcapacity, formed a barrier to reconstruction and enhanced the preciptious decline of a once great industry

Phenomenological description of quantum gravity inspired modified classical electrodynamics

We discuss a large class of phenomenological models incorporating quantum gravity motivated corrections to electrodynamics. The framework is that of electrodynamics in a birefringent and dispersive medium with non-local constitutive relations, which are considered up to second order in the inverse of the energy characterizing the quantum gravity scale. The energy-momentum tensor, Green functions and frequency dependent refraction indices are obtained, leading to departures from standard physics. The effective character of the theory is also emphasized by introducing a frequency cutoff. The analysis of its effects upon the standard notion of causality is performed, showing that in the radiation regime the expected corrections get further suppressed by highly oscillating terms, thus forbiding causality violations to show up in the corresponding observational effects.Comment: 14 pages, to be published in Obregon Festschrift 2006, Gen. Rel. and Gra