39,399 research outputs found

    The spectrum of massive excitations of 3d 3-state Potts model and universality

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    We consider the mass spectrum of the 3dd 3-state Potts model in the broken phase (a) near the second order Ising critical point in the temperature - magnetic field plane and (b) near the weakly first order transition point at zero magnetic field. In the case (a), we compare the mass spectrum with the prediction from universality of mass ratios in the 3dd Ising class; in the case (b), we determine a mass ratio to be compared with the corresponding one in the spectrum of screening masses of the (3+1)dd SU(3) pure gauge theory at finite temperature in the deconfined phase near the transition. The agreement in the comparison in the case (a) would represent a non-trivial test of validity of the conjecture of spectrum universality. A positive answer to the comparison in the case (b) would suggest the possibility to extend this conjecture to weakly first order phase transitions.Comment: 20 pages, 12 figures; uses axodraw.st

    New results on semileptonic b decays from LHCb

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    We report new measurements, based on the Run I dataset collected by the LHCb experiment, of the B0 mixing frequency Dm_d and the CKM matrix element |V_ub| using semileptonic b decays. The former is the most precise measurement ever performed; the latter represents the first determination of |V_ub| using a baryonic decay, and adds an important constraint on a possible explanation for the discrepancy between exclusive and inclusive determinations of this observable.Comment: Presentation at the DPF 2015 Meeting of the American Physical Society Division of Particles and Fields, Ann Arbor, Michigan, August 4-8, 201

    On very short and intense laser-plasma interactions

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    We briefly report on some results regarding the impact of very short and intense laser pulses on a cold, low-density plasma initially at rest, and the consequent acceleration of plasma electrons to relativistic energies. Locally and for short times the pulse can be described by a transverse plane electromagnetic travelling-wave and the motion of the electrons by a purely Magneto-Fluido-Dynamical (MFD) model with a very simple dependence on the transverse electromagnetic potential, while the ions can be regarded as at rest; the Lorentz-Maxwell and continuity equations are reduced to the Hamilton equations of a Hamiltonian system with 1 degree of freedom, in the case of a plasma with constant initial density, or a collection of such systems otherwise. We can thus describe both the well-known "wakefield" behind the pulse and the recently predicted "slingshot effect", i.e. the backward expulsion of high energy electrons just after the laser pulse has hit the surface of the plasma.Comment: Latex file, 15 pages, 6 figure

    The q-Euclidean algebra Uq(eN)U_q(e^N) and the corresponding q-Euclidean lattice

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    We review the Euclidean Hopf algebra Uq(eN)U_q(e^N) dual of Fun(\rn_q^N\lcross SO_{q^{-1}}(N)) and describe its fundamental Hilbert space representations \cite{fioeu}, which turn out to be rather simple "lattice-regularized" versions of the classical ones, in the sense that the spectra of squared momentum components are discrete and the corresponding eigenfunctions normalizable.These representations can be regarded as describing a quantum system consisting of one free particle on the quantum Euclidean space. A suitable notion of classical limit is introduced, so that we recover the classical continuous spectra and generalized (non-normalizable) eigenfunctions in that limit.Comment: 19pages, latex. transmission error correcte

    Travelling waves and a fruitful `time' reparametrization in relativistic electrodynamics

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    We simplify the nonlinear equations of motion of charged particles in an external electromagnetic field that is the sum of a plane travelling wave F_t(ct-z) and a static part F_s(x,y,z): by adopting the light-like coordinate ct-z instead of time t as an independent variable in the Action, Lagrangian and Hamiltonian, and deriving the new Euler-Lagrange and Hamilton equations accordingly, we make the unknown z(t) disappear from the argument of F_t. We study and solve first the single particle equations in few significant cases of extreme accelerations. In particular we obtain a rigorous formulation of a Lawson-Woodward-type (no-final-acceleration) theorem and a compact derivation of cyclotron autoresonance, beside new solutions in the presence of uniform F_s. We then extend our method to plasmas in hydrodynamic conditions and apply it to plane problems: the system of partial differential equations may be partially solved and sometimes even completely reduced to a family of decoupled systems of ordinary ones; this occurs e.g. with the impact of the travelling wave on a vacuum-plasma interface (what may produce the slingshot effect). Since Fourier analysis plays no role in our general framework, the method can be applied to all kind of travelling waves, ranging from almost monochromatic to socalled "impulses", which contain few, one or even no complete cycle.Comment: Latex file, 35 pages, 6 figures. Final version to appear in J. Phys. A: Math. Theo

    Noncommutative spaces with twisted symmetries and second quantization

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    In a minimalistic view, the use of noncommutative coordinates can be seen just as a way to better express non-local interactions of a special kind: 1-particle solutions (wavefunctions) of the equation of motion in the presence of an external field may look simpler as functions of noncommutative coordinates. It turns out that also the wave-mechanical description of a system of n such bosons/fermions and its second quantization is simplified if we translate them in terms of their deformed counterparts. The latter are obtained by a general twist-induced *-deformation procedure which deforms in a coordinated way not just the spacetime algebra, but the larger algebra generated by any number n of copies of the spacetime coordinates and by the particle creation and annihilation operators. On the deformed algebra the action of the original spacetime transformations looks twisted. In a non-conservative view, we thus obtain a twisted covariant framework for QFT on the corresponding noncommutative spacetime consistent with quantum mechanical axioms and Bose-Fermi statistics. One distinguishing feature is that the field commutation relations remain of the type "field (anti)commutator=a distribution". We illustrate the results by choosing as examples interacting non-relativistic and free relativistic QFT on Moyal space(time)s.Comment: Latex file 16 pages. Talk given at the conference "Noncommutative Structures in Mathematics and Physics" (Satellite Conference to the 5th European Congress of Mathematics), Brussels 22-26/7/2008. Appeared in the Proceedings, Ed. S. Caenepeel, J. Fuchs, S. Gutt, C. Schweigert, A. Stolin, F. Van Oystaeyen, Royal Flemish Academy of Belgium for Sciences and Arts, brussels, 2010, pp. 163-17

    Multiwavelength perspective of AGN evolution

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    Discovering and studying obscured AGN at z>1-3 is important not only to complete the AGN census, but also because they can pinpoint galaxies where nuclear accretion and star-formation are coeval, and mark the onset of AGN feedback. We present the latest results on the characterization of z=1-3 galaxies selected for their high mid-infrared to optical flux ratio, showing that they are massive and strongly star-forming galaxies, and that many do host highly obscured AGN. We present a pilot program to push the search of moderately obscured AGN up to z=5-6 and discuss the perspectives of this line of research.Comment: Invited talk at the conference: X-Ray Astronomy 2009, Present Status, multiwavelength approach and future perspectives, September 2009, Bologn

    On the consequences of twisted Poincare' symmetry upon QFT on Moyal noncommutative spaces

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    We explore some general consequences of a consistent formulation of relativistic quantum field theory (QFT) on the Groenewold-Moyal-Weyl noncommutative versions of Minkowski space with covariance under the twisted Poincare' group of Chaichian et al. [12], Wess [44], Koch et al. [31], Oeckl [34]. We argue that a proper enforcement of the latter requires braided commutation relations between any pair of coordinates x^,y^\hat x,\hat y generating two different copies of the space, or equivalently a ⋆\star-tensor product f(x)⋆g(y)f(x)\star g(y) (in the parlance of Aschieri et al. [3]) between any two functions depending on x,yx,y. Then all differences (x−y)μ(x-y)^\mu behave like their undeformed counterparts. Imposing (minimally adapted) Wightman axioms one finds that the nn-point functions fulfill the same general properties as on commutative space. Actually, upon computation one finds (at least for scalar fields) that the nn-point functions remain unchanged as functions of the coordinates' differences both if fields are free and if they interact (we treat interactions via time-ordered perturbation theory). The main, surprising outcome seems a QFT physically equivalent to the undeformed counterpart (to confirm it or not one should however first clarify the relation between nn-point functions and observables, in particular S-matrix elements). These results are mainly based on a joint work [24] with J. WessComment: Latex file, 21 page

    Embedding q-deformed Heisenberg Algebras into Undeformed Ones

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    Any deformation of a Weyl or Clifford algebra can be realized through some change of generators in the undeformed algebra. Here we briefly describe and motivate our systematic procedure for constructing all such changes of generators for those particular deformations where the original algebra is covariant undersome Lie group and the deformed algebra is covariant under the corresponding quantum group.Comment: LaTex2e file, 8 pages, no figure. To appear in Rep. Math Phy

    Radiation damage effects on detectors and eletronic devices in harsh radiation environment

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    Radiation damage effects represent one of the limits for technologies to be used in harsh radiation environments as space, radiotherapy treatment, high-energy phisics colliders. Different technologies have known tolerances to different radiation fields and should be taken into account to avoid unexpected failures which may lead to unrecoverable damages to scientific missions or patient health
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