1,078 research outputs found
Renormalization of high-energy Lorentz-violating QED
No full textWe study a QED extension that is unitary, CPT invariant, and super-renormalizable, but violates Lorentz symmetry at high energies, and contains higher-dimension operators (LVQED). Divergent diagrams are only one- and two-loop. We compute the one-loop renormalizations at high and low energies and analyze the relation between them. It emerges that the powerlike divergences of the low-energy theory are multiplied by arbitrary constants, inherited by the high-energy theory, and therefore can be set to zero at no cost, bypassing the hierarchy problem
Vacuum Cherenkov radiation in quantum electrodynamics with high-energy Lorentz violation
No full textWe study phenomena predicted by a renormalizable, CPT invariant extension of the standard model that contains higher-dimensional operators and violates Lorentz symmetry explicitly at energies greater than some scale Delta(L). In particular, we consider the Cherenkov radiation in vacuo. In a rather general class of dispersion relations, there exists an energy threshold above which radiation is emitted. The threshold is enhanced in composite particles by a sort of kinematic screening mechanism. We study the energy loss and compare the predictions of our model with known experimental bounds on Lorentz violating parameters and observations of ultrahigh-energy cosmic rays. We argue that the scale of Lorentz violation Delta(L) (with preserved CPT invariance) can be smaller than the Planck scale, actually as small as 10(14)-10(15) GeV. Our model also predicts the Cherenkov radiation of neutral particles
“Jeunes filles, vieilles filles. Les contradictions des classes d’âge romaines dans la représentation statuaire.” dans, P. Huon, M. Mauger et V. Huet “La matérialité des rites de passage dans l’Occident romain” 21-22 Septembre 2017, Faculté des lettres et Sciences Humaines Brest.
No full textReal-time continuous acoustic monitoring of marine mammals in the mediterranean sea
No full textThe passive acoustic monitoring of cetaceans is a research method that can provide unique information on the animal’s behaviour since the animals can be studied at great depths and at a long-range without interference. Nevertheless, the real-time data collection, transfer, and analysis using these techniques are difficult to implement and maintain. In this paper, a review of several experiments that have used this approach will be provided. The first class of detectors consists of hydrophone systems housed under buoys on the sea surface with wireless data transmission, while the second type comprises several acoustic detector networks integrated within submarine neutrino telescopes cabled to the shore
Leading and higher twists in the proton polarized structure function g1p at large Bjorken x
No full textA phenomenological parametrization of the proton polarized structure function g1p(x,Q2) is developed for x≳0.02 using deep inelastic data up to ∼50 (GeV/c)2 as well as available experimental results on both photo- and electroproduction of proton resonances. According to the new parametrization the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a zero-crossing point at Q2=0.16±0.04 (GeV/c)2. Then, low-order polarized Nachtmann moments are estimated and their Q2 behavior is investigated in terms of leading and higher twists for Q2≳1 (GeV/c)2. The leading twist is treated at NLO in the strong coupling constant and the effects of higher orders of the perturbative series are estimated using soft-gluon resummation techniques. In the case of the first moment, higher-twist effects are found to be quite small for Q2≳1 (GeV/c)2, and the singlet axial charge has been determined to be a0[10 (GeV/c)2]=0.16±0.09. In the case of higher order moments, which are sensitive to the large-x region, higher-twist effects are significantly reduced by the introduction of soft gluon contributions, but they are still relevant at Q2∼ few (GeV/c)2 at variance with the case of the unpolarized transverse structure function of the proton. Our finding suggests that spin-dependent correlations among partons may have more impact than spin-independent ones. As a by-product, it is also shown that the Bloom-Gilman local duality is strongly violated in the region of polarized electroproduction of the Δ(1232) resonance
Bloom-Gilman duality of inelastic structure functions in nucleon and nuclei
No full textThe Bloom-Gilman local duality of the inelastic structure function of the proton, the deuteron, and light complex nuclei is investigated using available experimental data in the squared four-momentum transfer range from 0.3 to 5 (GeV/c)2. The results of our analysis suggest that the onset of the Bloom-Gilman local duality is anticipated in complex nuclei with respect to the case of the proton and the deuteron. A possible interpretation of this result in terms of a rescaling effect is discussed with particular emphasis on the possibility of reproducing the damping of the nucleon-resonance transitions observed in recent electroproduction data off nuclei
Proton and deuteron radiative capture in light nuclei
No full textDifferential capture View the MathML source and View the MathML source cross sections have been measured at excitation energies between 17 and 41 MeV in 17F and 26 and 39 MeV in 17O at several angles in the 35°–135° interval. The (p, γo) data show, besides a direct capture term, the excitation of giant dipole resonances based on excited states having a probable 2p-1h structure. The main features of the deuteron capture cross section can be understood in terms of a semidirect mechanism with the two nucleons captured in the same single-particle configuration
Proton and deuteron radiative capture to A = 13 nuclei
No full textDifferential capture 12C(p, γ)13N and 11B(d, γ)13C cross sections have been measured in the excitation energy region between 20 and 45 MeV in 13N and 25 and 42 MeV in 13C. Angular distributions are given for the pγ channel at each energy, while the dγ excitation function has been measured at 60°. The pγ0 data show, besides a direct capture term, the excitation of giant dipole resonances based on excited states of the compound nucleus. The main feature of the deuteron capture cross section can be understood in terms of a mechanism in which the proton-neutron pair is captured in the same single particle configuration by the 11B core
- …
