References of "Cudell, Jean-René"
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See detailA new analysis of quasar polarization alignments
Pelgrims, Vincent ULg; Cudell, Jean-René ULg

in Monthly Notices of the Royal Astronomical Society (2014), 442(1), 1239-1248

We propose a new method to analyse the alignment of optical polarization vectors from quasars. This method leads to a definition of intrinsic preferred axes and to a determination of the probability that ... [more ▼]

We propose a new method to analyse the alignment of optical polarization vectors from quasars. This method leads to a definition of intrinsic preferred axes and to a determination of the probability that the distribution of polarization directions is random. This probability is found to be as low as 0,003 percent for one of the region of redshift. [less ▲]

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See detailDark Atoms and Dark Radiation
Khlopov, Maxim; Belotsky, Konstantin; Cudell, Jean-René ULg et al

Book published by Hindawi Publishing Corporation (2014)

We have invited investigators to contribute original research and review articles that seek to define the possible physical nature of composite dark matter and its constituents, to stimulate the ... [more ▼]

We have invited investigators to contribute original research and review articles that seek to define the possible physical nature of composite dark matter and its constituents, to stimulate the experimental searches and to suggest astrophysical tests for their effects. The collected papers in this special issue represent only a first small step in the approach to the thorough investigation of the topic of dark atoms and dark radiation, demonstrating the wide but far from complete variety of possible aspects of this problem. [less ▲]

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See detailDark atoms and the positron-annihilation-line excess in the galactic bulge
Cudell, Jean-René ULg; Khlopov, Maxim; Wallemacq, Quentin ULg

in Advances in High Energy Physics (2014), 2014

It was recently proposed that stable particles of charge -2, O^{--}, can exist and constitute dark matter after they bind with primordial helium in O-helium (OHe) atoms. We study here in details the ... [more ▼]

It was recently proposed that stable particles of charge -2, O^{--}, can exist and constitute dark matter after they bind with primordial helium in O-helium (OHe) atoms. We study here in details the possibility that this model provides an explanation for the excess of gamma radiation in the positron-annihilation line from the galactic bulge observed by INTEGRAL. This explanation assumes that OHe, excited to a 2s state through collisions in the central part of the Galaxy, de-excites to its ground state via an E0 transition, emitting an electron-positron pair. The cross section for OHe collisions with excitation to 2s level is calculated and it is shown that the rate of such excitations in the galactic bulge strongly depends not only on the mass of O-helium, which is determined by the mass of O^{--}, but also on the density and velocity distribution of dark matter. Given the astrophysical uncertainties on these distributions, this mechanism constrains the O^{--} mass to lie in two possible regions. One of these is reachable in the experimental searches for stable multicharged particles at the LHC. [less ▲]

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See detailThe nuclear physics of OHe
Cudell, Jean-René ULg; Khlopov, Maxim; Wallemacq, Quentin ULg

in Mankoc (Ed.) Proceedings of the 15th Bled Workshop "What Comes Beyond the Standard Models" (2012, November 24)

A recent composite-dark-matter scenario assumes that the dominant fraction of dark matter consists of O-helium (OHe) dark atoms, in which a lepton-like doubly charged particle O is bound with a primordial ... [more ▼]

A recent composite-dark-matter scenario assumes that the dominant fraction of dark matter consists of O-helium (OHe) dark atoms, in which a lepton-like doubly charged particle O is bound with a primordial helium nucleus. It liberates the physics of dark matter from unknown features of new physics, but it demands a deep understanding of the details of known nuclear and atomic physics, which are still unclear. Here, we consider in detail the physics of the binding of OHe to various nuclei of interest for direct dark matter searches. We show that standard quantum mechanics leads to bound states in the keV region, but does not seem to provide a simple mechanism that stabilizes them. The crucial role of a barrier in the OHe-nucleus potential is confirmed for such a stabilization. [less ▲]

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See detailNew polarimetric constraints on axion-like particles
Payez, Alexandre ULg; Cudell, Jean-René ULg; Hutsemekers, Damien ULg

in Journal of Cosmology and Astroparticle Physics [= JCAP] (2012), 1207

We show that the parameter space of axion-like particles can be severly constrained using high-precision measurements of quasar polarisations. Robust limits are derived from the measured bounds on optical ... [more ▼]

We show that the parameter space of axion-like particles can be severly constrained using high-precision measurements of quasar polarisations. Robust limits are derived from the measured bounds on optical circular polarisation and from the distribution of linear polarisations of quasars. As an outlook, this technique can be improved by the observation of objects located behind clusters of galaxies, using upcoming space-borne X-ray polarimeters. [less ▲]

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See detailNew constraints on very light pseudoscalars
Payez, Alexandre ULg; Cudell, Jean-René ULg; Hutsemekers, Damien ULg

in Zioutas, K. (Ed.) 7th Patras Workshop on Axions, WIMPs and WISPs (2012, January 01)

Nearly massless axion-like particles are of interest for astrophysical observations, and some constraints on their parameter space do exist in the literature. Here, we propose to put new constraints on ... [more ▼]

Nearly massless axion-like particles are of interest for astrophysical observations, and some constraints on their parameter space do exist in the literature. Here, we propose to put new constraints on these particles using polarisation and, in particular, the polarisation differences observed between different quasar classes. [less ▲]

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See detailDispersion relations for meson-proton and proton-proton forward elastic scattering
Alkin, A.; Cudell, Jean-René ULg; Martynov, E.

in Cudell, Jean-René; Lansberg, Jean-Philippe; Mancusi, Davide (Eds.) 30 Years of Strong Interactions: a Three-Day Meeting in Honour of Joseph Cugnon and Hans-Jürgen Pirner (2012)

An analysis of the data on forward $pp, \bar pp, \pi^{\pm}p$ and $K^{\pm}p$ scattering is performed making use of the single- and double-subtraction integral and comparing with derivative dispersion ... [more ▼]

An analysis of the data on forward $pp, \bar pp, \pi^{\pm}p$ and $K^{\pm}p$ scattering is performed making use of the single- and double-subtraction integral and comparing with derivative dispersion relations for amplitudes. Various pomeron and odderon models for the total cross sections are considered and compared. The real part of the amplitude is calculated via dispersion relations. It is shown that the integral dispersion relations lead to a better description of the data for $\sqrt{s}>$5 GeV. Predictions of the considered models for the TOTEM experiment at LHC energies are given [less ▲]

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See detailHiggs Central Exclusive Production
Cudell, Jean-René ULg; Dechambre, Alice; Henandez, Oscar F.

in Physics Letters B (2012), 706

We tune the calculation of central exclusive Higgs production to the recent CDF central exclusive dijet data, and predict the cross section for the exclusive production of Higgs boson at the LHC. It is ... [more ▼]

We tune the calculation of central exclusive Higgs production to the recent CDF central exclusive dijet data, and predict the cross section for the exclusive production of Higgs boson at the LHC. It is always below 1 fb, and below 0.3 fb after experimental cuts. [less ▲]

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See detailLarge-Scale Alignments of Quasar Polarization Vectors: Evidence at Cosmological Scales for Very Light Pseudoscalar Particles Mixing with Photons ?
Hutsemekers, Damien ULg; Payez, Alexandre ULg; Cabanac, R et al

in Bastien, Pierre (Ed.) Astronomical Polarimetry 2008: Science from Small to Large Telescopes. ASPC 449 (2011, November 01)

Based on a sample of 355 quasars with significant optical polarization, we found that quasar polarization vectors are not randomly oriented over the sky as naturally expected. The probability that the ... [more ▼]

Based on a sample of 355 quasars with significant optical polarization, we found that quasar polarization vectors are not randomly oriented over the sky as naturally expected. The probability that the observed distribution of polarization angles is due to chance is lower than 0.1%. The polarization vectors of the light from quasars are aligned although the sources span huge regions of the sky (˜ 1 Gpc). Groups of quasars located along similar lines of sight but at different redshifts (typically z ≍ 0.5 and z ≍ 1.5) are characterized by different preferred directions of polarization. These characteristics make the observed alignment effect difficult to explain in terms of a local contamination by interstellar polarization in our Galaxy. Interpreted in terms of a cosmological-size effect, we show that the dichroism and birefringence predicted by a mixing between photons and very light pseudoscalar particles within a magnetic field can qualitatively reproduce the observations. We find that circular polarization measurements could help constrain this mechanism. [less ▲]

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See detailCan axionlike particles explain the alignments of the polarizations of light from quasars?
Payez, Alexandre ULg; Cudell, Jean-René ULg; Hutsemekers, Damien ULg

in Physical Review. D : Particles and Fields (2011), 84

The standard axion-like particle explanation of the observed large-scale coherent orientations of quasar polarisation vectors is ruled out by the recent measurements of vanishing of circular polarisation ... [more ▼]

The standard axion-like particle explanation of the observed large-scale coherent orientations of quasar polarisation vectors is ruled out by the recent measurements of vanishing of circular polarisation. We introduce a more general wave-packet formalism and show that, although decoherence effects between waves of different frequencies can reduce significantly the amount of circular polarisation, the axion-like particle hypothesis is disfavoured given the bandwidth with which part of the observations were performed. Finally, we show that a more sophisticated model of extragalactic fields does not lead to an alignment of polarisations. [less ▲]

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See detailchi-gamma mixing in an expanding universe
Mandal, Subhayan ULg; Cudell, Jean-René ULg

in PoS - Proceedings of Science (2011, August)

We establish the equation of motion of pseudoscalar particles coupled to an electro- magnetic field in a classical gravitational background through the use of conformal time and flat geometry. We show ... [more ▼]

We establish the equation of motion of pseudoscalar particles coupled to an electro- magnetic field in a classical gravitational background through the use of conformal time and flat geometry. We show that the expansion of the universe can lead to larger mixing than in a station- ary universe. We also show that for a broad range of parameters, one can obtain resonant mixing, i.e. a region in which the mixing becomes maximum. [less ▲]

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See detailThe slope of the hadron spin-flip amplitude and the determination of \rho(s,t)
Selyugin, O. V.; Cudell, Jean-René ULg; Predazzi, E.

in A.V. Efremov, A.V.; Goloskokov, S.V. (Eds.) DSPIN-11, proceedings (2011)

We re-examine the extraction of \rho(s,t), the ratio of the real part to the imaginary part of the scattering amplitude, and of the spin-flip amplitude, from the existing experimental data in the Coulomb ... [more ▼]

We re-examine the extraction of \rho(s,t), the ratio of the real part to the imaginary part of the scattering amplitude, and of the spin-flip amplitude, from the existing experimental data in the Coulomb-hadron interference region. We show that it is not possible to find reasonable assumptions about the structure of the scattering amplitude of proton-proton and proton-antiproton elastic scattering at high energy that would lead, in proton-antiproton scattering for 3.8 < p_L <6 GeV/c, to an agreement between data and an analysis based on dispersion relations. [less ▲]

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See detailLarge-scale coherent orientations of quasar polarisation vectors: interpretation in terms of axion-like particles
Payez, Alexandre ULg; Hutsemekers, Damien ULg; Cudell, Jean-René ULg

in AIP Conference Proceedings (2010), 1274,

The observation of redshift-dependent coherent orientations of quasar polarisation vectors over cosmological distances in some regions of the sky is reviewed. Based on a good-quality sample of 355 ... [more ▼]

The observation of redshift-dependent coherent orientations of quasar polarisation vectors over cosmological distances in some regions of the sky is reviewed. Based on a good-quality sample of 355 measured quasars, this observation seems to infer the existence of a new effect acting on light propagation on such huge distances. A solution in terms of nearly massless axion-like particles has been proposed in the literature and its current status is discussed. [less ▲]

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See detailAsymptotics of the S-matrix and unitarisation
Selyugin, O. V.; Cudell, Jean-René ULg

in Physics of Particles and Nuclei (2010), 41

The manner in which the elastic scattering amplitude obeys unitarity, how it enters the circle of unitarity, and what its asymptotic limit is, remains a problem for models which include terms that rise ... [more ▼]

The manner in which the elastic scattering amplitude obeys unitarity, how it enters the circle of unitarity, and what its asymptotic limit is, remains a problem for models which include terms that rise fast with s. We have checked that the features of cross sections which come from unitarisation are present for most unitarisation schemes, e.g. those that saturate the profile function or those that describe multiple exchanges via an analytic formula. We have also obtained a scheme which interpolates between different classes of the unitarisation and found corresponding non-linear equations. Considering different forms of energy dependence of the scattering amplitude, and a variety of unitarisation schemes, we show that, in order to reproduce the data, the fits choose an amplitude that corresponds to an asymptotic value S = 0. [less ▲]

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See detailLong-range potential and the fine structure of the diffraction peak
Selyugin, O. V.; Cudell, Jean-René ULg

in Capua, Marcella (Ed.) DIFFRACTION 2010: International Workshop on Diffraction in High Energy Physics Diffraction in High Energy Physics (2010)

The possibility of oscillations in the differential elastic cross section of hadron scattering at small momentum transfer is studied. It is shown that string-like quark potentials at large distances can ... [more ▼]

The possibility of oscillations in the differential elastic cross section of hadron scattering at small momentum transfer is studied. It is shown that string-like quark potentials at large distances can lead to such small oscillations, and an analysis of the experimental data at small |t| allows the determination of the parameters of the potential. [less ▲]

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See detailCentral exclusive production: Vector mesons, dijets, Higgs boson
Cudell, Jean-René ULg

(2010)

I review the situation of theoretical predictions of central exclusive production, and show that the CDF dijet data can be used to constrain the prediction of central exclusive Higgs boson production. I ... [more ▼]

I review the situation of theoretical predictions of central exclusive production, and show that the CDF dijet data can be used to constrain the prediction of central exclusive Higgs boson production. I also show that central exclusive production might be used as a discovery tool for the odderon. [less ▲]

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See detailThe Total Cross Section at the LHC: Models and Experimental Consequences
Cudell, Jean-René ULg

(2010)

I review the predictions of the total cross section for many models, and point out that some of them lead to the conclusion that the standard experimental analysis may lead to systematic errors much ... [more ▼]

I review the predictions of the total cross section for many models, and point out that some of them lead to the conclusion that the standard experimental analysis may lead to systematic errors much larger than expected. [less ▲]

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See detailOn the circular polarisation of light from axion-photon mixing
Payez, Alexandre ULg; Cudell, Jean-René ULg; Hutsemekers, Damien ULg

in Alimi, Jean-Michel; Füzfa, André (Eds.) INVISIBLE UNIVERSE: Proceedings of the Conference. AIP Conference Proceedings 1241. (2010)

From the analysis of measurements of the linear polarisation of visible light coming from quasars, the existence of large-scale coherent orientations of quasar polarisation vectors in some regions of the ... [more ▼]

From the analysis of measurements of the linear polarisation of visible light coming from quasars, the existence of large-scale coherent orientations of quasar polarisation vectors in some regions of the sky has been reported. Here, we show that this can be explained by the mixing of the incoming photons with nearly massless pseudoscalar (axion-like) particles in extragalactic magnetic fields. We present a new treatment in terms of wave packets and discuss its implications for the circular polarisation. [less ▲]

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See detailAxion-like particles and circular polarisation of active galactic nuclei
Payez, Alexandre ULg; Cudell, Jean-René ULg; Hutsemekers, Damien ULg

in Jaeckel, Joerg; Lindner, Axel; Redondo, Javier (Eds.) Proceedings of the 5th Patras Workshop on Axions, WIMPs and WISPs PATRAS 2009 (2010)

The measurements of the linear polarisation of visible light from quasars give strong evidence for large-scale coherent orientations of their polarisation vectors in some regions of the sky. We show that ... [more ▼]

The measurements of the linear polarisation of visible light from quasars give strong evidence for large-scale coherent orientations of their polarisation vectors in some regions of the sky. We show that these observations can be explained by the mixing of the photons with very light pseudoscalar (axion-like) particles in extragalactic magnetic fields during their propagation. We present a new treatment in terms of wave packets and discuss the circular polarisation. [less ▲]

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