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See detailExplaining the CMS Higgs lepton-flavor violating
Aristizabal Sierra, Diego ULg; Vicente, Avelino ULg

in Physical Review. D : Particles and Fields (2014), 90(11), 115004

Direct searches for lepton flavor violating Higgs boson decays in the τ μ channel have been recently reported by the CMS collaboration. The results display a slight excess of signal events with a ... [more ▼]

Direct searches for lepton flavor violating Higgs boson decays in the τ μ channel have been recently reported by the CMS collaboration. The results display a slight excess of signal events with a significance of 2.5σ, which translates into a branching ratio of about 1%. By interpreting these findings as a hint for beyond the standard model physics, we show that the Type-III 2HDM is capable of reproducing such signal while at the same time satisfying vacuum stability, perturbativity, electroweak precision data, measured Higgs standard decay modes and low-energy lepton flavor violating constraints. We have found that the allowed signal strength ranges for the bb, WW* and ZZ* standard channels shrink as soon as BR(h→τμ)∼ 1% is enforced. Thus, we point out that if the excess persists, improved measurements of these channels may be used to test our Type-III 2HDM scenario. [less ▲]

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See detail[70,l+] baryons in large Nc QCD revisited: The effect on Regge trajectories
Matagne, Nicolas; Stancu, Floarea ULg

in Physical Review. D : Particles and Fields (2013), 87(April), 076012

A simple procedure within the 1/N_c expansion method where all the N_c quarks are treated on the same footing has been found successful in describing mixed symmetric negative parity baryon states ... [more ▼]

A simple procedure within the 1/N_c expansion method where all the N_c quarks are treated on the same footing has been found successful in describing mixed symmetric negative parity baryon states belonging to the [{\bf 70},\ell^-] multiplets of the N = 1 and 3 bands. Presently it is applied to mixed symmetric positive parity [{\bf 70},0^+] and [{\bf 70},2^+] multiplets of the N = 2 band. We search for the most dominant terms in the mass formula. The results are compared to those obtained in the procedure where the system is separated into a core and an excited quark. We find that both the spin and isospin operators of the entire system of N_c quarks play dominant roles in describing the data, like for negative parity states. As a by-product we present the contribution of the leading spin-isospin singlet term as a function of the band number, which hints at distinct Regge trajectories for the symmetric and mixed symmetric states. [less ▲]

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See detailAccessing baryon to meson transition distribution amplitudes in meson production in association with a high invariant mass lepton pair at GSI-FAIR with P̅ ANDA
Lansberg, Jean-Philippe ULg; Pire, Bernard; Semenov-Tyan-Shanskiy, Kirill ULg et al

in Physical Review. D : Particles and Fields (2012), 86

Nucleon-antinucleon annihilation into a near backward- (or forward-) produced meson and a high invariant mass lepton pair admits a factorized description in terms of antinucleon (or nucleon) distribution ... [more ▼]

Nucleon-antinucleon annihilation into a near backward- (or forward-) produced meson and a high invariant mass lepton pair admits a factorized description in terms of antinucleon (or nucleon) distribution amplitudes (DAs) and nucleon to meson (or antinucleon to meson) transition distribution amplitudes (TDAs). We estimate the cross section of backward (and forward) pion and eta-meson production in association with a high invariant mass lepton pair for the kinematical conditions of GSI-FAIR. The cross sections are found to be large enough to be measured with the PANDA detector. Interesting phenomenological applications of the approach are thus expected. [less ▲]

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See detailDiscrete symmetries in the three-Higgs-doublet model
Ivanov, Igor ULg; Vdovin, Evgeny

in Physical Review. D : Particles and Fields (2012), 86(9), 0950305

N-Higgs-doublet models (NHDM) are among the most popular examples of electroweak symmetry breaking mechanisms beyond the Standard Model. Discrete symmetries imposed on the NHDM scalar potential play a ... [more ▼]

N-Higgs-doublet models (NHDM) are among the most popular examples of electroweak symmetry breaking mechanisms beyond the Standard Model. Discrete symmetries imposed on the NHDM scalar potential play a pivotal role in shaping the phenomenology of the model, and various symmetry groups have been studied so far. However, in spite of all efforts, the classification of finite Higgs-family symmetry groups realizable in NHDM for any N>2 is still missing. Here, we solve this problem for the three-Higgs-doublet model by making use of Burnside’s theorem and other results from pure finite group theory which are rarely exploited in physics. Our method and results can also be used beyond high-energy physics, for example, in the study of possible symmetries in three-band superconductors. [less ▲]

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See detailNegative parity baryons in the 1/Nc expansion: the three towers of states revisited.
Matagne, Nicolas; Stancu, Floarea ULg

in Physical Review. D : Particles and Fields (2012), D86

We discuss the compatibility between the quark-shell picture and the meson-nucleon scattering picture in large $N_c$ QCD for mixed symmetric $\ell$ = 1 states previously analyzed by using a simple ... [more ▼]

We discuss the compatibility between the quark-shell picture and the meson-nucleon scattering picture in large $N_c$ QCD for mixed symmetric $\ell$ = 1 states previously analyzed by using a simple Hamiltonian including operators up to order $\mathcal{O}(N^0_c)$ defined in the standard ground state symmetric core + excited quark procedure. Here we introduce a Hamiltonian of order $\mathcal{O}(N^0_c)$ defined in a new approach where the separation of the system into two parts is not required. Three degenerate sets of states (towers) with the same quantum numbers as in the scattering picture and in the standard procedure are obtained. Thus the compatibility is equally achieved. The eigenvalues of the presently chosen Hamiltonian also have simple analytic expressions, depending linearly on the three dynamical coefficients entering the Hamiltonian. This reinforces the validity of the new approach which had already successfully described excited negative parity baryons in a large energy range. [less ▲]

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See detailZ_p scalar dark matter from multi-Higgs-doublet models
Ivanov, Igor ULg; Keus, Venus ULg

in Physical Review. D : Particles and Fields (2012), 86(1), 0160047

In many models, stability of dark matter particles is protected by a conserved Z_2 quantum number. However dark matter can be stabilized by other discrete symmetry groups, and examples of such models with ... [more ▼]

In many models, stability of dark matter particles is protected by a conserved Z_2 quantum number. However dark matter can be stabilized by other discrete symmetry groups, and examples of such models with custom-tailored field content have been proposed. Here we show that electroweak symmetry breaking models with N Higgs doublets can readily accommodate scalar dark matter candidates stabilized by groups Z_p with any $p \le 2^{N-1}$, leading to a variety of kinds of microscopic dynamics in the dark sector. We give examples in which semi-annihilation or multiple semi-annihilation processes are allowed or forbidden, which can be especially interesting in the case of asymmetric dark matter. [less ▲]

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See detailHighly excited negative parity baryons in the 1/Nc expansion.
Matagne, Nicolas ULg; Stancu, Floarea ULg

in Physical Review. D : Particles and Fields (2012), D85

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See detailCornering the axionlike particle explanation of quasar polarizations
Payez, Alexandre ULg

in Physical Review. D : Particles and Fields (2012), 85(8), 087701

In a series of papers, it has been shown that the distribution of polarization position angles for visible light from quasars is not random in extremely large regions of the sky. As explained in a recent ... [more ▼]

In a series of papers, it has been shown that the distribution of polarization position angles for visible light from quasars is not random in extremely large regions of the sky. As explained in a recent article, the measurement of vanishing circular polarization for such quasars is an important problem for a mechanism involving the mixing with axionlike particles in external magnetic fields. In this paper, we stress that a recent report of similar coherent orientations of polarization in radio waves further disfavors the need for such particles, as an effect at these wavelengths would be extremely suppressed or would directly contradict data. [less ▲]

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See detailMeasuring the phase of the scattering amplitude with vortex beams
Ivanov, Igor ULg

in Physical Review. D : Particles and Fields (2012), 85(7), 07600110

We show that colliding vortex beams instead of (approximate) plane waves can lead to a direct measurement of how the overall phase of the plane wave scattering amplitude changes with the scattering angle ... [more ▼]

We show that colliding vortex beams instead of (approximate) plane waves can lead to a direct measurement of how the overall phase of the plane wave scattering amplitude changes with the scattering angle. Since vortex beams are coherent superpositions of plane waves with different momenta, their scattering amplitude receives contributions from plane wave amplitudes with distinct kinematics. These contributions interfere, leading to the measurement of their phase difference. Although interference exists for any generic wave packet collision, we show that using vortex beams dramatically enhances sensitivity to the phase in comparison with nonvortex beams. Since the overall phase is inaccessible in a plane wave collision, this measurement would be of great importance for a number of topics in hadronic physics, for example, meson production in the resonance region, physics of nucleon resonances, and small angle elastic hadron scattering. [less ▲]

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See detailConsistent model for \pi N transition distribution amplitudes and backward pion electroproduction
Lansberg, Jean-Philippe ULg; Pire, Bernard; Semenov-Tian-Chanski, Kirill ULg et al

in Physical Review. D : Particles and Fields (2012), 85

The extension of the concept of generalized parton distributions leads to the introduction of baryon to meson transition distribution amplitudes (TDAs), nondiagonal matrix elements of the nonlocal three ... [more ▼]

The extension of the concept of generalized parton distributions leads to the introduction of baryon to meson transition distribution amplitudes (TDAs), nondiagonal matrix elements of the nonlocal three quark operator between a nucleon and a meson state. We present a general framework for modeling nucleon to pion (\pi N) TDAs. Our main tool is the spectral representation for \pi N TDAs in terms of quadruple distributions. We propose a factorized Ansatz for quadruple distributions with input from the soft-pion theorem for \pi N TDAs. The spectral representation is complemented with a D-term like contribution from the nucleon exchange in the cross channel. We then study backward pion electroproduction in the QCD collinear factorization approach in which the nonperturbative part of the amplitude involves N TDAs. Within our two component model for N TDAs, we update previous leading-twist estimates of the unpolarized cross section. Finally, we compute the transverse target single spin asymmetry as a function of skewness. We find it to be sizable in the valence region and sensitive to the phenomenological input of our \pi N TDA model. [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 detailColliding particles carrying nonzero orbital angular momentum
Ivanov, Igor ULg

in Physical Review. D : Particles and Fields (2011), 83(9), 093001

Photons carrying nonzero orbital angular momentum (twisted photons) are well-known in optics. Recently, using Compton backscattering to boost optical twisted photons to high energies was suggested ... [more ▼]

Photons carrying nonzero orbital angular momentum (twisted photons) are well-known in optics. Recently, using Compton backscattering to boost optical twisted photons to high energies was suggested. Twisted electrons in the intermediate energy range have also been produced recently. Thus, collisions involving energetic twisted particles seem to be feasible and represent a new tool in high-energy physics. Here we discuss some generic features of scattering processes involving twisted particles in the initial and/or final state. In order to avoid additional complications arising from nontrivial polarization states, we focus here on scalar fields only. We show that processes involving twisted particles allow one to perform a Fourier analysis of the plane-wave cross section with respect to the azimuthal angles of the initial particles. In addition, using twisted states, one can probe the autocorrelation function of the amplitude, which is inaccessible in the plane-wave collisions. Finally, we discuss prospects for experimental study of these effects. [less ▲]

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See detailSU(6) [70,1-] baryon multiplet in the 1/N_c expansion
Matagne, Nicolas; Stancu, Floarea ULg

in Physical Review. D : Particles and Fields (2011), 83

The masses of excited states of mixed orbital symmetry of nonstrange and strange baryons belonging to the lowest $[{\bf 70},1^-]$ multiplet are calculated in the $1/N_c$ expansion to order $1/N_c$ with a ... [more ▼]

The masses of excited states of mixed orbital symmetry of nonstrange and strange baryons belonging to the lowest $[{\bf 70},1^-]$ multiplet are calculated in the $1/N_c$ expansion to order $1/N_c$ with a new method which allows to considerably reduce the number of linearly independent operators entering the mass formula. This study represents an extension to SU(6) of our work on nonstrange baryons, the framework of which was SU(4). The conclusion regarding the role of the flavor operator, neglected in previous SU(6) studies, is reinforced. Namely, both the flavor and spin operators contribute dominantly to the flavor-spin breaking. [less ▲]

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See detailUncertainties on exclusive diffractive Higgs boson and jet production at the LHC
Dechambre, Alice ULg; Kepka, Oldrich; Royon, Christophe et al

in Physical Review. D : Particles and Fields (2011), D83

Two theoretical descriptions of exclusive diffractive jets and Higgs production at the LHC were implemented into the FPMC generator: the Khoze, Martin, Ryskin model and the Cudell, Hern\'andez, Ivanov ... [more ▼]

Two theoretical descriptions of exclusive diffractive jets and Higgs production at the LHC were implemented into the FPMC generator: the Khoze, Martin, Ryskin model and the Cudell, Hern\'andez, Ivanov, Dechambre exclusive model. We then study the uncertainties. We compare their predictions to the CDF measurement and discuss the possibility of constraining the exclusive Higgs production at the LHC with early measurements of exclusive jets. We show that the present theoretical uncertainties can be reduced with such data by a factor of 5. [less ▲]

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See detailNegative parity baryons in the 1/N_c expansion : the quark excitation versus the meson-nucleon resonance picture
Matagne, Nicolas; Stancu, Floarea ULg

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

In order to better understand the fundamental issue regarding the compatibility between the quark-shell picture and that of resonances in meson-nucleon scattering in large $N_c$ QCD we extend the work of ... [more ▼]

In order to better understand the fundamental issue regarding the compatibility between the quark-shell picture and that of resonances in meson-nucleon scattering in large $N_c$ QCD we extend the work of Cohen and Lebed on mixed symmetric $\ell $ = 1 baryons to analyze excited states with $\ell $ = 3. We give an explicit proof on the degeneracy of mass eigenvalues of a simple Hamiltonian including operators up to order $\mathcal{O}(N^0_c)$ \emph{i. e.} neglecting $1/N_c$ corrections in the quark-shell picture in the large $N_c$ limit. We obtain three degenerate multiplets formed of $\ell = 3$ states, as in the case of $\ell $ = 1 baryons. The compatibility between this picture and that of resonances in meson-nucleon scattering is discussed in the light of the present results. [less ▲]

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See detailpi N transition distribution amplitudes: Their symmetries and constraints from chiral dynamics
Pire, Bernard; Semenov-Tyan-Shanskiy, Kirill ULg; Szymanowski, Lech

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

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See detailProperties of the general N-Higgs-doublet model. I. The orbit space
Ivanov, Igor ULg; Nishi, Celso

in Physical Review. D : Particles and Fields (2010), 82(1), 0150141-16

We study the scalar sector of the general N-Higgs-doublet model via geometric constructions in the space of gauge orbits. We give a detailed description of the shape of the orbit space both for general N ... [more ▼]

We study the scalar sector of the general N-Higgs-doublet model via geometric constructions in the space of gauge orbits. We give a detailed description of the shape of the orbit space both for general N and, in more detail, for N=3. We also comment on remarkable analogies between the N-Higgs-doublet model and quantum information theory. [less ▲]

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See detailGroup theoretical study of nonstrange and strange mixed symmetric baryon states [Nc-1,1] in the 1/Nc expansion
Matagne, Nicolas; Stancu, Floarea ULg

in Physical Review. D : Particles and Fields (2010), 81

Using group theory arguments we extend and complete our previous work by deriving all SU(6) exact wave functions associated with the spectrum of mixed symmetric baryon states [Nc-1,1] in the 1/Nc ... [more ▼]

Using group theory arguments we extend and complete our previous work by deriving all SU(6) exact wave functions associated with the spectrum of mixed symmetric baryon states [Nc-1,1] in the 1/Nc expansion. The extension to SU(6) enables us to study the mass spectra of both strange and nonstrange baryons, while previous work was restricted to nonstrange baryons described by SU(4). The wave functions are specially written in a form to allow a comparison with the approximate, customarily used wave functions, where the system is separated into a ground state core and an excited quark. We show that the matrix elements of the flavor operator calculated with the exact wave functions acquire the same asymptotic form at large Nc, irrespective of the spin-flavor multiplet contained in [Nc-1,1], while with the approximate wave function one cannot obtain a similar behavior. The isoscalar factors of the permutation group of Nc particles derived here can be used in any problem where a given fermion system is described by the partition [Nc-1,1], and one fermion has to be separated from the rest. [less ▲]

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See detailHiggs boson masses of the general two-Higgs-doublet model in the Minkowski-space formalism
Degée, Audrey ULg; Ivanov, Igor ULg

in Physical Review. D : Particles and Fields (2010), 81

We study the masses of the Higgs bosons in the most general two-Higgs-doublet model in a basis-independent approach. We adapt the recently developed Minkowski-space formalism to this problem and calculate ... [more ▼]

We study the masses of the Higgs bosons in the most general two-Higgs-doublet model in a basis-independent approach. We adapt the recently developed Minkowski-space formalism to this problem and calculate traces of any power of the mass matrix in a compact and reparametrization-invariant form. Our results can be used to gain insight into the dynamics of the scalar sector of the general two-Higgs-doublet model. [less ▲]

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See detailEvolution of vacuum states and phase transitions in the two Higgs doublet model during cooling of the Universe
Ginzburg, Ilya; Ivanov, Igor ULg; Kanishev, Konstantin

in Physical Review. D : Particles and Fields (2010), 81

We consider the evolution of the ground state in the two Higgs doublet model during cooling down of the Universe after the big bang. Different regions in the space of free parameters of this model ... [more ▼]

We consider the evolution of the ground state in the two Higgs doublet model during cooling down of the Universe after the big bang. Different regions in the space of free parameters of this model correspond to different sequences of thermal phase transitions. We discuss different paths of thermal evolution and corresponding evolution of physical properties of the system for different modern values of the parameters. [less ▲]

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