Search

Glueballs are the most obvious, but this far not fully tested prediction of Quantum Chromodynamics. The lowest expected glueball states, in particular $0^{++}$ states are difficult to characterize, since they share the quantum numbers of the "vacuum" and of a number of possible quark-antiquark states. In this paper, we argue that the more easily identifiable exotics provide us with strong hints on the way to pursue the chase, and in particular the relation with quantum anomalies and the $\eta$ and $\eta '$ states., Comment: proceedings invited talk Corfu Summer Institute 2023

Glueballs are the most straightforward prediction of QCD, yet while they have likely been produced, none has been unequivocally identified. We pursue a backdoor approach through anomalies, and singularly the $\eta$ and $\eta$' which brings light to this irritating situation. In particular, we advocate to consider the full decay chain $J/\psi \rightarrow X \gamma , X \rightarrow \eta \eta'$ (into glue-rich states followed by glue-rich decays). We also suggest new BES III searches, namely for the $\pi_1$ into $\eta(') \pi^0$, (this would be the partner of their recently observed $\eta_1(1855)$). Another useful investigation would be for other channels (or semi-inclusive) $f_0 (1500)$ decays (see last section), Comment: Corfu workshop proceedings 2022

While Left-Right symmetry (space parity) breaking historically appeared as a surprise, we argue that the real wonder is its restoration in long-distance interactions (at least until we find electric dipole moments!)., Comment: 6pp, figures, presented at Corfu Summer Institute

At the beginning of 2016, LIGO reported the first-ever direct detection of gravitational waves. The measured signal was compatible with the merger of two black holes of about 30 solar masses, releasing about 3 solar masses of energy in gravitational waves. We consider the possible neutrino emission from a binary black hole merger relative to the energy released in gravitational waves and investigate the constraints coming from the non-detection of counterpart neutrinos, focusing on IceCube and its energy range. The information from searches for counterpart neutrinos is combined with the diffuse astrophysical neutrino flux in order to put bounds on neutrino emission from binary black hole mergers. Prospects for future LIGO observation runs are shown and compared with model predictions., Comment: 4 pages, 1 figure, to appear in Proceedings for the 52nd Rencontres de Moriond, EW session, 2017

The recent LIGO observation of gravitational waves from a binary black hole merger triggered several follow-up searches from both electromagnetic wave as well as neutrino observatories. Since in general, it is expected that all matter has been removed from the binary black hole environment long before the merger, no neutrino emission is expected from such mergers. Still, it remains interesting to test this hypothesis. The ratio of the energy emitted in neutrinos with respect to gravitational waves represents a useful parameter to constrain the environment of such astrophysical events. In addition to putting constraints by use of the non-detection of counterpart neutrinos, it is also possible to consider the diffuse neutrino flux measured by the IceCube observatory as the maximum contribution from an extrapolated full class of BBHs. Both methods currently lead to similar bounds on the fraction of energy that can be emitted in neutrinos. Nevertheless, combining both methods should allow to strongly constrain the source population in case of a future neutrino counterpart detection. The proposed approach can and will be applied to potential upcoming LIGO events, including binary neutron stars and black hole-neutron star mergers, for which a neutrino counterpart is expected., Comment: 8 pages, 2 figures. In Proceedings of the 35th International Cosmic Ray Conference (ICRC2017), Busan, Korea

Recently, the LIGO observatory reported the first direct observation of gravitational waves, with a signal consistent with a binary black hole merger. This detection triggered several follow-up searches for coincident emission in electromagnetic waves as well as neutrinos, but no such emission was found. In this article, the implications of the non-detection of counterpart neutrinos are investigated using general arguments. The results are interpreted with a parameter denoting the energy emitted in neutrinos relative to the energy emitted in gravitational waves. The bound on this parameter from the diffuse astrophysical neutrino flux detected by the IceCube Neutrino Observatory is discussed. It is found that, currently, the non-detection of counterpart neutrinos puts a bound comparable to the one from the diffuse astrophysical neutrino flux. This bound is then used to constrain the amount of matter in the black hole binary environment. Finally, the sensitivity to this parameter in future gravitational wave observation runs is investigated. It is shown how the detection of one or more neutrinos from a single merger would strongly constrain the source population and evolution., Comment: 12 pages, 5 figures. Added discussion on black hole mass distribution, as well as bounds on source evolution and amount of matter in the BBH environment. Accepted for publication by Phys. Rev. D

In this short presentation, we address two somewhat separate issues. The first one deals with the establishment (vs discovery) of what we call "physical laws". The discussion runs on a "successive approximations" approach, suited to our own thinking process, and aiming at the "simplest \emph{possible} formulation ", as opposed to the idea of pre-existing laws to be discovered. In the second part, we review briefly an approach to the (observed) metric originating from a short distance fractal structure, and remind how a symmetrical situation can arise from mere re-summations., Comment: 2 parts -- (i) provocative but pedagogical evocation of the establishment and nature of a physical law, (ii) discussion of the rise of a continuous-looking metric from a fractal ----- presented at "Spindel Fest", in honour of Philippe Spindel, Mons, June 2015

We study the mixing of the scalar glueball into the isosinglet mesons $f_0 (1370)$, $f_0(1500)$, and $f_0(1710)$ to describe the two-body decays to pseudoscalars. We use an effective Hamiltonian and employ the two-angle mixing scheme for $\eta$ and $\eta'$. In this framework, we analyse existing data and look forward to new data into $\eta$ and $\eta'$ channels. For now, the $f_0 (1710)$ has the largest glueball component and a sizable branching ratio into $\eta\eta'$, testable at BESIII., Comment: 7 pages, 1 figure. Included error bars from fit and added references. Matches PRD version

Electromagnetic properties of neutrinos, if ever observed, could help to decide the Dirac versus Majorana nature of neutrinos. We show that the magnetic moments of Majorana neutrinos have to fulfill triangle inequalities, $|\mu_{\nu_\tau}|^2 \leq |\mu_{\nu_\mu}|^2 +|\mu_{\nu_e}|^2$ and cyclic permutations, which do not hold for Dirac neutrinos. Observing a violation of these inequalities, e.g. by measuring the magnetic moment of $\nu_\tau$ at SHiP, would thus strongly hint either at the Dirac nature of neutrinos or at the presence of at least one extra light sterile mode., Comment: 10 pages, 1 figure. Extended discussion of sterile neutrinos; accepted by PRD

We consider the phenomenology of new neutral gauge bosons with flavour non-diagonal couplings to fermions, inherent in 6D models explaining successfully the hierarchy of masses as well as the mixing for quarks, charged leptons and neutrinos (this model can in particular be credited with the correct prediction of the neutrino mixing angle $\theta_{13}$). We present a general relation between masses of new gauge bosons and their couplings to fermions. We show that in the current realization of the model, the new heavy bosons are unreachable at LHC but argue why the constraint could be relaxed in the context of a different realization. In view of a more systematic study, we use an effective model inspired by the above to relate directly rare meson decays to possible LHC observations. In terms of effective Lagrangians, this can be seen as the introduction in the model of only one overall scaling parameter to extend our approach without modifying the 4D (gauge) structure., Comment: 14 pages, 1 figure

In this short presentation, we remind of significant unknowns regarding the distribution of Dark Matter in our immediate neighborhood, and review the recent improvements in the obtained limits on its abundance., Comment: 6 pages 1 figure uses \psfrag Corfu Summer Institute Proceedings

We address the question, how general is the gauge sector in extra-dimensional models which explain hierarchies of masses and mixings of quarks, charged leptons and neutrinos in terms of a single family of multidimensional fermions. We give qualitative arguments that though there are a plethora of possible variations, they do not result in drastical changes of phenomenology., Comment: 13 pages. To be published in a special issue of JETP dedicated to the 60th birthday of Valery Rubakov

One of the Sakharov's condition for baryogenesis is the violation of both C and CP. In the Standard Model, gauge interactions break maximally C, but CP is only broken through the Yukawa couplings in the poorly understood scalar sector. In extra-dimensional models, extra components of gauge fields behave as scalars in 4D and can acquire effective vev's through (finite) quantum effects (Hosotani mechanism). This mechanism is used to build a toy model with 2 extra-dimensions compactified on a flat torus $T^2$, where a SU(2) gauge symmetry is broken to U(1) and CP violation (in 4D) is expected. This is verified by computing a non-vanishing electric dipole moment., Comment: 16 pages, 24 figures, final version accepted for publication in JHEP

The discovery of the Standard Model Scalar Boson (Brout-Englert-Higgs particle) opens a new field of research, namely the structure of the scalar sector. Numerous extensions exist, and imply extra particles, including additional scalars. Two main alleys are open to investigate such deviations from the minimal standard model: precision measurements could indicate a deviation from the usual expectations, or a direct discovery of new scalar partners (or other particles) would establish an alternative. In this short note, we concentrate on a very simple model, for which the respective reaches of the two approaches can be compared. This note also provides a strong incentive to pursue searches for extra "Standard Model Scalar-like" particles in the whole available energy spectrum., Comment: pdflatex, 8 pages, 4 figs; updated references, added figures presented at IAP-Solvay Workshop "Facing the Scalar Sector", Brussels, May 29-31 -- current version : updated to take into account H2 -> 2 H1 decay

We discuss the possibility that the limiting speed (c_l) appearing in Lorentz equations might be different i.e., slightly larger than the observed speed of light (c_n). We show that such a possibility can be tested by state-of-the-art Michelson-Morley experiments, but also by careful measurement of neutrino speeds. It would indeed suffice to show that c_n < c_neutrinos <= c_l. Quite interestingly, current limits from both approaches are competitive, in some circumstances. We also comment on competing tests using gamma-ray burst, assuming a dispersive character for the propagation of light., Comment: 8 pages, 1 figure. Updated was latest ICARUS results; matches version to be published in EPJC

In the vortex background on a sphere, a single 6-dimensional fermion family gives rise to 3 zero-modes in the 4-dimensional point of view, which may explain the replication of families in the Standard Model. Previously, it had been shown that realistic hierarchical mass and mixing patterns can be reproduced for the quarks and the charged leptons. Here, we show that the addition of a single heavy 6-dimensional field that is gauge singlet, unbound to the vortex, and embedded with a bulk Majorana mass enables to generate 4D Majorana masses for the light neutrinos through the see-saw mechanism. The scheme is very predictive. The hierarchical structure of the fermion zero-modes leads automatically to an inverted pseudo-Dirac mass pattern, and always predicts one maximal angle in the neutrino see-saw matrix. It is possible to obtain a second large mixing angle from either the charged lepton or the neutrino sector, and we demonstrate that this model can fit all observed data in neutrino oscillations experiments. Also, U_{e3} is found to be of the order ~0.1., Comment: 23 pages, 1 figure