High Energy Physics Phenomenology

The electromagnetic properties of neutrinos have attracted considerable attention from researchers for many decades (see [1] for a review). However, until recently, there was no indication in favour of nonzero electromagnetic properties of neutrinos either from laboratory experiments with ground-based neutrino sources or from observations of astrophysical neutrino fluxes. The situation changed after the XENON collaboration reported [2] results of the search for new physics with low-energy electronic recoil data recorded with the XENON1T detector. The results show an excess of events over the known backgrounds in the recoil energy which, as one of the possible explanations, admit the presence of a sizable neutrino magnetic moment, the value of which is of the order of the existing laboratory limitations. In these short notes we give a brief introduction to neutrino electromagnetic properties and focus on the most important constraints on neutrino magnetic moments, charge radii and millicharges from the terrestrial experiments and astrophysical considerations. The promising new possibilities for constraining neutrino electromagnetic properties in future experiments are also discussed.

We investigate the electromagnetic transitions of the singly charmed baryons with spin 3/2, based on a pion mean-field approach, also known as the chiral quark-soliton model, taking into account the rotational1/Nccorrections and the effects of flavor SU(3) symmetry breaking. We examine the valence- and sea-quark contributions to the electromagnetic transition form factors and find that the quadrupole form factors of the sea-quark contributions dominate over those of the valence-quark ones in the smallerQ2region, whereas the sea quarks only provide marginal contributions to the magnetic dipole transition form factors of the baryon sextet with spin 3/2. The effects of the flavor SU(3) symmetry breaking are in general very small except for the forbidden transition?0cγ?????cbyU-spin symmetry. We also discuss the widths of the radiative decays for the baryon sextet with spin 3/2, comparing the present results with those from other works.

The recently improved observation of the fine structure constant has led to a negative2.4?anomaly of electrong??. Combined with the long-existing positive3.7?discrepancy of the muon anomalous magnetic moment, it is interesting and difficult to explain these two anomalies with a consistent model without introducing flavor violations. We show that they can be simultaneously explained in the inverse seesaw extended next-to-minimal supersymmetric standard model (ISS-NMSSM) by the Higgsino--sneutrino contributions to(g??)eand(g??)μ. The spectrum features prefer lightμ, which can predictmZnaturally, and it is not difficult to obtain a?-type sneutrino dark matter candidate that is compatible with the observed dark matter relic density and the bounds from dark matter direct detection experiments. Due to the compressed spectra and the undetectable decay mode of selectrons, they can evade the current Large Hadron Collider (LHC) constraints.

Methods for extracting the?(3770)??e+e??decay width from the data on the reaction cross sectione+e???�DD¯are discussed. Attention is drawn to the absence of the generally accepted method for determining??(3770)e+e??in the presence of interference between the contributions of the?(3770)resonance and background. It is shown that the model for the experimentally measuredDmeson form factor, which satisfies the requirement of the Watson theorem and takes into account the contribution of the complex of the mixed?(3770)and?(2S)resonances, allows uniquely determine the value of??(3770)e+e??by fitting. The??(3770)e+e??values found from the data processing are compared with the estimates in the potential models.

The differential cross sectiond?/dq2of diffractive electroproduction of heavy quarkonia on protons is a sensitive study tool for the interaction dynamics within the dipole representation. Knowledge of the transverse momentum transferq??provides a unique opportunity to identify the reaction plane, due to a strong correlation between the directions ofq??and impact parameterb??. On top of that, the elastic dipole-proton amplitude is subject to a strong correlation betweenb??and dipole orientationr??. Most of models forb-dependent dipole cross section either completely miss this information, or make unjustified assumptions. We perform calculations basing on a realistic model forr??-b??correlation, which significantly affect theq-dependence of the cross section, in particular the ratio of???(2S)toJ/?yields. We rely on realistic potential models for the heavy quarkonium wave function, and the Lorentz-boosted Schrödinger equation. Good agreement with data onq-dependent diffractive electroproduction of heavy quarkonia is achieved.

We use theSU(5)model to show the presence in grand unified theories of an electroweak monopole and a magnetic dumbbell ("meson") made up of a monopole-antimonopole pair connected by aZ-magnetic flux tube. The monopole is associated with the spontaneous breaking of the weakSU(2)Lgauge symmetry by the induced vacuum expectation value of a heavy scalarSU(2)Ltriplet with zero weak hypercharge contained in the adjoint Higgs 24-plet. This monopole carries a Coulomb magnetic charge of(3/4)(2?/e)as well asZ-magnetic charge, where2?/edenotes the unit Dirac magnetic charge. Its total magnetic charge is3/8????????(4?/e), which is in agreement with the Dirac quantization condition. The monopole weighs about 700 GeV, but because of the attachedZ-magnetic tube it exists, together with the antimonopole, in a magnetic dumbbell configuration whose mass is expected to lie in the TeV range. The presence of these topological structures inSU(5)andSO(10)and in their supersymmetric extensions provides an exciting new avenue for testing these theories in high-energy colliders.

An exploratory study of the time-like pion electromagnetic form factor in a Poincaré-covariant bound state formalism in the isospin symmetric limit is presented. Starting from a quark interaction kernel representing gluon-intermediated interactions for valence-type quarks, non-valence effects are included by introducing pions as explicit degrees of freedom. The two most important qualitative aspects are, in view of the presented study, the opening of the dominant?-meson decay channel and the presence of a multi-particle branch cut setting in when the two-pion threshold is crossed. Based on a recent respective computation of the quark-photon vertex, the pion electromagnetic form factor for space-like and time-like kinematics is calculated. The obtained results for its absolute value and its phase compare favorably to the available experimental data, and they are analyzed in detail by confronting them to the expectations based on an isospin-symmetric version of a vector-meson dominance model.

ThepTdistributions of theK0- and?- mesons produced in theppcollisions ats??=2.76TeVhave been analyzed by fitting them using the exponential function. It was observed that the distributions contain severalpTregions similar to the cases with the charged particles,?0- andη- mesons produced in the same events. These regions could be characterized using three variables: the length of the regionLcKand free fitting parametersacKandbcK. It was observed that the values of the parameters as a function of energy grouped around certain lines and there are jump-like changes. These observations together with the effect of existing the severalpTregions can say on discrete energy dependencies for theLcK,acKandbcK. The lengths of the regions increase with the mass of the particles. This increase gets stronger with energy. The mass dependencies of the parametersacKandbcKshow a regime change at a mass??00MeV/c2. According to the phenomenology of string theory, these results could be explained by two processes occurring simultaneously: string hadronization and string breaking. In the experiment we can only measure the spectrum of the hadronized particles, since we cannot access the spectrum of the strings themselves. The string breaking effect could be a signal of string formations and the reason behind the observation of severalpTregions and the jump-like changes for the characteristics of the regions.

The energy-energy correlator (EEC) is an event shape observable which probes the angular correlations of energy depositions in detectors at high energy collider facilities. It has been investigated extensively in the context of precision QCD. In this work, we introduce a novel definition of EEC adapted to the Breit frame in deep-inelastic scattering (DIS). In the back-to-back limit, the observable we propose is sensitive to the universal transverse momentum dependent (TMD) parton distribution functions and fragmentation functions, and it can be studied within the traditional TMD factorization formalism. We further show that the new observable is insensitive to experimental pseudorapidity cuts, often imposed in the Laboratory frame due to detector acceptance limitations. In this work the singular distributions for the new observable are obtained in soft collinear effective theory up toO(α3s)and are verified by the full QCD calculations up toO(α2s). The resummation in the singular limit is performed up to next-to-next-to-next-to-leading logarithmic accuracy. After incorporating non-perturbative effects, we present a comparison of our predictions to PYTHIA 8 simulations.

Collective neutrino oscillations play a crucial role in transporting lepton flavor in astrophysical settings, such as supernovae, where the neutrino density is large. In this regime, neutrino-neutrino interactions are important and simulations in mean-field approximations show evidence for collective oscillations occurring at time scales much larger than those associated with vacuum oscillations. In this work, we study the out-of-equilibrium dynamics of a corresponding spin model using Matrix Product States and show how collective bipolar oscillations can be triggered by quantum fluctuations if appropriate initial conditions are present. The origin of these flavor oscillations, absent in the mean-field, can be traced to the presence of a dynamical phase transition, which drastically modifies the real-time evolution of the entanglement entropy. We find entanglement entropies scaling at most logarithmically in the system size, suggesting that classical tensor network methods could be efficient in describing collective neutrino dynamics more generally.