High Energy Physics Phenomenology

The topological structure of vacuum is the cornerstone of non-Abelian gauge theories describing strong and electroweak interactions within the standard model of particle physics. However, transitions between different topological sectors of the vacuum (believed to be at the origin of the baryon asymmetry of the Universe) have never been observed directly. An experimental observation of such transitions in Quantum Chromodynamics (QCD) has become possible in heavy-ion collisions, where the chiral magnetic effect converts the chiral asymmetry (generated by topological transitions in hot QCD matter) into an electric current, under the presence of the magnetic field produced by the colliding ions. The Relativistic Heavy Ion Collider program on heavy-ion collisions such as the Zr-Zr and Ru-Ru isobars, thus has the potential to uncover the topological structure of vacuum in a laboratory experiment. This discovery would have far-reaching implications for the understanding of QCD, the origin of the baryon asymmetry in the present-day Universe, and for other areas, including condensed matter physics.

We study the time evolution of the chirality imbalancen5and the chiral magnetic effect (CME) under the external parallel electromagnetic fields without assuming the artificial chiral asymmetric source. We adopt the time-dependent Sauter-type electric and constant magnetic field, and obtain analytical solutions of the Dirac equation for a massive fermion. We use the point-split regularization to calculate the vacuum contribution in the gauge invariant way. As a result, we find thatn5and CME current increase substantially as the electric field increases, and stay finite after the electric field is switched off. The chirality imbalance and CME current are shown to consist of a dominant contribution, which is essentially proportional to relativistic velocity, and a small oscillating part. We find a simple analytical relation betweenn5and the fermion pair-production rate from the vacuum. We also discuss dynamical origin of the chirality imbalance in detail.

QED perturbation theory has been conjectured to break down in sufficiently strong backgrounds, obstructing the analysis of strong-field physics. We show that the breakdown occurs even in classical electrodynamics, at lower field strengths than previously considered, and that it may be cured by resummation. As a consequence, an analogous resummation is required in QED. A detailed investigation shows, for a range of observables, that unitarity removes diagrams previously believed to be responsible for the breakdown of QED perturbation theory.

If neutrinos are Dirac, the conditions for cobimaximal mixing, i.e.θ23=?/4andδCP=±?/2in the3?3neutrino mixing matrix, are derived. One example withA4symmetry and radiative Dirac neutrino masses is presented.

In our previous studies (see [1] and references therein) we developed a new theoretical framework that enabled one to consider a new mechanism of neutrino quantum decoherence engendered by the neutrino radiative decay. In parallel, another framework was developed (see [2] and references therein) for the description of the neutrino quantum decoherence due to the non-forward neutrino scattering processes. Both mechanisms are described by the master equations in the Lindblad form.We study the influence of the neutrino quantum decoherence on collective neutrino oscillations. In the present studies we are are not interested in a specific mechanism of neutrino quantum decoherence. Therefore, we use the general Lindblad master equation for the description of the neutrino quantum decoherence and do not fix an analytical expressions for the decoherence and relaxation parameters.

Low-scale baryogenesis could be discovered atB-factories and the LHC. In theB-Mesogenesis paradigm, the CP violating oscillations and subsequent decays ofBmesons in the early Universe simultaneously explain the origin of the baryonic and the dark matter of the Universe. This mechanism for baryo- and dark matter-genesis fromBmesons gives rise to distinctive signals at collider experiments, which we scrutinize in this paper. We study CP violating observables in theB0q??B¯0qsystem, discuss current and expected sensitivities for the exotic decays ofBmesons into a visible baryon and missing energy, and explore the implications of direct searches for a TeV-scale colored scalar at the LHC and in meson-mixing observables. Remarkably, we conclude that a combination of measurements at BaBar, Belle, Belle II, LHCb, ATLAS and CMS can fully testB-Mesogenesis.

We consider effects of coloured scalar mediators in decaysc?�uinvisibles. In particular, in these processes, as invisibles, we consider massive right-handed fermions. The coloured scalarS¯1??3¯,1,??/3), due to its coupling to weak singlets up-quarks and invisible right-handed fermions (?), is particularly interesting. Then, we considerR~2??3¯,2,1/6), which as a weak doublet is a subject of severe low-energy constraints. The?mass is considered in the range(mK??m?)/2??m???mD??m?)/2. We determine branching ratios forD?��??¯,D?��??¯γandD?�π??for several?masses, using most constraining bounds. ForS¯1, the most constraining isD0??D¯0mixing, while in the case ofR~2the strongest constraint comes fromB?�Kmissingenergy. We find in decays mediated byS¯1that branching ratios can beB(D?��??¯)<10??form?=0.8GeV,B(D?��??¯γ)??10??form?=0.18GeV, whileB(D+???+??¯)can reach??10??form?=0.18GeV. In the case ofR~2these decay rates are very suppressed. We find that future tau-charm factories and Belle II experiments offer good opportunities to search for such processes. BothS¯1andR~2might have masses within LHC reach.

Ensemble learning is a technique where multiple component learners are combined through a protocol. We propose an Ensemble Neural Network (ENN) that uses the combined latent-feature space of multiple neural network classifiers to improve the representation of the network hypothesis. We apply this approach to construct an ENN from Convolutional and Recurrent Neural Networks to discriminate top-quark jets from QCD jets. Such ENN provides the flexibility to improve the classification beyond simple prediction combining methods by linking different sources of error correlations, hence improving the representation between data and hypothesis. In combination with Bayesian techniques, we show that it can reduce epistemic uncertainties and the entropy of the hypothesis by simultaneously exploiting various kinematic correlations of the system, which also makes the network less susceptible to a limitation in training sample size.

The high luminosity that will be accumulated at the LHC will enable precise differential measurements of the hadronic production of a top--antitop-quark pair in association with aWboson. Therefore, an accurate description of this process is needed for realistic final states. In this work we combine for the first time the NLO QCD and electroweak corrections to the full off-shelltt¯W+production at the LHC in the three-charged-lepton channel, including all spin correlations, non-resonant effects, and interferences. To this end, we have computed the NLO electroweak radiative corrections to the leading QCD order as well as the NLO QCD corrections to both the QCD and the electroweak leading orders.

We study theD+???+ηηandD+???+?0ηreactions, which are single Cabibbo suppressed and can proceed both through internal and external emission. The primary mechanisms at quark level are considered, followed by hadronization to produce three mesons in theD+decay, and after that the final state interaction of these mesons leads to the production of thea0(980)resonance, seen in the?+η,?0ηmass distributions. The theory has three unknown parameters to determine the shape of the distributions and the ratio between theD+???+ηηandD+???+?0ηrates. This ratio restricts much the sets of parameters but there is still much freedom leading to different shapes in the mass distributions. We call for a measurement of these mass distributions that will settle the reaction mechanism, while at the same time provide relevant information on the way that thea0(980)resonance is produced in the reactions.