High Energy Physics Phenomenology

We study models with severalSU(2)scalar doublets where the inert doublets have a non-minimal coupling to gravity and play the role of the inflaton. We allow for this coupling to be complex, thereby introducing CP-violation -- a necessary source of the baryon asymmetry -- in the Higgs-inflaton couplings. We investigate the inflationary dynamics of the model and discuss how the CP-violation of the model is imprinted on the particle asymmetries after inflation in the hot big bang universe.

From the amplitude analysis of theD+s???+?0ηdecay, the BESIII Collaboration firstly observed theD+s??a0(980)+?0andD+s??a0(980)0?+decay modes, which are expected to occur through the pureW-annihilation processes. The measured branching fractionB[D+s??a0(980)+(0)?0(+),a0(980)+(0)???+(0)η]is, however, found to be larger than those of knownW-annihilation decays by one order of magnitude. This apparent contradiction can be reconciled if the two decays are induced by internalW-conversion or externalW-emission mechanisms instead ofW-annihilation mechanism. In this work, we propose that theD+sdecay proceeds via both the external and internalW-emission instead ofW-annihilation mechanisms. In such a scenario, we perform a study of theD+s???+?0ηdecay by taking into account the contributions from the tree diagramD+s???+η???+?0ηand the intermediate?+ηandK??K¯/KK¯??triangle diagrams. The intermediatea0(980)state can be dynamically generated from the final state interactions of coupledKK¯and?ηchannels, and it is shown that the experimental data can be described fairly well, which supports the interpretation ofa0(980)as a molecular state.

We report on an interesting realization of the QCD axion, with mass in the rangeO(10)MeV. It has previously been shown that although this scenario is stringently constrained from multiple sources, the model remains viable for a range of parameters that leads to an explanation of the Atomki experiment anomaly. In this article we study in more detail the additional constraints proceeding from recent low energy experiments and study the compatibility of the allowed parameter space with the one leading to consistency of the most recent measurements of the electron anomalous magnetic moment and the fine structure constant. We further provide an ultraviolet completion of this axion variant and show the conditions under which it may lead to the observed quark masses and CKM mixing angles, and remain consistent with experimental constraints on the extended scalar sector appearing in this Standard Model extension. In particular, the decay of the Standard Model-like Higgs boson into two light axions may be relevant and leads to a novel Higgs boson signature that may be searched for at the LHC in the near future.

We investigate the cosmological stability of light bosonic dark matter carrying a tiny electric charge. In the wave-like regime of high occupation numbers, annihilation into gauge bosons can be drastically enhanced by parametric resonance. The millicharged particle can either be minimally coupled to photons or its electromagnetic interaction can be mediated via kinetic mixing with a massless hidden photon. In the case of a direct coupling current observational constraints on the millicharge are stronger than those arising from parametric resonance. For the (theoretically preferred) case of kinetic mixing large regions of parameter space are affected by the parametric resonance leading at least to a fragmentation of the dark matter field if not its outright destruction.

We present a comprehensive analysis of the potential sensitivity of the Electron-Ion Collider (EIC) to charged lepton flavor violation (CLFV) in the channelep?�τX, within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). We compute the relevant cross sections to leading order in QCD and electroweak corrections and perform simulations of signal and SM background events in various?decay channels, suggesting simple cuts to enhance the associated estimated efficiencies. To assess the discovery potential of the EIC in?-etransitions, we study the sensitivity of other probes of this physics across a broad range of energy scales, frompp?�e?Xat the Large Hadron Collider to decays ofBmesons and?leptons, such as??�eγ,??�e??+????, and crucially the hadronic modes??�eYwithY?�{?,K,??,K?,...}. We find that electroweak dipole and four-fermion semi-leptonic operators involving light quarks are already strongly constrained by?decays, while operators involving thecandbquarks present more promising discovery potential for the EIC. An analysis of three models of leptoquarks confirms the expectations based on the SMEFT results. We also identify future directions needed to maximize the reach of the EIC in CLFV searches: these include an optimization of the?tagger in hadronic channels, an exploration of background suppression through taggingbandcjets in the final state, and a global fit by turning on all SMEFT couplings, which will likely reveal new discovery windows for the EIC.

A model-independent analysis of a non-standard scalar contribution to the pion decay in a lepton and a neutrino is presented. We discuss the necessity of such scalars in many models beyond the standard model to conclude that an entirely new range of masses and couplings associated with the new scalar, entirely apart from standard contributions alone, is compatible with experimental results. The new range for the coupling constant and mass of the charged scalar is a consequence of suitable cancellations of standard and non-standard contributions to the pion decay.

In this work, we extended our statistical model with charmed and bottomed hadrons, and fit the quark creational probabilities for the heavy quarks, using low energy inclusive charmonium and bottomonium data. With the finalized fit for all the relevant types of quarks (up, down, strange, charm, bottom) at the energy range from a few GeV up to a few tens of GeV's, the model is now considered complete. Some examples are also given for proton-proton, pion-proton, and proton-antiproton collisions with charmonium, bottomonium, and open charm hadrons in the final state.

By extending a previously proposed conformal gauge mediation model, we construct a gauge-mediated SUSY breaking (GMSB) model where a SUSY-breaking scale, a messenger mass, theμ-parameter and the gravitino mass in a minimal supersymmetric (SUSY) Standard Model (MSSM) are all explained by a single mass scale, a R-symmetry breaking scale. We focus on a low scale SUSY-breaking scenario with the gravitino massm3/2=O(1)eV, which is free from the cosmological gravitino problem and relaxes the fine-tuning of the cosmological constant. Both the messenger and SUSY-breaking sectors are subject to a hidden strong dynamics with the conformality above the messenger mass threshold (and hence the name of the model "strongly interacting conformal gauge mediation"). In our model, the Higgs B-term is suppressed and a largetanβis predicted, resulting in the relatively light second CP-even Higgs and the CP-odd Higgs with a sizable production cross section. These Higgs bosons can be tested at future LHC experiments.

We investigate two different models. In one of them massive fermions interact with a massive scalar field and in the other the fermion field is in an electrical field (QED2). The chiral condensates are calculated in one-loop approximation. We found that the chiral condensate in the case of the Yukawa interaction the fermions and scalar field does not vanish if the mass of the fermion field tends to zero. The chiral condensate disappears in QED2, if the fermion mass is zero.

We outline and review the computations of polarized and unpolarized nucleon structure functions within the bosonized Nambu-Jona-Lasinio chiral soliton model. We focus on a consistent regularization prescription for the Dirac sea contribution and present numerical results from that formulation. We also reflect on previous calculations on quark distributions in chiral quark soliton models and attempt to put them into perspective.