High Energy Physics Phenomenology

We consider the directs-channel gravitational production of dark matter during the reheating process. Independent of the identity of the dark matter candidate or its non-gravitational interactions, the gravitational process is always present and provides a minimal production mechanism. During reheating, a thermal bath is quickly generated with a maximum temperatureTmax, and the temperature decreases as the inflaton continues to decay until the energy densities of radiation and inflaton oscillations are equal, atTRH. During these oscillations,s-channel gravitational production of dark matter occurs. We show that the abundance of dark matter (fermionic or scalar) depends primarily on the combinationT4max/TRHM3P. We find that a sufficient density of dark matter can be produced over a wide range of dark matter masses: from a GeV to a ZeV.

We propose leveraging our proficiency for detecting Higgs resonances by using the Higgs as a tagging object for new heavy physics. In particular, we argue that searches for exotic Higgs production from decays of color-singlet fields with electroweak charges could beat current searches at the LHC which look for their decays to vectors. As an example, we study the production and decay of vector-like leptons which admit Yukawa couplings with SM leptons. We find that bounds from Run 2 searches are consistent with anywhere from hundreds to many thousands of Higgses having been produced in their decays over the same period, depending on the representation. Dedicated searches for these signatures may thus be able to significantly improve our reach at the electroweak energy frontier.

This write-up of the ICHEP plenary "Heavy Ions - theory" focusses on some recent LHC discoveries and future opportunities in heavy ion physics (HIP) that are at the intersection with high energy physics (HEP).

We present predictions for hadronic decays of the Higgs boson at next-to-next-to-leading order (NNLO) in QCD matched with parton shower based on the POWHEG framework. Those include decays into bottom quarks with full bottom-quark mass dependence, light quarks, and gluons in the heavy top quark effective theory. Our calculations describe exclusive decays of the Higgs boson with leading logarithmic accuracy in the Sudakov region and next-to-leading order (NLO) accuracy matched with parton shower in the three-jet region, with normalizations fixed to the partial width at NNLO. We estimated remaining perturbative uncertainties taking typical event shape variables as an example and demonstrated the need of future improvements on both parton shower and matrix element calculations. The calculations can be used immediately in evaluations of the physics performances of detector designs for future Higgs factories.

We study the discovery potential of the non-Standard Model (SM) heavy Higgs bosons in the Two-Higgs-Doublet Models (2HDMs) at a multi-TeV muon collider and explore the discrimination power among different types of 2HDMs. We find that the pair production of the non-SM Higgs bosons via the universal gauge interactions is the dominant mechanism once above the kinematic threshold. Single Higgs boson production associated with a pair of heavy fermions could be important in the parameter region with enhanced Yukawa couplings. For both signal final states,μ+μ??annihilation channels dominate over the vector boson fusion (VBF) processes, except at high center of mass energies where the VBF processes receive large logarithmic enhancement with the increase of energies. Single Higgs bosons-channel production inμ+μ??-annihilation via the radiative return can also be important for the Type-L 2HDM in the very largetanβregion, extending the kinematic reach of the heavy Higgs boson mass to the collider energy. Considering both the production and decay of non-SM Higgs bosons, signals can be identified over the Standard Model backgrounds. Different types of 2HDMs can be distinguishable for moderate and large values oftanβ.

This paper investigates thee+e???�Zhsensitivity for Higgs boson's rare decay into heavy neutrinosh?�NNat the proposed electron-positron collider, with the focus on multi-lepton final states that contain same-sign lepton pairs.h?�NNdecay can derive from Higgs boson's mixing with new physics scalar(s) that is complementary to the contribution from active-sterile neutrino mixings. We analyze the semileptonic, fully leptonic and mixedNNdecay scenarios, and categorize the signal on the number of leptons in the final state:??±??±with at least 3 jets,??±??±??with at least 2 jets, ande±e±μ??μ??plus with at least 1 jet, each containing one or two same-sign dilepton system(s). Selection cuts are optimized for the presence of the associatedZboson, which leads to additional backgrounds at thee+e??collider. The Standard Model background channels are systematically analyzed. Sensitivity limits onh?�NNbranching fractions are derived for signals with 2-4 final leptons assuming the heavy neutrino masses are between 10 and 60 GeV. With 240 GeV center-of-mass energy and 5.6 ab??design luminosity,h?�NNbranching fraction can be probed to2?10??in2??and3??channels, and6?10??in the4??channel at95%credence level.3??4??channels expect one or fewer background event, and their sensitivities saturate the statistic limit at 5.6 ab??luminosity. A same-sign trilepton (??±??±??±) signal in the3??channel is also discussed.

We study a "heavy" QCD axion whose coupling to the standard model is dominated byaGG?but withma??m?f?/fa. This is well motivated as it can solve the strong CP problem while evading the axion quality problem. It also poses interesting challenges for its experimental search due to its suppressed couplings to photons and leptons. Such axion with mass around a GeV is kinematically inaccessible or poorly constrained by most experimental probes except B-factories. We studyB?�Katransitions as a powerful probe of the heavy QCD axion by performing necessary 2-loop calculations for the first time, together with some improvement on the existing analysis strategy. We find some of the existing limits are enhanced by at least an order of magnitude. We also demonstrate that the bounds are robust against unknown UV physics. For forthcoming data sets of the Belle II experiment, we provide a projection thatfaof a few TeV is within its future reach, which is relevant to the quality problem.

The impact of momentum anisotropy on the heavy quark transport coefficients due to collisional and radiative processes in the QCD medium has been studied within the ambit of kinetic theory. Anisotropic aspects (momentum) are incorporated into the heavy quark dynamics through the non-equilibrium momentum distribution function of quarks, antiquarks, and gluons. These non-equilibrium distribution functions that encode the physics of momentum anisotropy and turbulent chromo-fields have been obtained by solving the ensemble-averaged diffusive Vlasov-Boltzmann equation. The momentum dependence of heavy quark transport coefficients in the medium is seen to be sensitive to the strength of the anisotropy for both collisional and radiative processes. In addition, the collisional and radiative energy loss of the heavy quark in the anisotropic hot QCD medium have been analyzed. The effects of anisotropy on the drag and diffusion coefficients are observed to have a visible impact on the nuclear suppression factor both at the RHIC and LHC.

In order to explore the potential of beta-decay experiments to detect relic neutrinos (CνB), we study the intrinsic irreducible uncertainty in the energy of electrons resulting from the zero-point motion of the emitter. Motivated by the PTOLEMY proposal, we consider the case of Tritium adsorbed on graphene. We show that in this case, the intrinsic uncertainty is larger than the target resolution of the measurement. We discuss nevertheless that the ambitious goal of detecting CνB could still be achieved with further refinement of the experimental design. One option is to substitute Tritium with a heavier emitter; another is to design an angle-resolved detection setup where the emitter has a higher degree of mobility along the substrate.

Motivated by the successful interpretation of these observedPcandPcsstates under the meson-baryon molecular picture, we systematically investigate the possible hidden-charm molecular pentaquark states with triple strangeness which is due to theΩ(??cD¯(??sinteractions. We perform a dynamical calculation of the possible hidden-charm molecular pentaquarks with triple strangeness by the one-boson-exchange model, where theS-Dwave mixing effect and the coupled channel effect are taken into account in our calculation. Our results suggest that theΩcD¯??sstate withJP=3/2??and theΩ??cD¯??sstate withJP=5/2??can be recommended as the candidates of the hidden-charm molecular pentaquark with triple strangeness. Furthermore, we discuss the two-body hidden-charm strong decay behaviors of these possible hidden-charm molecular pentaquarks with triple strangeness by adopting the quark-interchange model. These predictions are expected to be tested at the LHCb, which can be as a potential research issue with more accumulated experimental data in near future.