High Energy Physics Phenomenology

We reanalyze the experimental NMC data on the nonsinglet structure functionFp2??Fn2and E866 data on the nucleon sea asymmetryd¯/u¯using the truncated moments approach elaborated in our previous papers. With help of the special truncated sum one can overcome the problem of the unavoidable experimental restrictions on the Bjorkenxand effectively study the fundamental sum rules for the parton distributions and structure functions. Using only the data from the measured region ofx, we obtain the Gottfried sum??10Fns2/xdxand the integrated nucleon sea asymmetry??10(d¯??u¯)dx. We compare our results with the reported experimental values and with the predictions obtained for different global parametrizations for the parton distributions. We also discuss the discrepancy between the NMC and E866 results on??10(d¯??u¯)dx. We demonstrate that this discrepancy can be resolved by taking into account the higher-twist effects.

In high energy particle collisions the shape of the event, i.e. the relative distribution of particles in momentum space, is often used to try to select events with certain topologies. It is claimed that an event shape observable like transverse sphericity is able to discriminate between jet-like events and events that are dominated by soft production from the underlying event.In this paper we investigate the relationship between the shape of the event and the number of jets found in the respective event for bothe+e??and pp collisions using the PYTHIA model. Ine+e??collisions, we find that the transverse sphericity of the event can be used effectively to either enhance or suppress the fraction of jets found in the selected sample, and can even discriminate between single, two, and multi-jet topologies. However, contrary to current literature, we find that in pp collisions this does not hold. It is shown that the transverse sphericity as well as the particle multiplicity is sensitive to the number of multi-parton interactions.

We perform a calculation of the one- and two-point correlation functions of energy density and axial charge deposited in the Glasma in the initial stage of a heavy ion collision at finite proper time. We do this by describing the initial stage of heavy ion collisions in terms of freely-evolving classical fields whose dynamics obey the linearized Yang-Mills equations. Our approach allows us to systematically resum the contributions of high momentum modes that would make a power series expansion in proper time divergent. We evaluate the field correlators in the MV model using the Glasma Graph approximation, but our approach for the time dependence can be applied to a general four-point function of the initial color fields. Our results provide analytical insight into the pre-equilibrium phase of heavy ion collisions without requiring a numerical solution to the Yang-Mills equations.

We study a class of gauge groups that can automatically yield a perturbatively exact Peccei-Quinn symmetry, and we outline a model in which the axion quality problem is solved at all operator dimensions. Gauge groups belonging to this class can also enforce and protect accidental symmetries of the clockwork type, and we present a toy model where an `invisible' axion arises from a single breaking of the gauge and global symmetries.

We present new exact solutions of the Landau-Lifshitz and higher-order Landau-Lifshitz equations describing particle motion, with radiation reaction, in intense electromagnetic fields. Through these solutions and others we compare the phenomenological predictions of different equations in the context of the conjectured `radiation-free direction' (RFD). We confirm analytically in several cases that particle orbits predicted by the Landau-Lifshitz equation indeed approach the RFD at extreme intensities, and give time-resolved signals of this behaviour in radiation spectra.

The exceptional region of the parameter space (ERPS) of the two Higgs doublet model (2HDM) is defined to be the parameter regime where the scalar potential takes on a very special form. In the standard parameterization of the 2HDM scalar potential with squared mass parametersm211,m222,m212, and dimensionless couplings,λ1,λ2,??λ7, the ERPS corresponds toλ1=λ2,λ7=??λ6,m211=m222andm212=0, corresponding to a scalar potential with an enhanced generalized CP symmetry called GCP2. Many special features persist ifλ1=λ2andλ7=??λ6are retained while allowing form211??m222and/orm212??, corresponding to a scalar potential with a softly-broken GCP2 symmetry, which we designate as the ERPS4. In this paper, we examine many of the special features of the ERPS4, as well as even more specialized cases within the ERPS4 framework in which additional constraints on the scalar potential parameters are imposed. By surveying the landscape of the ERPS4, we complete the classification of 2HDM scalar potentials that exhibit an exact Higgs alignment (where the tree-level couplings of one neutral scalar coincide with those of the Standard Model Higgs boson), due to a residual symmetry that is unbroken in the vacuum. One surprising aspect of the ERPS4 is the possibility that the scalar sector is CP-conserving despite the presence of a complex parameter of the scalar potential whose complex phase cannot be removed by separate rephasings of the two scalar doublet fields. The significance of the ERPS4 regime for custodial symmetry is also discussed, and the cases where a custodial symmetric 2HDM scalar potential preserves an exact Higgs alignment are elucidated.

Recently, the MiniBooNE experiment at Fermilab has updated the results with increased data and reported an excess of560.6±119.6electron-like events (4.7?) in the neutrino operation mode. In this paper, we propose a scenario to account for the excess where a Dirac-type sterile neutrino, produced by a charged kaon decay through the neutrino mixing, decays into a leptophilic axion-like particle (??ALP) and a muon neutrino. The electron-positron pairs produced from the??ALP decays can be interpreted as electron-like events provided that their opening angle is sufficiently small. In our framework, we consider the??ALP with a massma=20MeVand an inverse decay constantce/fa=10??GeV??, allowed by the astrophysical and experimental constraints. Then, after integrating the predicted angular or visible energy spectra of the??ALP to obtain the total excess event number, we find that our scenario with sterile neutrino masses within150MeV??mN??80MeV(150MeV??mN??80MeV) and neutrino mixing parameters between10??0?�|Uμ4|2??10??(3?10???�|Uμ4|2???10??) can explain the MiniBooNE data.

In a class of neutrino mass models with modular flavor symmetries, it has been observed that CP symmetry is preserved at the fixed point (or stabilizer) of the modulus parameter?=i, whereas significant CP violation emerges within the neighbourhood of this stabilizer. In this paper, we first construct a viable model with the modularA??5symmetry, and explore the phenomenological implications for lepton masses and flavor mixing. Then, we introduce explicit perturbations to the stabilizer at?=i, and present both numerical and analytical results to understand why a small deviation from the stabilizer leads to large CP violation. As low-energy observables are very sensitive to the perturbations to model parameters, we further demonstrate that the renormalization-group running effects play an important role in confronting theoretical predictions at the high-energy scale with experimental measurements at the low-energy scale.

Axion as one of the promising dark matter candidates can be detected through narrow radio lines emitted from the magnetic white dwarf stars. Due to the existence of the strong magnetic field, the axion may resonantly convert into the radio photon (Primakoff effect) when it passes through a narrow region in the corona of the magnetic white dwarf, where the plasma frequency is equal to the axion mass. We show that for the magnetic white dwarf WD 2010+310, the future experiment SKA phase 1 with 100 hours of observation can effectively probe the parameter space of the axion-photon couplinggaγup to??10??2 GeV??for the axion mass range of0.2??.7 μeV. Note that in the low mass region (ma??.5 μeV), the WD 2010+310 could give greater sensitivity than the neutron star RX J0806.4-4123.

Neutron star (NS) as the dark matter (DM) probe has gained a broad attention recently, either from heating due to DM annihilation or its stability under the presence of DM. In this work, we investigate spin-1/2fermionic DM?charged under theU(1)Xin the dark sector. The massive gauge bosonVofU(1)Xgauge group can be produced in NS via DM annihilation. The produced gauge boson can decay into Standard Model (SM) particles before it exits NS, despite its tiny couplings to SM particles. Thus, we perform a systematic study on??¯??V??SMas a new heating mechanism for NS in addition to??¯??SMand kinetic heating from DM-baryon scattering. The self-trapping due to?Vscattering is also considered. We assume the general framework that both kinetic and mass mixing terms betweenVand SM gauge bosons are present. This allows both vector and axial-vector couplings betweenVand SM fermions even formV??mZ. Notably, the contribution from axial-vector coupling is not negligible when particles scatter relativistically. We point out that the above approaches to DM-induced NS heating are not yet adopted in recent analyses. Detectabilities of the aforementioned effects to the NS surface temperature by the future telescopes are discussed as well.