High Energy Physics - Phenomenology (hep-ph)

Abstract: Mass-dependent quark contributions are of great importance to DIS processes. The simplified-ACOT-scheme includes these effects over a wide range of momentum transfers up to next-to-leading order in QCD. In recent years an improvement in the case of neutral current DIS has been achieved by using zero-mass contributions up to next-to-next-to-leading order (NNLO) with massive phase-space constraints. In this work, we extend this approach to the case of charged current DIS and provide an implementation in the open-source code APFEL++. The increased precision will be valuable for ongoing and future neutrino programs, the Electron-Ion-Collider and the studies of partonic substructure of hadrons and nuclei. A highly efficient implementation using gridding techniques extends the applicability of the code to the determination of parton distribution functions (PDFs).

Abstract: The form factors of $B_{(s)}$ decays into P-wave excited charmed mesons (including $D^*_0(2300)$, $D_1(2430)$, $D_1(2420)$, $D^*_2(2460)$ and their strange counterparts, denoted generically as $D^{**}_{(s)}$) are systematically calculated via the QCD sum rules in the framework of heavy quark effective field theory (HQEFT). We consider contributions up to the next leading order of heavy quark expansion and give all the relevant form factors, including the scalar and tensor ones which are only related to possible new physics effects. The expressions of form factors in terms of several universal wave functions are derived via the heavy quark expansion. These universal functions can be evaluated through QCD sum rules. Then the numerical results of form factors are presented. With the form factors given here, a model independent analysis of relevant semileptonic decays $B_{(s)} \rightarrow D^{**}_{(s)} l \bar{\nu}_l$ is performed, including the contributions from possible new physics effects. Our predictions for the differential decay widths, branching fractions and the ratios of branching fractions $R(D^{**}_{(s)})$ may be tested by more precise experiments in the future.

Abstract: The discoveries of the $P_{\psi s}^\Lambda(4459)$ and $P_{\psi s}^\Lambda(4338)$ as the potential $\Xi_c\bar D^{(*)}$ molecules have sparked our curiosity in exploring a novel class of molecular $P_{\psi s}^{\Lambda/\Sigma}$ pentaquarks. In this study, we carry out an investigation into the higher molecular pentaquarks, specifically focusing on the $P_{\psi s}^{\Lambda/\Sigma}$ states arising from the $\Xi_c^{(\prime,*)}\bar D_1/\Xi_c^{(\prime,*)}\bar D_2^*$ interactions. Our approach employs the one-boson-exchange model, incorporating both the $S$-$D$ wave mixing effect and the coupled channel effect. Our numerical results suggest that the $\Xi_c\bar D_1$ states with $I(J^P)=0({1}/{2}^+,\,{3}/{2}^+)$, the $\Xi_c\bar D_2^*$ states with $I(J^P)=0({3}/{2}^+,\,{5}/{2}^+)$, the $\Xi_c^{\prime}\bar D_1$ states with $I(J^P)=0({1}/{2}^+,\,{3}/{2}^+)$, the $\Xi_c^{\prime}\bar D_2^*$ states with $I(J^P)=0({3}/{2}^+,\,{5}/{2}^+)$, the $\Xi_c^{*}\bar D_1$ states with $I(J^P)=0({1}/{2}^+,\,{3}/{2}^+,\,{5}/{2}^+)$, and the $\Xi_c^{*}\bar D_2^*$ states with $I(J^P)=0({1}/{2}^+,\,{3}/{2}^+,\,{5}/{2}^+,\,{7}/{2}^+)$ can be recommended as the most promising molecular $P_{\psi s}^\Lambda$ pentaquark candidates, and there may exist the potential molecular $P_{\psi s}^\Sigma$ pentaquark candidates for several isovector $\Xi_c^{(\prime,*)}\bar D_1/\Xi_c^{(\prime,*)}\bar D_2^*$ states. With the higher statistical data accumulation at the LHCb's Run II and Run III status, there is the possibility that our predicted $P_{\psi s}^{\Lambda/\Sigma}$ states can be detected through the weak decay of the $\Xi_b$ baryon, especially in hunting for the predicted $P_{\psi s}^\Lambda$ states.

Abstract: We simulate the space-time dynamics of high-energy collisions based on a microscopic kinetic description, in order to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number $\mathrm{Re}^{-1}$ is sufficiently small and the early pre-equilibrium stage is properly accounted for. By determining the breakdown of hydrodynamics as a function of system size and energy, we find that it is quantitatively accurate in central lead-lead collisions at LHC energies, but should not be used in typical proton-lead or proton-proton collisions, where the development of collective flow can not accurately be described within hydrodynamics.

Abstract: The axion, originally postulated by Peccei and Quinn to solve the strong CP problem, has become of great interest in particle and astroparticle phenomenology. Yet it has a problem. It is widely assumed that the axion leaves the nonperturbative features of QCD, such as the axial anomaly and chiral symmetry breaking, unscathed. This is, however, not the case. It turns out that the anomalous coupling of the axion to the gauge bosons can be integrated partially, leaving behind a path integral extending over topologically trivial gauge potentials only. This has far reaching consequences. We conclude that the Peccei-Quinn axion extension of the Standard Model is not a viable theory.

Abstract: We study the impact of axions or axion-like particles on birefringent (i.e., polarization changing) scattering of x-ray photons at the Coulomb field of nuclei superimposed by optical lasers of ultra-high intensity. Applying the specifications of the Helmholtz International Beamline for Extreme Fields (HIBEF), we find that this set-up can be more sensitive than previous experiments such as PVLAS in a large domain of parameter space. Furthermore, by changing the pump and probe laser orientations and frequencies, one can scan different axion masses.

Abstract: We study the non-strange and strangeonium light hybrid mesons with $J^{PC}=2^{+-}$ by using the method of QCD sum rules. The local hybrid interpolating currents with three Lorentz indices are constructed to couple to such exotic quantum numbers. We calculate the correlation functions up to dimension eight condensates at the leading order of $\alpha_{s}$. In our results, the masses of the non-strange $b_2$ and $h_2$ hybrids are about $2.65~\mathrm{GeV}$, while that of the strangeonium $h_2^\prime$ hybrid is about $2.74~\mathrm{GeV}$. Such exotic $2^{+-}$ hybrids can be generated through both the two-gluon and three-gluon emission processes in the radiative decays of $\chi_{cJ}$. Moreover, these hybrid mesons may be detectable due to their peculiar decay behaviors and small decay widths. Using the high-statistics data samples of $\psi(3686)$ in BESIII and BelleII, it is possible to hunt for such hybrid states through the partial wave analyses in the $b_2\to\omega/a_1/h_1/a_2\pi\to4\pi$, $h_2\to\rho\pi\to3\pi$ and $h_2\to b_1\pi\to5\pi$ processes.

Abstract: Renormalisation group analysis with the present measurements of the top quark mass $m_t = 172.69\pm 0.30$ GeV indicates that the Standard Model (SM) Higgs potential becomes unstable at energy scales $\sim 10^{10}$ GeV. This may be interpreted as hinting at new particles at high energy. The minimal extension of the SM that can avoid this instability while leaving the SM Higgs as the sole scalar particle of the theory is obtained by adding suitable fermions to the SM. These fermions are good dark matter candidates and the model is known as the minimal dark matter model. We revisit the inflationary scenario based on the minimal dark matter model, taking into account updated parameter constraints and recent understanding of reheating dynamics. We explore the model with different values of the right-handed neutrino mass and find that the cosmological prediction is insensitive to such details. We obtained a spectral index of the cosmic microwave background $n_s=9.672$ and a tensor-to-scalar ratio $r=0.0031$ as a robust prediction of this scenario.

Abstract: In this article, we study in detail the double-$J/\psi$ yield through $Z$ decay at the next-to-leading-order (NLO) QCD accuracy within the nonrelativistic QCD factorization. At the tree level, the pure QCD diagrams predict a branching ratio of $\mathcal{B}_{Z \to J/\psi+J/\psi} \sim 10^{-12}$; however, the inclusion of the QED diagrams would augment this prediction by approximately 2-3 orders of magnitude. After incorporating the QCD corrections, the QCD results exhibit a considerable increase, whereas the QED results undergo a substantial reduction. Combing the QCD and QED contributions at NLO in $\alpha_s$, it is observed that the prediction of $\mathcal{B}_{Z \to J/\psi+J/\psi}=(1.110^{+0.334+0.054}_{-0.241-0.001})\times 10^{-10}$, which displays a fairly steady dependence on the renormalization scale, is significantly lower than the upper limits released by CMS.

Abstract: We present a comprehensive study on the longitudinal flow decorrelation in heavy-ion collisions at the RHIC Beam Energy Scan (BES) energies, spanning from $\sqrt{s_{NN}}$ = 11.5 to 200 GeV in Au+Au collisions, using the A Multi-Phase Transport (AMPT) model. Our investigation entails measuring the second and third order factorization ratios ($r_{2}$ and $r_{3}$) across all these energies. We observed that the decorrelation is stronger at lower energies compared to higher collision energies, with this energy dependence trend being more prominent in $r_{3}$. Additionally, we analyze the contributions of flow-plane and flow magnitude decorrelation to the overall decorrelation phenomenon. Notably, our findings reveal that flow plane decorrelation exhibits a dominant contribution compared to flow magnitude decorrelation. Moreover, we incorporate a recently proposed observable, the four particle cumulant ($T_{2}$), which remains resilient to non-flow effects and exhibits sensitivity to different decorrelation patterns. Through the measurement of $T_{2}$, we consistently observe an S-shaped or torqued decorrelation across all energy ranges.

Abstract: The properties of fully-heavy arrangements including a number of quarks between 5 and 12 were calculated within the framework of a constituent quark model by using a diffusion Monte Carlo technique. We considered only clusters in which all the quarks had the same mass, and whose number of particles and antiparticles were adequate to produce color singlets. All the multiquarks were in their lowest possible values of $L^2$ and $S^2$ operators. This means that we considered only color-spin wavefunctions that were antisymmetric with respect to the interchange of {\em any} two quarks of the same type. We found that in both all-$c$ and all-$b$ multiquarks, the mass per particle levels off for arrangements with a number of quarks larger of equal than six. The analysis of their structure implies that the fully-heavy multiquarks are compact structures.

Abstract: While experimental studies on jet quenching have achieved a large sophistication, the theoretical description of this phenomenon still misses some important points. One of them is the interplay of vacuum-like emissions, usually formulated in momentum space, with the medium induced ones that demand an interplay with a space-time picture of the medium and thus must be formulated in position space. A unified description of both vacuum and medium-induced emissions is lacking. In this work, we compute the tree-level probability of a double gluon emission in vacuum, and identify the enhanced phase-space regions for each diagram, corresponding to different configurations of the parton cascade. This calculation provides a parametric form for the formation times associated with each diagram, highlighting the equivalence of various ordering variables at double logarithmic accuracy. This equivalence is further explored by building a toy Monte-Carlo parton shower ordered in formation time, virtuality, transverse momentum, and angle. Aiming at a link with jet substructure, we compute the Lund Plane distributions and trajectories for each ordering prescription. We also compute the distributions in number of splittings and final partons, with the goal of clarifying the differences to be expected from the different ordering variables and the vetoes that must be implemented at Monte Carlo level to conserve energy-momentum, which turn out to have a sizeable influence on the shower's evolution.

Abstract: About 40 years ago, the neutrino was ruled out as the dark matter particle based on several arguments. Here I use the well-established concept of quantum uncertainties of position and momentum to describe the decoupling of neutrinos from the primordial plasma, which took place about half a second after the Big Bang. In this way I show that the main arguments against the neutrino are either wrong or have loopholes, and conclude that the neutrino urgently needs to be reconsidered, not as a 'hot', but as the 'cold' dark matter particle.

Abstract: We discuss the recent progress that has been made towards the computation of three-loop non-planar master integrals relevant to next-to-next-to-next-to-leading-order (N$^3$LO) corrections to processes such as H+jet production at the LHC. We describe the analytic structure of these integrals, as well as several technical issues regarding their analytic computation using canonical differential equations. Finally, we comment on the remaining steps towards the computation of all relevant three-loop topologies and their application to amplitude calculations.

Abstract: With the emersion of precise cosmology and the emergence of cosmic tensions, we are faced with the question of whether the simple model of cold dark matter needs to be extended and whether doing so can alleviate the tensions and improve our understanding of the properties of dark matter. In this study, we investigate one of the generalized models of dark matter so that the behavior of this dark matter changes according to the scale of $k$. In large scales (small $k$'s), the dark matter is cold, while it becomes warm for small scales (large $k$'s). This behavior is modeled phenomenologically for two different scenarios. We show that the $S_8$ tension can be alleviated, but the $H_0$ tension becomes milder while not too much.

Abstract: As is well-known, Trinification, \ie, the extension of the Standard Model (SM) to $[SU(3)]^3=SU(3)_c\times SU(3)_L\times SU(3)_R$ as occurs in $E_6$ models, allows for a partial unification of the gauge forces even though quarks and leptons remain in separate multiplets so that no heavy gauge or scalar fields exist which can generate proton decay. The extension of this idea to Quartification, by including an additional $SU(3)'$ factor, has also been considered in the literature maintaining the basic attributes of Trinification but now allowing, \eg, for a more symmetric treatment of quarks and leptons at the price of new matter fields and gauge interactions. In this paper, we will consider this $SU(3)'$ to be the `dark' gauge group, now containing the familiar $U(1)_D$ subgroup, under which the SM fields are all neutral, which is associated with kinetic mixing (KM) and the existence of a light, $\lsim 1 $ GeV dark photon. This setup naturally predicts the existence of color-singlet portal matter (PM) fields, carrying both electromagnetic and $U(1)_D$ dark charges, that are necessary to generate this KM at the 1-loop level and whose masses are directly tied with those of the many new gauge bosons that originate from the extended gauge sector. In this paper, after a discussion of the detailed structure of this model, we present a broad survey of the collider phenomenology of the large set of new fields that must necessarily arise from this setup in a simplified version involving only a single generation of fermions. We demonstrate that several new signatures may be anticipated at the LHC as well as at future hadron and lepton colliders if such models are realized in nature.

Abstract: In recent years, the importance of the electronic in-medium effect in the sub-GeV dark matter (DM) direct detection has been recognized and a coherent formulation of the DM-electron scattering based the linear response theory has been well established in the literature. In this paper, we apply the formulation to the scattering between DM particles and solar medium, and it is found that the dynamic structure factor inherently incorporate the particle-particle scattering and in-medium effect. Using this tool and taking a benchmark model as an example, we demonstrate how the in-medium effect affect the scattering of DM particles in the Sun, in both the heavy and light mediator limit. Formulae derived in this work lay the foundation for accurately calculating the spectra of solar-accelerated DM particles, which is of particular importance for the detection of DM particles via plasmon in semiconductor targets.

Abstract: Axions and axion-like particles (ALPs) are ubiquitous in popular attempts to solve supercalifragilisticexpialidocious puzzles of Nature. A widespread and vivid experimental programme spanning a vast range of mass scales and decades of couplings strives to find evidence for these elusive but theoretically well-motivated particles. In the absence of clear guiding principle, effective field theories (EFTs) prove to be an efficient tool in this experimental quest. Hilbert series technologies are a privileged instrument of the EFT toolbox to enumerate and classify operators. In this work, we compute explicitly the Hilbert series capturing the interactions of a generic ALP to the Standard Model particles above and below the electroweak symmetry scale, which allow us to build bases of operators up to dimension-8. In particular, we revealed a remarkable structure of the Hilbert series that isolates the shift-symmetry breaking and preserving interactions. Furthermore, we provide an ancillary file of the Hilbert series up to dimension 15 to supplement our findings, which can be used for further analysis and exploration.

Abstract: We investigate detection possibility of light dark photon in the forward experiments at the LHC, such as the SND@LHC and the FASER experiments. We assume that the dark photon mass is smaller than twice of the electron mass. Then the dark photon is long-lived and copiously produced through a neutral pion decay. Such dark photons would easily pass through 100 m of rock in front of the forward experiments and the detector targets, but some portion of them could be converted into an electron-positron pair inside the detector leaving an isolated electromagnetic shower as a new physics signature of the dark photon. Our estimation shows that in the range of kinetic mixing parameter $4\times10^{-5} \lesssim \epsilon \lesssim 2\times10^{-1}$, more than 10 signal events of the dark photon can be produced assuming 150 fb$^{-1}$ integrated luminosity.

Abstract: We analyse the cross-section of events with Large Rapidity Gaps observed in proton-lead collisions by the CMS collaboration. The role of the transverse size of elementary $pN$ amplitude is discussed. We emphasize that the cross-section of incoming proton dissociation caused by the photon radiated off the lead ion is close to the value of $d\sigma/d\Delta\eta^F$ measured by the CMS, and it is not clear why there is no room in the data for the Pomeron-induced contribution

Abstract: We investigate the observed muon deficit in air shower simulations when compared to ultrahigh-energy cosmic ray (UHECR) data. Gleaned from the observed enhancement of strangeness production in ALICE data, the associated $\pi \leftrightarrow K$ swap is taken as a cornerstone to resolve the muon puzzle via its corresponding impact on the shower evolution. We develop a phenomenological model in terms of the $\pi \leftrightarrow K$ swapping probability $F_s$. We provide a parametrization of $F_s (E^{\rm (proj)}, \eta)$ that can accommodate the UHECR data, where $E^{\rm (proj)}$ is the projectile energy and $\eta$ the pseudorapidity. We also explore a future game plan for model improvement using the colossal amount of data to be collected by LHC neutrino detectors at the Forward Physics Facility (FPF). We calculate the corresponding sensitivity to $F_s$ and show that the FPF experiments will be able to probe the model phase space.