High Energy Physics - Phenomenology (hep-ph)

Abstract: In this work, the strong form factors and coupling constants of the vertices $DDJ/\psi$, $DD^{*}J/\psi$, $D^{*}D^{*}J/\psi$, $DD^{*}\eta_{c}$, $D^{*}D^{*}\eta_{c}$ are calculated within the framework of the QCD sum rule. For each vertex, we analyze the form factor considering all possible off-shell cases and the contributions of the vacuum condensate terms $\langle\overline{q}q\rangle$, $\langle\overline{q}g_{s}\sigma Gq\rangle$, $\langle g_{s}^{2}G^{2}\rangle$, $\langle f^{3}G^{3}\rangle$ and $\langle\overline{q}q\rangle\langle g_{s}^{2}G^{2}\rangle$. Then, the form factors are fitted into analytical functions $g(Q^2)$ and are extrapolated into time-like regions to get the strong coupling constants. Finally, the strong coupling constants are obtained by using on-shell cases of the intermediate mesons($Q^2=-m^2$). The results are as follows, $g_{DDJ/\psi}=5.33^{+0.57}_{-0.45}$, $g_{DD^{*}J/\psi}=4.02^{+0.36}_{-0.24}$GeV$^{-1}$, $g_{D^{*}D^{*}J/\psi}=5.98^{+0.61}_{-0.58}$, $g_{DD^{*}\eta_{c}}=4.05^{+0.42}_{-0.13}$ and $g_{D^{*}D^{*}\eta_{c}}=5.73^{+0.49}_{-0.47}$GeV$^{-1}$.

Abstract: The electroweak sphaleron process breaks the baryon number conservation within the realms of the Standard Model of particle physics (SM). Recently, it is pointed out that its decoupling may provide the out-of-equilibrium condition required for baryogenesis. In this paper, we study such a scenario taking into account the baryon-number wash-out effect of the sphaleron itself to improve the estimate. We clarify the amount of CP violation required for this scenario to explain the observed asymmetry.

Abstract: We discuss sensitivities to lepton flavor violating (and conserving) interactions at future muon colliders, especially at $\mu^+\mu^+$ colliders. Compared with the searches for rare decays of $\mu$ and $\tau$, we find that the TeV-scale future colliders have better sensitivities depending on the pattern of hierarchy in the flavor mixings. As an example, we study the case with the type-II seesaw model, where the flavor mixing parameters have direct relation to the neutrino mass matrix. At a $\mu^+ \mu^+$ collider, the number of events of the $\mu^+ \mu^+ \to \mu^+ \tau^+$ process can be larger than $\mathcal{O}(100)$ with the center of mass energy $\sqrt s = 2$ TeV, and with an integrated luminosity ${\cal L} = 1$ ab$^{-1}$, while satisfying bounds from rare decays of $\mu$ and $\tau$. We discuss impacts of the overall mass scale of neutrinos as well as CP violating phases to the number of expected events.

Abstract: We discuss the mechanism to produce electron-specific dark matter mediators of spin-0 and spin-2 in the electron fixed target experiments such as NA64 and LDMX. The positrons produced by the electromagnetic shower can produce the regarding mediators via annihilation on atomic electrons. That mechanism, for some selected kinematics, results in the enhanced sensitivity with respect to the bounds derived by the bremsstrahlung-like emission of the mediator in the specific parameter space. We derive the regarding experimental reach of the NA64 and LDMX.

Abstract: We present an efficient algorithm for constructing all the matrix elements of covariant tensor currents of massless particles of arbitrary spins in the covariant formulation. This algorithm enables us to construct all the covariant three-point vertices simply by assembling the basic building blocks, leading to the construction of the matrix elements. We revisit the closely-related two restrictions on massless particles called the Landau-Yang (LY) and Weinberg-Witten (WW) theorems for the massless particles of arbitrary spins. We find the covariance conditions on form factors causing the corresponding tensor currents to be covariant and verify that the continuity assumption of matrix elements taken in the original paper discussing the WW theorem is correct at least in the quantum field theory including conventional massless fields. By invoking a simple example, we show that in general the matrix elements given in the covariant formulation cannot cover all the covariant tensor currents fully.

Abstract: In this work, we tentatively assign the $Y(4500)$ as the $[uc]_{\tilde{A}}[\overline{uc}]_{V}+[uc]_{V}[\overline{uc}]_{\tilde{A}}+[dc]_{\tilde{A}}[\overline{dc}]_{V} +[dc]_{V}[\overline{dc}]_{\tilde{A}}$ tetraquark state with the quantum numbers $J^{PC}=1^{--}$, and study the three-body strong decay $Y(4500)\to D^{*-}D^{*0}\pi^+$ with the light-cone QCD sum rules. It is the first time to use the light-cone QCD sum rules to calculate the four-hadron coupling constants, the approach can be extended to study other three-body strong decays directly and diagnose the $X$, $Y$ and $Z$ states.

Abstract: We propose a method to explore the flavor structure of quarks and leptons with reinforcement learning. As a concrete model, we utilize a basic policy-based algorithm for models with $U(1)$ flavor symmetry. By training neural networks on the $U(1)$ charges of quarks and leptons, the agent finds 21 models to be consistent with experimentally measured masses and mixing angles of quarks and leptons. In particular, an intrinsic value of normal ordering tends to be larger than that of inverted ordering, and the normal ordering is well fitted with the current experimental data in contrast to the inverted ordering. A specific value of effective mass for the neutrinoless double beta decay and a sizable leptonic CP violation induced by an angular component of flavon field are predicted by autonomous behavior of the agent.

Abstract: We evaluate the collisional energy loss of a energetic fermion with mass $M$ propagating through a hot QED plasma with temperature $T$, including mass corrections, that is, keeping the mass $m$ of the fermion constituents of the plasma, assuming $m \ll T \ll M$. We use the bare theory to compute the contribution of hard momentum transfer collisions, and the Braaten-Pisarski resummed theory, amended with small mass corrections, for the contribution of low momentum transfer collisions, and compute the mass corrections at leading logarithmic accuracy in the regime where the energy of the heavy fermion obeys $E \ll M^2/T$. We use dimensional regularization to regulate all possible divergences in the computation. If the fermion mass is of order of the soft scale $eT$, where $e$ is the gauge coupling constant, the mass corrections are of the same order as pure perturbative corrections, while they can be substantial for larger values of $m$. We also evaluate the impact of this correction for a QCD plasma.

Abstract: The relation between the gluon density in a hadron and entanglement entropy can shed a new light on the high energy scattering behavior of hadrons: The growth above the classical geometric cross section is directly related to the increase of the internal quantum entropy from the entangled parton distribution in hadrons. A rather consistent picture emerges from the scale dependence of the Pomeron from the QCD evolution of the gluon distribution function $g(x, \mu)$, the rising of the integrated cross section in photoproduction of vector mesons, hadron multiplicity and entropy.

Abstract: We scrutinize the physical viability of the minimal non-supersymmetric $\mathrm{SO}(10)$ GUT with the scalar sector $\mathbf{45}\oplus\mathbf{126}\oplus\mathbf{10}_{\mathbb{C}}$, in which the unified symmetry is broken by the former two representations, and a realistic Yukawa sector is supported by the last two. Alongside the known issue of a relatively low GUT scale (and thus overly fast proton decay) encountered in minimally fine-tuned scenarios, we identify a very general problem of the model: the inability to properly accommodate a Standard-Model-like low-energy Higgs doublet in the perturbative regime.

Abstract: Deep Neural Networks (DNNs) are a powerful and flexible tool for information extraction and modeling. In this study, we use DNNs to extract the Sivers functions by globally fitting Semi- Inclusive Deep Inelastic Scattering (SIDIS) and Drell-Yan (DY) data. To make predictions of this Transverse Momentum-dependent Distribution (TMD), we construct a minimally biased model using data from COMPASS and HERMES. The resulting Sivers function model, constructed using SIDIS data, is also used to make predictions for DY kinematics specific to the valence and sea quarks, with careful consideration given to experimental errors, data sparsity, and complexity of phase space.

Abstract: Intersection numbers are rational scalar products among functions that admit suitable integral representations, such as Feynman integrals. Using these scalar products, the decomposition of Feynman integrals into a basis of linearly independent master integrals is reduced to a projection. We present a new method for computing intersection numbers that only uses rational operations and does not require any integral transformation or change of basis. We achieve this by systematically employing the polynomial series expansion, namely the expansion of functions in powers of a polynomial. We also introduce a new prescription for choosing dual integrals, de facto removing the explicit dependence on additional analytic regulators in the computation of intersection numbers. We describe a proof-of-concept implementation of the algorithm over finite fields and its application to the decomposition of Feynman integrals at one and two loops.