High Energy Physics - Phenomenology (hep-ph)

Abstract: We revisit the Affleck-Dine leptogenesis via the $L H_u$ flat direction with a light slepton field. Although the light slepton field is favored in low-energy SUSY phenomenologies, such as the muon $g-2$ anomaly and bino-slepton coannihilation, it may cause a problem in the Affleck-Dine leptogenesis: it may create an unwanted charge-breaking vacuum in the Affleck-Dine field potential so that the Affleck-Dine field is trapped during the course of leptogenesis. We investigate the conditions under which such an unwanted vacuum exists and clarify that both thermal and quantum corrections are important for the (temporal) disappearance of the charge-breaking minimum. We also confirm that if the charge-breaking vacuum disappears due to the thermal or quantum correction, the correct baryon asymmetry can be produced while avoiding the cosmological gravitino problem.

Abstract: We introduce a dark photon considering a U(1) gauge extension of the standard model in particle physics. Provided that the extra U(1) symmetry is unbroken, the dark photon is massless and has no coupling to the standard electromagnetic current. Higher-dimensional operators describe interactions of the massless dark photon with particles in the standard model. We investigate the interactions of the massless dark photon with charged leptons via dipole operators, mainly focusing on the lepton family-violating processes. We present an improved constraint in the polarized two-body muon decay and a set of new bounds in tau decays. We also examine possible lepton family-violating signals of the massless dark photon in future lepton colliders.

Abstract: We study a novel six-dimensional gauge theory compactified on the $T^2/{\mathbb Z}_3$ orbifold utilizing the diagonal embedding method. The bulk gauge group is $G\times G\times G$, and the diagonal part $G^{\rm diag}$ remains manifest in the effective four-dimensional theory. Further spontaneous breaking of the gauge symmetry occurs through the dynamics of the zero modes of the extra-dimensional components of the gauge field. We apply this setup to the $SU(5)$ grand unified theory and examine the vacuum structure determined by the dynamics of the zero modes. The phenomenologically viable models are shown, in which the unified symmetry $G^{\rm diag}\cong SU(5)$ is spontaneously broken down to $SU(3)\times SU(2)\times U(1)$ at the global minima of the one-loop effective potential for the zero modes. This spontaneous breaking provides notable features such as a realization of the doublet-triplet splitting without fine tuning and a prediction of light adjoint fields.

Abstract: Neutrino--antineutrino ($\nu\bar\nu$) pair production is one of the main processes responsible for the energy loss of stars. Apart from the collision of two ($\gamma\gamma\to\nu\bar\nu$) or three ($\gamma\gamma\gamma\to\nu\bar\nu$) real photons, photon decay and photon collisions in the presence of nuclear Coulomb fields or external magnetic fields have been considered previously. Here, we study the low-energy photon decay into a pair of neutrino and antineutrino in the presence of a combined homogeneous magnetic field and the Coulomb field of a nucleus with charge number $Z$.

Abstract: We demonstrate that the longitudinal single target-spin asymmetry in exclusive $\pi^0$ production in $ep$ collisions can give access to the imaginary part of the gluon generalized transverse momentum distribution (GTMD) $F_{1,4}$. Such a longitudinal spin asymmetry that results from the Coulomb-nuclear interference effect, leads to a characteristic azimuthal angular correlation of $\sin 2\phi$, where $\phi$ is the azimuthal angle between the scattered lepton transverse momentum and the recoiled proton's transverse momentum. We also present a numerical estimate of the asymmetry for the kinematics accessible at EIC and EicC.

Abstract: Long-standing efforts to detect axions are driven by two compelling prospects, naturally accounting for the absence of charge-conjugation and parity symmetry breaking in quantum chromodynamics, and for the elusive dark matter at ultralight mass scale. Many experiments use the axion-photon coupling to probe the magnetic-field-mediated conversion of axions to photons. Here, we show that axion matter in a magnetic field induces electric dipole transitions in atoms and molecules. When applied to Rydberg atoms, which feature particularly large transition dipole elements, this effect promises an outstanding sensitivity for detecting ultralight dark matter. Our estimates show that it outperforms current experiments and other theoretical approaches based on axion-photon conversion by several orders of magnitude. The Rydberg atomic gases offer a flexible and inexpensive experimental platform that can operate at room temperature. We project the sensitivity by quantizing the axion-modified Maxwell equations to accurately describe atoms and molecules as quantum sensors wherever axion dark matter is present.

Abstract: We demonstrate that the Higgs boson mass can be extracted from the dispersion relation obeyed by the correlation function of two $b$-quark scalar currents. The solution to the dispersion relation with the input from the perturbative evaluation of the correlation function up to next-to-leading order in QCD and with the $b$ quark mass $m_b=4.43$ GeV demands a specific Higgs mass 115 GeV. Our observation offers an alternative resolution to the long-standing fine-tuning problem of the Standard Model (SM): the Higgs mass is determined dynamically for the internal consistency of the SM. The similar formalism, as applied to the correlation function of two $b$-quark vector currents with the same $m_b$, leads to the $Z$ boson mass 90.8 GeV. This solution exists only when the $Z$ and $W$ boson masses are proportionate, conforming to the Higgs mechanism of the electroweak symmetry breaking. We then consider the mixing between the $Q\bar u$ and $\bar Qu$ states for a fictitious heavy quark $Q$ and a $u$ quark through the $b\bar b$ channel, inspired by our earlier analysis of neutral meson mixing. Its dispersion relation, given the perturbative input from the responsible box diagrams and the same $m_b$, fixes the top quark mass 177 GeV. It is highly nontrivial to predict the above electroweak-scale masses with at most 8\% deviation from their measured values using the single parameter $m_b$. More accurate results are expected, as more precise perturbative inputs are adopted.

Abstract: We present a review on the self-resonant dark matter scenarios where multiple components of dark matter give rise to a resonant condition in the $u$-channel diagrams for their comparable masses. In this case, there is no need of lighter mediators for enhancing the self-scattering and annihilation cross sections for dark matter. We discuss the velocity-dependent self-scattering for the small-scale problems, the relic density of self-resonant dark matter, and the observable signatures in indirect and detection experiments.

Abstract: We develop a bottom-up approach to flavour models which combine modular symmetry with orbifold constructions. We first consider a 6d orbifold $\mathbb{T}^2/\mathbb{Z}_N$, with a single torus defined by one complex coordinate $z$ and a single modulus field $\tau$, playing the role of a flavon transforming under a finite modular symmetry. We then consider 10d orbifolds with three factorizable tori, each defined by one complex coordinate $z_i$ and involving the three moduli fields $\tau_1, \tau_2, \tau_3$ transforming under three finite modular groups. Assuming supersymmetry, consistent with the holomorphicity requirement, we consider all 10d orbifolds of the form $(\mathbb{T}^2)^3/(\mathbb{Z}_N\times\mathbb{Z}_M)$, and list those which have fixed values of the moduli fields (up to an integer). The key advantage of such 10d orbifold models over 4d models is that the values of the moduli are not completely free but are constrained by geometry and symmetry. To illustrate the approach we discuss a 10d modular seesaw model with $S_4^3$ modular symmetry based on $(\mathbb{T}^2)^3/(\mathbb{Z}_4\times\mathbb{Z}_2)$ where $\tau_1=i,\ \tau_2=i+2$ are constrained by the orbifold, while $\tau_3=\omega$ is determined by imposing a further remnant $S_4$ flavour symmetry, leading to a highly predictive example in the class CSD$(n)$ with $n=1-\sqrt{6}$.

Abstract: We introduce HighTEA, a new paradigm for deploying fully-differential next-to-next-to leading order (NNLO) calculations for collider observables. In principle, any infrared safe observable can be computed and, with very few restrictions, the user has complete freedom in defining their calculation's setup. For example, one can compute generic n-dimensional distributions, can define kinematic variables and factorization/renormalization scales, and can modify the strong coupling and parton distributions. HighTEA operates on the principle of analyzing precomputed events. It has all the required hardware and software infrastructure such that users only need to request their calculation via the internet before receiving the results, typically within minutes, in the form of a histogram. No specialized knowledge or computing infrastructure is required to fully utilize HighTEA, which could be used by both experts in particle physics and the general public. The current focus is on all classes of LHC processes. Extensions beyond NNLO, or to $e^+e^-$ colliders, are natural next steps.

Abstract: We introduce GRANIITTI, a new Monte Carlo event generator designed especially to solve the enigma of glueballs at the LHC. We discuss the available physics processes, compare the simulations against STAR data from RHIC and span ambitious future directions towards the first diffractive event generator with a deep learning-enhanced computational engine.