High Energy Physics - Phenomenology (hep-ph)

Abstract: We investigate the order of the QCD chiral transition in the limit of vanishing bare up/down quark masses and variations of the bare strange quark mass $0 \le m_{\mathrm{s}} \le \infty$. In this limit and due to universality long range correlations with the quantum numbers of pseudoscalar and scalar mesons may dominate the physics. In order to study the interplay between the microscopic quark and gluon degrees of freedom and the long range correlations we extend a combination of lattice Yang--Mills theory and a (truncated) version of Dyson--Schwinger equations by also taking back-reactions of mesonic degrees of freedom into account. Both this system and the meson backcoupling approach have been studied extensively in the past but this is the first work in a full $(2 + 1)$-flavor setup. Starting from the physical point, we determine the chiral susceptibilities for decreasing up/down quark masses and find good agreement with both lattice and functional renormalization group results. We then proceed to determine the order of the chiral transition along the left hand side of the Columbia plot, for chemical potentials in the range $-(30 \,\textrm{MeV})^2 \le \mu_q^2 \le (30 \,\textrm{MeV})^2$. We find a second-order phase transition throughout and no trace of a first-order region in the $N_{f} = 3$ corner of the Columbia plot. This result remains unchanged when an additional Goldstone boson due to a restored axial $\mathrm{U_A}(1)$ is taken into account.

Abstract: There are three types of fragmentation functions (FFs) which are used to describe the twist-3 cross sections of the hard semi-inclusive processes under QCD collinear factorization, and they are called intrinsic, kinematical, and dynamical FFs. In this work, we investigate the theoretical relations among these FFs for a tensor-polarized spin-1 hadron. Three Lorentz-invariance relations (LIRs) are derived by using the identities between the nonlocal quark-quark and quark-gluon-quark operators, which guarantee the frame independence of the twist-3 spin observables. The QCD equation of motion (e.o.m.) relations are also presented for the tensor-polarized FFs. In addition, we also show that the intrinsic and kinematical twist-3 FFs can be decomposed into the contributions of twist-2 FFs and twist-3 three-parton FFs, and the latter are also called dynamical FFs. If one neglects the dynamical FFs, we can obtain relations which are analogous to the Wandzura-Wilczek (WW) relation. Then, the intrinsic and kinematical twist-3 FFs are expressed in terms of the leading-twist ones. Since the FFs of a spin-1 hadron can be measured at various experimental facilities in the near future, these theoretical relations will play an important role in the analysis of the collinear tensor-polarized FFs.

Abstract: We have investigated the boson sector in an extended standard model (SM) with additional $U(1)_D$ symmetry. In the proposed model, the singlet scalar and doublet scalar Higgs are added in addition to the SM-like scalar Higgs. These scalars are also coupled to the gauge boson fields. In this work, we calculate the masses of both gauge and scalar Higgs bosons. Their masses are obtained through spontaneous symmetry breaking using the Higgs fields with non-zero vacuum expectation values. We also study numerically the positivity conditions of the vacuum expectation value of the scalars. In particular, we perform scanning of the parameter space of the potential and study the obtained scalar mass dependence on the parameter of the model.

Abstract: The axion is a hypothetical elementary particle that could solve the long-standing strong CP problem in particle physics and the dark matter mystery in the cosmos. Due to the stimulation of the ambient photons, the axion dark matter decay into photons is significantly enhanced so that its echo signal could be detected by terrestrial telescopes. As a pathfinder, we study the expected sensitivity of searching for the axion dark matter in the mass range between $0.41$ and $1.6\mu\text{eV}$ with the 21 CentiMeter Array (21CMA). We aim to cover the whole 21CMA frequency range in two years by using a 1MW emitter. We find that the resulting sensitivity on the axion-photon coupling could surpass other existing limits by about one order of magnitude.

Abstract: A recently published method for solving the neutrino evolution equation with constant matter density is further refined and used to lay out a fast and accurate algorithm for computing transition and survival probabilities. In particular, the three examples of $\overline{\nu}_e$ survival, $\overline{\nu}_\mu$ survival and $\overline{\nu}_e$ appearance probabilities are written in terms of mixing angles, mass differences and matter electron density. A program based on this new method is found to be roughly twice as fast as, and in agreement with, the leading GLoBES package. Furthermore, the behaviour of all relevant effective parameters is sketched out in terms of a range of neutrino energies, or matter electron densities. For instance, the $\overline{\nu}_e$ survival probability in constant matter density is found to have no dependence on the mixing angle $\theta_{23}$ or the CP-violating phase $\delta_{13}$.

Abstract: We systematically study and classify scotogenic models with a local U(1) gauge symmetry. These models give rise to radiative neutrino masses and a stable dark matter candidate, but avoid the theoretical problems of global and discrete symmetries. We restrict the dark sector particle content to up to four scalar or fermionic SU(2) singlets, doublets or triplets and use theoretical arguments based on anomaly freedom, Lorentz and gauge symmetry to find all possible charge assignments of these particles. The U(1) symmetry can be broken by a new Higgs boson to a residual discrete symmetry, that still stabilizes the dark matter candidate. We list the particle content and charge assignments of all non-equivalent models. Specific examples in our class of models that have been studied previously in the literature are the U(1)$_D$ scotogenic and singlet-triplet scalar models breaking to $Z_2$. We also briefly discuss the new phenomenological aspects of our model arising from the presence of a new massless dark photon or massive $Z'$ boson as well as the additional Higgs boson.

Abstract: We introduce a class of new inflation models within the waterfall region of a generalized hybrid inflation framework. The initial conditions are generated in the valley of hybrid preinflation. Both single-field and multi-field inflationary scenarios have been identified within this context. A supersymmetric realization of this scenario can successfully be achieved within the tribrid inflation framework. To assess the model's viability, we calculate the predictions of inflationary observables using the $\delta N$ formalism, demonstrating excellent agreement with the most recent Planck data. Furthermore, this model facilitates successful reheating and nonthermal leptogenesis, with the matter-field component of the inflaton identified as a sneutrino.

Abstract: We explore a dynamical mechanism to realize the emergence of a global $U(1)_{\rm PQ}$ symmetry and its spontaneous breaking at an intermediate scale for an axion solution to the strong CP problem. Such a dynamics is provided by a new supersymmetric QCD near the middle of conformal window that couples to fields spontaneously breaking the $U(1)_{\rm PQ}$ symmetry. A large anomalous dimension of the $U(1)_{\rm PQ}$ breaking fields leads to the suppression of explicit $U(1)_{\rm PQ}$-violating higher dimensional operators. The $U(1)_{\rm PQ}$ breaking vacuum is generated at a scale hierarchically smaller than the Planck scale by a non-perturbative effect. The $U(1)_{\rm PQ}$ breaking drives the conformal breaking, and all the new quarks become massive. The axion potential is generated by the ordinary color $SU(3)_C$ effect as the $U(1)_{\rm PQ}$ symmetry is only anomalous under the $SU(3)_C$. The saxion direction is stabilized by supersymmetry breaking and cosmologically harmless.

Abstract: In this work, we construct the chiral Lagrangian for a light spin-1 boson $X$ possessing both vectorial and axial couplings to the light Standard Model quarks $u, d, s$. We then use it in order to describe the tree-level, model-independent contributions to the $\Delta S = 1$ transition $K^\pm \rightarrow \pi^\pm X$, which is induced by Standard Model charged currents and is possibly enhanced by the emission of a longitudinally polarized $X$ boson. Such a flavour observable is then shown to set the best model-independent bounds on the diagonal axial couplings of $X$ to light quarks in the mass range allowed by the decay kinematics, improving the currently available constraints from beam-dump experiments and collider searches.

Abstract: Collective modes within a hot Quantum Chromodynamics (QCD) medium are obtained from the polarization tensor, considering both constant and time-varying electromagnetic fields. In both scenarios, five complex modes emerge, reliant on the wave vector ($k$), with electrical conductivity exerting significant influence. The impact of the modes on the energy loss of heavy quarks in the hot QCD medium with a background electromagnetic field has been studied by obtaining the induced electric field in terms of the polarization tensor while invoking Wong's equations. The findings are seen to be consistent with analogous approaches, reinforcing the significance of the results.