High Energy Physics - Phenomenology (hep-ph)

Abstract: We study baryogenesis via leptogenesis in an extension of the Standard Model by adding one right-handed neutrino and one triplet scalar. These heavy particles contribute to the generation of tiny neutrino mass through seesaw mechanism. The contribution of the heavy particles to the neutrino masses is inversely proportional to their corresponding masses. Considering leptogenesis is achieved by the decay of the right-handed neutrino, the new source of CP asymmetry comes solely from the decay of the right-handed neutrino with one-loop vertex diagram involving the triplet scalar. The predictiveness of the model is enhanced by introducing Fritzsch-type textures for the neutrino mass matrix and charged lepton mass matrix. We execute the parameter space study following the latest neutrino oscillation data. We study baryogenesis via leptogenesis in the two-flavoured regime, using the zero textures, and show that there is an enhancement in baryon asymmetry as compared to the unflavoured regime. For two-flavour leptogenesis we consider the suitable temperature regime $T\subset\left[10^{10},10^{11}\right]$ GeV. We also study the common correlation of CP violation between low and high-energy regimes using the geometrical description of CP violation in terms of unitarity triangle.

Abstract: We present recent progress towards a global determination of parton distribution functions (PDFs) at approximate N$^3$LO (aN$^3$LO) accuracy within the NNPDF framework. We construct a parametrisation of the $\mathcal{O}(\alpha_s^4)$ QCD splitting functions and anomalous dimensions reproducing all known exact results, estimate the associated missing and incomplete higher order uncertainties (MHOU and IHOU, respectively), and implement it in the open-source DGLAP code EKO enabling PDFs to be evolved at aN$^3$LO accuracy in the NNPDF fitting framework. We compare aN$^3$LO calculation of splitting functions with the results of lower perturbative orders and quantify the impact of the various sources of theoretical uncertainties.

Abstract: Recently, an increasing interest in UV/IR mixing phenomena has drawn attention to the range of validity of standard quantum field theory. Here we explore the consequences of such a limited range of validity in the context of radiative models for neutrino mass generation. We adopt an argument first published by Cohen, Kaplan and Nelson that gravity implies both UV and IR cutoffs, apply it to the loop integrals describing radiative corrections, and demonstrate that this effect has significant consequences for the parameter space of radiative neutrino mass models.

Abstract: We begin a series of two papers that is devoted to the study of the multi-loop effective potential evolution in $\varphi^4$-theory using the conformal symmetry. In the first part, we introduce and describe in detail the vacuum $V_{z,x}$-operation ($``V"$ stems from ``vacuum'', $\{z,x\}$ imply the corresponding coordinates) that transforms the given Green functions to the corresponding vacuum integrations which generate the effective potential. Our operation can be considered as an inverse procedure compared to the Gorishni-Isaev method. To the final goal, it is necessary to introduce also the special treatment of the mass terms as sorts of ``interaction'' in an asymptotical expansion of the generating functional.

Abstract: Based on the high statistical data of the CLAS Collaboration on $\gamma p \to \phi p$ reaction in the center-of-mass energy range of 2.2 GeV to 2.8 GeV, we investigate the possible existence of strange molecular partners of $P_c$ states, i.e., $N^*(2080)$ and $N^*(2270)$ as $K^*\Sigma$ and $K^*\Sigma^*$ molecular states.In addition to the t-channel Pomeron exchange, t-channel meson exchange including pseudo-scalar meson $(\pi,\eta)$, scalar meson $(\sigma, a_0(980), f_0(980))$, axial-vector meson $f_1(1285)$, tensor meson $f_2(1270)$, as well as s- and u-channel proton exchange, including s-channel $N^*(2080)$ and $N^*(2270)$ states can fit the data very well. The fitted coupling constants of these $N^*$ molecular states to $p\phi$ and $\gamma p$ are consistent with the results directly calculated from the relevant hadronic triangle diagrams of the molecular picture.

Abstract: We compute the complete set of two-loop master integrals for the scattering of four massless particles and a massive one. Our results are ready for phenomenological applications, removing a major obstacle to the computation of complete next-to-next-to-leading order (NNLO) QCD corrections to processes such as the production of a $H/Z/W$ boson in association with two jets at the LHC. Furthermore, they open the door to new investigations into the structure of quantum-field theories and provide precious analytic data for studying the mathematical properties of Feynman integrals.

Abstract: The lower and upper limits of the total cross section ($\sigma_{tot}$) at the projected FCC-hh have been estimated. A lower limit has been estimated using dispersion relations in combination with recent LHC data of $\sigma_{tot}$ and the $\rho$-parameter. The upper limit has been estimated using the standard $ln^{2}(s) $ evolution of $\sigma_{tot}$. Some models giving values in between those limits are also discussed.

Abstract: Searches for new physics (NP) at particle colliders typically involve multivariate analysis of kinematic distributions of final state particles produced in a decay of a hypothetical NP resonance. Since the pair-production cross-sections mediated by such resonances are strongly suppressed by the NP scale, this analysis becomes less relevant for NP searches for masses of the BSM resonance above 1 TeV. On the other hand, $t$-channel processes are less sensitive to the mass of the virtual mediator and therefore larger phase-space can be potentially probed as well as the couplings between the NP particles and the Standard Model fields. The fact that transitions between different generations of quarks and leptons may exist, the potential of the search presented in this article can be used, as a reference guide, to enlarge significantly the scope of searches performed at the LHC to flavour off-diagonal channels, in a theoretically consistent approach. In this work, we study non-resonant production of scalar leptoquarks which have been proposed in the literature to provide a potential avenue for radiative generation of neutrino masses, accommodating as well the existing flavour physics data. Final states involving just two muons at the LHC ($\mu^+, \mu^-$), are used as a well-motivated case study.

Abstract: The small field inflation (SFI) of Coleman-Weinberg (CW) type suffers from precise tuning of the initial inflaton field value to be away from the true vacuum one. We propose a dynamical trapping mechanism to solve this problem: an ultra-supercooling caused by an almost scale-invariant CW potential traps the inflaton at the false vacuum, far away from the true vacuum dominantly created by the quantum scale anomaly, and allows the inflaton to dynamically start the slow-roll down due to a classical explicit-scale breaking effect. To be concrete, we employ a successful CW-SFI model and show that the proposed mechanism works consistently with the observed bounds on the inflation parameters. The proposed new mechanism thus provides new insights for developing small field inflation models.

Abstract: Currently, flavour-cryptoexotic tetraquarks form the most common sort of all experimentally established exotic multiquark hadrons. This note points out a few promising concepts that should help improve theoretical (but, for several reasons, not quite straightforward) analyses of such kind of states: among others, their scope of application encompasses the strong interactions in the limit of (arbitrarily) large numbers of colours, and equally analytical and nonperturbative approaches to multiquark states.

Abstract: Taking into account of the mixing of Higgs-radion in the Randall-Sundrum model and the vector anomalous couplings, we investigate the production of Higgs boson or radion associated with the photon through $\gamma^{*}\gamma^{*}$ collisions at the International Linear Collider (ILC) and Large Hadron Collider (LHC). The total cross-section depends strongly on the vacuum expectation value (VEV) of the radion field $\Lambda_{\phi}$, the radion mass $m_{\phi}$, the parameters of anomalous couplings. The result shows that the total cross-section in $\gamma h$/$\gamma \phi$ production at the LHC is much larger than that at the ILC.

Abstract: In cosmological first-order phase transitions (PT) with relativistic bubble walls, high-energy shells of particles generically form on the inner and outer sides of the walls. Shells from different bubbles can then collide with energies much larger than the PT or inflation scales, and with sizeable rates, realising a `bubbletron'. As an application, we calculate the maximal dark matter mass $M_{DM}$ that can be produced from shell collisions in a U(1) gauge PT, for scales of the PT $v_\varphi$ from MeV to $10^{16}$ GeV. We find for example $M_{DM} \sim 10^6/10^{11}/10^{15}$ GeV for $v_\varphi \sim 10^{-2}/10^3/10^8$ GeV. The gravity wave signal sourced at the PT then links Pulsar Timing Arrays with the PeV scale, LISA with the ZeV one, and the Einstein Telescope with grand unification.

Abstract: We study the discovery potential of massive graviton-like spin-2 particles coupled to standard model fields, produced in photon-photon collisions at the Large Hadron Collider (LHC) as well as in electron-positron ($e^+e^-$) collisions, within an effective theory with and without universal couplings. Our focus is on a massive graviton G coupled to the electromagnetic field, which decays via $\mathrm{G}\to \gamma \gamma$ and leads to a resonant excess of diphotons over the light-by-light scattering continuum at the LHC, and of triphoton final states at $e^+e^-$ colliders. Based on similar searches performed for pseudoscalar axion-like particles (ALPs), and taking into account the different cross sections, $\gamma \gamma$ partial widths, and decay kinematics of the pseudoscalar and tensor particles, we reinterpret existing experimental bounds on the ALP-$\gamma$ coupling into G-$\gamma$ ones. Using the available data, exclusion limits on the graviton-photon coupling are set down to $g_{\mathrm{G}\gamma\gamma}\approx 1$--0.05~TeV$^{-1}$ for masses $m_\mathrm{G} \approx 100$~MeV--2~TeV. Such bounds can be improved by factors of 100 at Belle~II in the low-mass region, and of 4 at the HL-LHC at high masses, with their expected full integrated luminosities.

Abstract: We construct $ {\rm SU(3)}_{\rm L} \otimes {\rm SU(3)}_{\rm R}$ invariant parity doublet models within the linear realization of the chiral symmetry. Describing baryons as the superposition of linear representations should be useful description for transitions toward the chiral restoration. The major problem in the construction is that there are much more chiral representations for baryons than in the two-flavor cases. To reduce the number of possible baryon fields, we introduce a hierarchy between representations with good or bad diquarks (called soft and hard baryon representations, respectively). We use $(3,\bar3)+(\bar3,3)$ and $(8,1)+(1,8)$ as soft to construct a chiral invariant Lagrangian, while the $(3,6)+(6,3)$ representations are assumed to be integrated out, leaving some effective interactions. The mass splitting associated with the strange quark mass is analyzed in the first and second order in the meson fields $M$ in $(3,\bar3)+(\bar3,3)$ representations. We found that the chiral $ {\rm SU(3)}_L \otimes {\rm SU(3)}_R$ constraints are far more restrictive than the $ {\rm SU(3)}_V$ constraints used in conventional models for baryons. After extensive analyses within $(3,\bar3)+(\bar3,3)$ and $(8,1)+(1,8)$ models, we found that models in the first order of $M$ do not reproduce the mass hierarchy correctly, although the {\GO} is satisfied. In the second order, the masses of the positive parity channels are reproduced well up to the first radial excitations, while some problem in the mass ordering remains in a negative parity channel. Apparently the baryon dynamics is not well-saturated by just $(3,\bar3)+(\bar3,3)$ and $(8,1)+(1,8)$ representations, as indicated by the necessity of terms higher order in $M$.

Abstract: We study the exotic muon decays with five charged tracks in the final state. First, we investigate the Standard Model rate for $\mu^+ \to 3e^+\,2e^-\,2\nu$ ($B = 4.0\times 10^{-10})$ and find that the Mu3e experiment should have tens to hundreds of signal events per $10^{15}$ $\mu^+$ decays, depending on the signal selection strategy. We then turn to a neutrinoless $\mu^+ \to 3e^+\,2e^-$ decay that may arise in new-physics models with lepton-flavor-violating effective operators involving a dark Higgs $h_d$. Following its production in $\mu^+ \to e^+ h_d$ decays, the dark Higgs can undergo a decay cascade to two $e^+e^-$ pairs through two dark photons, $h_d \to \gamma_d \gamma_d \to 2(e^+e^-)$. We show that a $\mu^+ \to 3e^+\,2e^-$ search at the Mu3e experiment, with potential sensitivity to the branching ratio at the $O(10^{-12})$ level or below, can explore new regions of parameter space and new physics scales as high as $\Lambda \sim 10^{15}$ GeV.