High Energy Physics - Phenomenology (hep-ph)

Abstract: In this work, we study the role of triangle singularity in the $J/\psi \to \gamma \bar{p} \Delta$ decay. We find that through a triangle mechanism, involving a triangle loop composed by $\omega$, $\pi$ and $p$, this decay may develop a triangle singularity and produce a visible peak in the invariant mass $M_{\gamma\Delta}$ around 1.73 GeV with a width of 0.02 GeV. Such a triangle mechanism may also cause significant spin effects on the final $\Delta$, which can be detected by measuring its spin density matrix elements. Our calculations show that the branching ratios due to the triangle mechanism is Br($J/\psi\to \gamma \bar p\Delta,\Delta\to \pi p$)=$1.058\times 10^{-6}$. Hopefully, this reaction can be investigated at BESIII and future experiments, e.g. Super Tau-Charm Facility, and the narrow width of the induced structure, the moving TS position and the distinct features of the spin density matrix elements of the $\Delta$ may serve as signals for the triangle singularity mechanism.

Abstract: We review the modular flavor symmetric models of quarks and leptons focusing on our works. We present some flavor models of quarks and leptons by using finite modular groups and discuss the phenomenological implications. The modular flavor symmetry gives interesting phenomena at the fixed point of modulus. As a representative, we show the successful texture structure at the fixed point $\tau = \omega$. We also study CP violation, which occurs through the modulus stabilization. Finally, we study SMEFT with modular flavor symmetry by including higher dimensional operators.

Abstract: To unify the standard model of particle physics and general relativity, we may require a quantum description of gravity, which will change our notion of spacetime at very high energies. In this dissertation we explore possible traces of new physics beyond special relativity, using the propagation of high energy astroparticles. For this purpose, the two ways of going beyond Lorentz invariance are presented, a breaking of the Lorentz invariance (Lorentz invariance violation or LIV or its deformation (doubly special relativity or DSR), emphasizing their conceptual and phenomenological differences. For the study of LIV, the work focuses on the prediction of modifications in the expected neutrino flux on Earth, both from astrophysical and cosmogenic origin (from the interaction of cosmic rays with the background radiation during their propagation). For the study of DSR we focus instead on the search for anomalies in the time of flight of massless particles (time delays) and on the study of the expected flux of gamma rays on Earth. The results obtained show the possibility of using astroparticle observations as a window to quantum gravity phenomenology, at energies attainable at present and/or in the very near future.

Abstract: Using the result of the VES Collaboration for $Br(J/\psi\to\gamma f_0(1710))$, we estimate the absolute branching fractions for the $f_0(1710)$ decays into $\pi\pi$, $K\bar K$, $\eta\eta$, $\eta\eta' $, $\omega\omega$, and $\omega\phi$. In addition, we estimate $Br(\psi(2S)\to\gamma f_0(1710))\approx3.5\times10^{-5}$ and $Br(\Upsilon(1S)\to\gamma f_0(1710))\approx1\times10^{-5}$.

Abstract: New Early Dark Energy introduces a new phase of dark energy that decays in a fast-triggered phase transition around matter-radiation equality. The presence of a trigger mechanism sets it apart from other early dark energy models. Here, we will argue that New Early Dark Energy offers a simple and natural framework to extend $\Lambda$CDM while also providing a pathway to resolving the $H_0$ tension alongside its smaller cousin, the $S_8$ tension. At the microscopic level, we discuss the possibility that the trigger is either given by an ultralight scalar field or a dark sector temperature. In both cases, it prompts the transition of an $\mathrm{eV}$-mass scalar field from its false to its true minimum. Furthermore, we argue that the same phase transition could give rise to a dynamic process for generating neutrino masses.

Abstract: Supernova neutrino boosted dark matter (SN$\nu$ BDM) and its afterglow effect have been shown to be a promising signature for beyond Standard Model (bSM) physics. The time-evolution feature of SN$\nu$ BDM allows for possibly direct inference of DM mass $m_\chi$, and results in significant background suppression with improving sensitivity. This paper extends the earlier study and provides a general framework for computing the SN$\nu$ BDM fluxes for a supernova that occurs at any location in our galaxy. A bSM $U(1)_{L_\mu-L_\tau}$ model with its gauge boson coupling to both DM and the second and third generation of leptons is considered, which allows for both DM-$\nu$ and DM-$e$ interactions. Detailed analysis of the temporal profile, angular distribution, and energy spectrum of the SN$\nu$ BDM are performed. Unique signatures in SN$\nu$ BDM allowing extraction of $m_\chi$ and detail features that contain information of the underlying interaction type are discussed. Expected sensitivities on the above new physics model from Super-Kamiokande, Hyper-Kamiokande, and DUNE detections of BDM events induced by the next galactic SN are derived and compared with the existing bounds.

Abstract: Anomalous contributions to the electric and magnetic dipole moments of the $\tau$ lepton from new physics scenarios have brought renewed interest in the development of new charge-parity violating signatures in $\tau$ pair production at Belle II energies, and also at higher energies of the Large Hadron Collider and the Future Circular Collider. In this paper, we discuss the effects of spin correlations, including transverse degrees of freedom, in the $\tau$ pair production and decay. These studies include calculating analytical formulas, obtaining numerical results, and building semi-realistic observables sensitive to the transverse spin correlations induced by the dipole moments of the $\tau$ lepton. The effects of such anomalous contributions to the dipole moments are introduced on top of precision simulations of $e^-e^+ \to \tau^-\tau^+$, $q\bar{q} \to \tau^-\tau^+$ and $\gamma\gamma \to \tau^-\tau^+$ processes, involving multi-body final states. Respective extensions of the Standard Model amplitudes and the reweighting algorithms are implemented into the {\tt KKMC} Monte Carlo, which is used to simulate $\tau$ pair production in $e^-e^+$ collisions, and the {\tt TauSpinner} program, which is used to reweight events with $\tau$ pair produced in $pp$ collisions.

Abstract: We investigate neutrino non-radiative two-body decay in vacuum, in relation to SN1987A. In a full $3\nu$ decay framework, we perform a detailed likelihood analysis of the 24 neutrino events from SN1987A observed by Kamiokande-II, IMB, and Baksan. We consider both normal and inverted neutrino mass orderings, and the possibility of strongly hierarchical and quasi-degenerate neutrino mass patterns. The results of the likelihood analysis show that the sensitivity is too low to derive bounds in the case of normal mass ordering. On the contrary, in the case of inverted mass ordering we obtain the bound $\tau/m \ge 2.4 \times 10^{5}$ s/eV ($1.2 \times 10^{5}$) s/eV at 68 $\%$ (90 $\%$) CL on the lifetime-to-mass ratio of the mass eigenstates $\nu_2$ and $\nu_1$.

Abstract: The di-leptons and di-neutrinos observed in the final states of flavor-changing neutral b decays provide an ideal platform for probing physics beyond the standard model. Although the latest measurements of $R_{K^{(*)}}$ agree well with the standard model prediction, there exists several other observables such as $P_5^{\prime}$, $\mathcal{B}(B_s\to \phi \mu^{+}\mu^{-})$ and $\mathcal{B}(B_s\to \mu^{+}\mu^{-})$ in $b\to s \ell\ell$ transition decays that shows deviation from the standard model prediction. Similalry, very recently Belle II collaboration reported a more precise upper bound of $\mathcal{B}(B\to K^+\nu\bar{\nu}) < 4.1\times 10^{-5}$ by employing a new inclusive tagging approach and it also deviates from the standard model expectation. The $b\to s l^{+}l^{-}$ and $b\to s\nu\bar{\nu}$ transition decays are related not only in the standard model but also in beyond the standard model physics due to $SU(2)_L$ gauge symmetry, and can be most effectively investigated using the standard model effective field theory formalism. Additionally, the $b\to s\nu\bar{\nu}$ decay channels are theoretically cleaner than the corresponding $b\to s l^{+}l^{-}$ decays, as these processes do not get contributions from non-factorizable corrections and photonic penguin contributions. In this context, we study $\Lambda_b\to (\Lambda^*(\to pK^-), \Lambda(\to p\pi))({\mu}^{+}\mu^{-},\,\nu\bar{\nu})$ baryonic decays undergoing $b\to s \ell^{+}\ell^{-}$ and $b\to s\nu\bar{\nu}$ quark level transitions in a standard model effective field theory formalism. We give predictions of several observables pertaining to these decay channels in the standard model and in case of several new physics scenarios.

Abstract: Mesons with heavy flavor content are an exceptional probe of the hot QCD medium produced in heavy-ion collisions. In the past few years, significant progress has been made toward describing the modification of the properties of heavy mesons in the hadronic phase at finite temperature. Ground-state and excited-state thermal spectral properties can be computed within a self-consistent many-body approach that employs appropriate hadron-hadron effective interactions, providing a unique opportunity to confront hadronic Effective Field Theory predictions with recent and forthcoming lattice QCD simulations and experimental data. In this article, we revisit the application of the imaginary-time formalism to extend the calculation of unitarized scattering amplitudes from the vacuum to finite temperature. These methods allow us to obtain the ground-state thermal spectral functions. The thermal properties of the excited states that are dynamically generated within the molecular picture are also directly accessible. We present here the results of this approach for the open-charm and open-bottom sectors. We also analyze how the heavy-flavor transport properties, which are strongly correlated to experimental observables in heavy-ion collisions, are modified in hot matter. In particular, transport coefficients can be computed using an off-shell kinetic theory that is fully consistent with the effective theory describing the scattering processes. The results of this procedure for both charm and bottom transport coefficients are briefly discussed.

Abstract: We discuss a class of theories for Majorana neutrinos where the total lepton number is a local gauge symmetry. These theories predict a dark matter candidate from anomaly cancellation. We discuss the properties of the dark matter candidate and using the cosmological bounds, we obtain the upper bound on the lepton number symmetry breaking scale. The dark matter candidate has unique annihilation channels due to the fact that the theory predicts a light pseudo-Goldstone boson, the Majoron, and one can obtain the correct relic density in a large fraction of the parameter space. In this context, the seesaw scale is below the ${\cal{O}}(10^2)$TeV scale and one can hope to test the origin of neutrino masses at current or future colliders. We discuss the lepton number violating Higgs decays and the possibility to observe lepton number violation at the Large Hadron Collider.

Abstract: The properties of the pion quasiparticle in hot and dense isospin medium, including the temperature and isospin chemical potential dependence of their screening mass, pole mass and thermal width, as well as their relationships with the pion superfluid phase transition, are investigated in the framework of two-flavor ($N_{f}=2$) soft-wall AdS/QCD models. We extract the screening mass of the pion from the pole of the spatial two-point Retarded correlation function. We find that the screening masses of both neutral and charged pions increase monotonously with the increasing of temperature. However, the isospin chemical potential $\mu_{I}$ would depress the screening masses of the charged pions, $m_{\pi^{\pm},\rm{scr}}$. With the increasing of $\mu_{I}$, $m_{\pi^{\pm},\rm{scr}}$ monotonically decrease to zero on the boundary between the normal phase and the pion superfluid phase, while the screening mass of the neutral pion, $m_{\pi^0,\rm{scr}}$, remains almost unchanged. The pole mass $m_{\rm{pole}}$ and thermal width $\Gamma$ of the pion are extracted from the pole of temporal two-point Retarded correlation function, i.e., the corresponding quasi-normal frequencies, $\omega=m_{\rm{pole}}-i\Gamma/2$. The results show that the pole masses of the three modes ($\pi^0, \pi^+, \pi^-$) are splitting at finite $\mu_{I}$. The thermal widths of the three modes monotonically increase with temperature. Furthermore, the pole mass of $\pi^+$ decreases almost linearly with the increasing of $\mu_{I}$ and reaches zero at $\mu_{I}=\mu_{I}^c$, It means that $\pi^+$ becomes a massless Goldstone boson of the pion superfluid phase transition.

Abstract: In this paper, we study a possible early universe source for the recent observation of a stochastic gravitational wave background at the NANOGrav pulsar timing array. The source is a tachyonic instability in a dark gauge field induced by an axion-like particle (ALP), a known source for gravitational waves. We find that relative to the previous analysis with the NANOGrav 12.5-year data set, the current 15-year data set favors parameter space with a relatively larger axion mass and decay constant. This favored parameter space is heavily constrained by $\Delta N_{\rm eff}$ and overproduction of ALP dark matter. While there are potential mechanisms for avoiding the second problem, evading the $\Delta N_{\rm eff}$ constraint remains highly challenging. In particular, we find that the gravitational wave magnitude is significantly suppressed with respect to the gauge boson dark radiation, which implies that successfully explaining the NANOGrav observation requires a large additional dark radiation, violating the cosmological constraints.

Abstract: We consider the small excesses around 95 GeV found in several searches for a new scalar in $\gamma \gamma$, $\tau \tau$ and $b \bar b$ final states. Instead of trying to accommodate them all, as is usually done in the literature, in the context of a given Standard Model~(SM) extension, we investigate whether it would be possible that one or two of these excesses correspond to an actual new scalar, while the remaining ones are merely statistical fluctuations. To this end, we use as benchmark model the UN2HDM, a SM extension with one scalar doublet, one scalar singlet, and an extra $\text{U}(1)'$ symmetry, which has been previously studied in the context of multiboson cascade decays. We show that most of the possibilities where the excesses in one or two of these channels disappear in the future can be accommodated by type-I or type-III UN2HDMs.

Abstract: We extract transverse momentum dependent feed-down fractions for bottomonium production using a data-driven approach. We use data published by the ATLAS, CMS, and LHCb collaborations for sqrt(s) = 7 TeV proton-proton collisions. Based on this collected data, we produce fits to the differential cross sections for the production of both S- and P-wave bottomonium states. Combining these fits with branching ratios for excited state decays from the Particle Data Group, we compute the feed-down fractions for both the Upsilon(1S) and Upsilon(2S) as a function of transverse momentum. Our results indicate a strong dependence on transverse momentum, which is consistent with prior extractions of the feed-down fractions. When evaluated at the average momentum of the states, we find that approximately 75% of Upsilon(1S) and Upsilon(2S) states are produced directly. Our results for the transverse momentum dependent feed-down fractions are provided in tabulated form so that they can be used by other research groups.