<p>Atmospheric neutrino oscillations are important to the study of neutrino properties, including the neutrino mass ordering problem. A good capability to identify neutrinos’ flavor and neutrinos against antineutrinos is crucial in such measurements. In this paper, we present a machine-learning-based approach for identifying atmospheric neutrino events in a large homogeneous liquid scintillator detector. This method identifies features of photomultiplier tube waveforms that reflect event topologies and uses them as input to machine learning models. In addition, neutron-capture information is utilized to achieve neutrino vs antineutrino discrimination. Preliminary performances based on Monte Carlo simulations are presented, which demonstrate such a detector’s potential in future measurements of atmospheric neutrinos such as the one planned for the JUNO experiment.</p>

China

Jiaxi Liu

Fanrui Zeng

Hongyue Duyang

Wanlei Guo

Xinhai He

Teng Li

Zhen Liu

Wuming Luo

Wing Yan Ma

Xiaohan Tan

Liangjian Wen

Zekun Yang

Yongpeng Zhang

Neutrino type identification for atmospheric neutrinos in a large homogeneous liquid scintillation detector

Among the three known types of static solutions proposed within the Hamiltonian constraint approach to effective quantum gravity (EQG), the first two have been extensively investigated, whereas the third type-which preserves general covariance, is free of Cauchy horizons, and was only recently obtained-remains relatively unexplored. This solution can describe a black hole with an event horizon for certain parameter ranges, or a horizonless compact object beyond those ranges. In this paper, we focus on the third type and show that its light rings feature both stable and unstable branches, and that the black hole shadow size grows with the quantum parameter-unlike in the first two types. However, when we account for both the shadow and the lensing ring, the overall behavior closely resembles that of the second type, in which an increasing quantum parameter leads to a larger portion of the lensing ring being occupied by the shadow. This feature can serve as a hallmark of black holes in EQG, offering a potential way to distinguish them from their GR counterparts. Remarkably, the parameter ranges under which the solution remains a black hole are highly consistent with the current observational constraints on black hole shadows, lending strong support to the classification of the third type of compact object in EQG as a black hole endowed with an event horizon.

Wentao Liu

Di Wu

Jieci Wang

Light rings and shadows of static black holes in effective quantum gravity II: A new solution without Cauchy horizons

We study the thermal behavior of quarkonia and fully-heavy tetraquark states associated to the charmonium, bottomonium and bottom-charmonium mass spectra. The starting point is the Schrödinger formalism with a vacuum Cornell-like potential. The spin-spin, spin-orbit and tensor contributions are also considered to describe the structure of the vacuum quarkonia $$Q\bar{Q}$$ spectra ($\textit{Q}$ denoting $\textit{c}$, $\textit{b}$ quarks). The parameters of the model are fixed using the experimental data of the $$Q\bar{Q}$$ states. After that, this formalism is extended to the fully-heavy tetraquark states within the $$1^3 S_1$$ axial diquark– $$1^3 S_1$$ axial antidiquark configuration $$[QQ] [\bar{Q} \bar{Q}]$$ , and their vacuum mass spectra are obtained and compared to the experimental data recently obtained. Our predictions support the interpretation of the $\textit{X}$(6600) (or $\textit{X}$(6552)), $\textit{X}$(6900) and $\textit{X}$(7200) states as the radially-excited $$T_{4c}(n^1S_0)$$ configurations with $$n=2,3,4$$ . In the sequence, we evaluate the mass spectra behavior in a thermal medium, by introducing a modified temperature-dependent Cornell potential. As a consequence, this formalism enables us to get some insight into the dissociation mechanism of $$[QQ] [\bar{Q} \bar{Q}]$$ states caused by a thermal medium, and into the temperature range at which the tetraquark states might be formed. We find that these structures cannot be formed in the thermal medium when the system has a temperature higher than about twice the critical temperature. These findings may be useful to better understand the features of the exotics in heavy-ion collisions.

Brazil

Vinícius Silva

Cássio Pigozzo

Luciano Abreu

Fully-heavy tetraquarks in the vacuum and in a hot environment

The late-time cosmological expansion within a flat Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime is studied using a model characterized by bulk viscous dark matter (bulk viscosity $$\zeta = \zeta _0 \rho _m H^{-1}+\zeta _1 H $$ , $$\zeta _0$$ & $$\zeta _1$$ are constants, and $\textit{H}$, the Hubble parameter) interacting with a decaying vacuum density $$\rho _{\Lambda } = \mathcal {C}_0 + 3\nu H^2$$ , where $$\mathcal {C}_0$$ and $$\nu $$ are constants. The bulk viscous pressure is described by Eckart’s theory. The interaction term is defined as $$ Q=3H\alpha (\rho _m+\rho _\Lambda )$$ , where $$\alpha $$ , the interaction parameter. Analytical solutions for the Hubble parameter and the scale factor have been derived. The validity of the models is evaluated by constraining their free parameters using observational data from $\textit{Cosmic Chronometer}$, the $\textit{Pantheon}$, and a combination of both datasets. The goodness of fit is assessed by minimizing the $$\chi ^2$$ function utilizing the Markov Chain Monte Carlo (MCMC) method. Selection information criteria, namely AIC and BIC, have been obtained to analyze the models’ stability. Additionally, several essential cosmological parameters characterizing the evolution dynamics are estimated and discussed analytically, and compared with the $$\Lambda $$ CDM model. The proposed model suggests a transition from the deceleration to the acceleration phase, indicating thermodynamic equilibrium in the distant future, aligning with the $$\Lambda $$ CDM model. The model shows a slight deviation from $$\Lambda $$ CDM model and effectively reduces the $$H_0$$ tension between local measurements by $\textit{R}$21 and global measurements by Planck 2018. The model is consistent with thermodynamic laws and upholds the second law of thermodynamics. Finally, Phase-space analysis supports the same evolutionary transitional phases.

India

Tanmay Nandi

Amitava Choudhuri

Bulk viscous matter interacting with decaying vacuum energy density: a model for late-time evolution of the Universe

Scalar singlets under the Standard Model gauge group appear naturally in many well-motivated New Physics scenarios, such as the composite Higgs models. Unlike the Higgs boson in the Standard Model, they can induce large flavour-changing neutral currents (FCNCs) in the top sector. We investigate systematically the effects of a light scalar singlet $\textit{S}$ with top-quark FCNC couplings, by including the low-energy constraints from the $\textit{B}$ → $\textit{μ}$ decay, the muon anomalous magnetic moment ($\textit{g}$ − 2) and the neutron Electric Dipole Moment (EDM). We also perform a detailed Monte-Carlo simulation of the channel $\textit{pp}$ → $\textit{tS}$ + $\textit{j}$ with $\textit{S}$ → $\textit{μ}$ and $\textit{S}$ → $$ b\overline{b} $$ , and investigate the LHC sensitivity to the $\textit{tcS}$ couplings. It is found that the scalar singlet $\textit{S}$ can induce scalar-type contributions to the $\textit{B}$ $\textit{→ μ}$ decay, which do not suffer from the helicity suppression and contain a large CKM factor $$ {V}_{cs}^{\ast }{V}_{tb} $$ . As a result, constraints on the $\textit{tcS}$ couplings from the measured branching ratio $$ \mathcal{B} $$ ($\textit{B}$ → $\textit{μ}$ ) are quite stringent, being even stronger than the expected LHC sensitivity in some parameter spaces. Besides the CP-conserving $\textit{tcS}$ couplings, we have also considered the case of CP-violating $\textit{tcS}$ couplings, with $$ {y}_{R,L}^{ct}=\left|{y}_{R,L}^{ct}\right|{e}^{i{\theta}_{R,L}} $$ . It is found that the CP observables $$ {\mathcal{A}}_{\Delta {\varGamma}_s}^{\mu \mu} $$ and $$ {\mathcal{S}}_{\mu \mu} $$ of the $\textit{B}$ $\textit{→ μ}$ decay are sensitive to the phase $\textit{θ}$ , while the neutron EDM can provide bounds on the phase difference $\textit{θ}$ − $\textit{θ}$ . Therefore, they are complementary to each other in probing the CP phases of the $\textit{tcS}$ couplings.

Biao-Feng Hou

Xin-Qiang Li

Ya-Dong Yang

Xing-Bo Yuan

Ming-Wang Zhang

Phenomenological anatomy of top-quark FCNCs induced by a light scalar singlet

<p>Without invoking any cumulant determination at the input level, we present here the first calculations of direct estimates of the Lee-Yang zeros of the QCD partition function in (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math>)-flavor QCD. These zeros are obtained in the complex isospin chemical potential <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> plane using the unbiased exponential resummation formalism on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>N</mi><mi>τ</mi></msub><mo>=</mo><mn>8</mn></math> lattices and with physical quark masses. For different temperatures, we illustrate the stability of the zeros closest to the origin from which we subsequently procure the radius of convergence estimates. From the temperature-dependence study of the real and imaginary parts of these zeros, we try estimating one of the possible critical points forming the second-order pion condensate critical line in the isospin phase diagram. Further, we compare these resummed estimates with the corresponding Mercer-Roberts estimates of the subsequent Taylor series expansions of the first three partition function cumulants. We also outline comparisons between resummed and Taylor series results of these cumulants for real and imaginary values of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> and highlight the behavior of different expansion orders within and beyond the obtained resummed estimates of the radius of convergence. We also reestablish that this resummed radius of convergence can efficiently capture the onset of the overlap problem for finite real <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> simulations.</p>

Germany

Sabarnya Mitra

Estimates of Lee-Yang zeros and a possible critical point on the pion condensate boundary in the QCD isospin phase diagram using an unbiased exponential resummation on the lattice

We compute next-to-leading power corrections in the zero-jettiness variable for the production of colorless final states at hadron colliders at next-to-leading order in QCD. To assess if the process-independence of leading power contributions can be extended, we attempt to construct generic expansions of phase spaces and matrix elements squared through next-to-leading power in the zero-jettiness. We highlight challenges associated with the collinear limit, where universality no longer holds at the subleading power, making the result process-dependent. We show that quantities that need to be calculated in the collinear limit can be obtained using Berends-Giele currents, enabling computation of power corrections to high-multiplicity final states. As a concrete example, we apply our method to compute power corrections in the zero-jettiness for lepton pair as well as multi-photon production in $$ q\overline{q} $$ collisions.

Prem Agarwal

Kirill Melnikov

Ivan Pedron

Philip Pfohl

Power corrections to the production of a color-singlet final state in hadron collisions in the $\textit{N}$-jettiness slicing scheme at NLO QCD

Certain supersymmetric elementary string states with angular momentum can be viewed as small black rings in a five-dimensional string theory. These black rings have zero area event horizon. The 4D-5D connection relates these small rings to small black holes without angular momentum in one less dimension. Recent works have proposed saddle solutions that compute the supersymmetric index for small black holes using gravitational path integral. In this paper, we propose an analogous saddle solution for a five-dimensional small black ring. The dominant contribution comes from a black ring saddle that rotates in both independent planes in five dimensions and has a finite area event horizon. We also write the saddle solution as a three center Bena-Warner solution.

Subhodip Bandyopadhyay

Gurmeet Punia

Yogesh Srivastava

Amitabh Virmani

The gravitational index of a small black ring

The freeze-in mechanism describes the out-of-equilibrium production of dark matter (DM) particles via feeble couplings or non-renormalisable interactions with large suppression scales. In the latter case, predictions suffer from a strong sensitivity to the initial conditions of the universe, such as the details of reheating. In this work, we investigate how this sensitivity is altered in the presence of a cosmological first-order phase transition. We show that freeze-in via non-renormalisable interactions is not always dominated by the highest temperatures of the Standard Model (SM) thermal bath, but instead may be governed by the period immediately after the phase transition, during which the decaying scalar field transfers its energy density to the SM radiation. We refer to this alternative production regime as $\textit{DM phase-in}$. Using numerical and approximate analytical solutions of the relevant Boltzmann equations, we determine the conditions under which phase-in or conventional freeze-in production dominates the final DM abundance in terms of the type of interaction between the DM and SM particles, the amount of supercooling before and the evolution of the scalar field after the phase transition. In the phase-in regime, the DM abundance is correlated with the peak frequency of the gravitational wave signal associated with the phase transition, opening up new observational possibilities.

Cristina Benso

Felix Kahlhoefer

Henda Mansour

Dark matter phase-in: producing feebly-interacting particles after a first-order phase transition

An important theoretical achievement of the last century was the realization that strict renormalizability can be a powerful criterion to select Lagrangians in the framework of perturbative quantum field theory. The Standard Model Lagrangian (without gravity) is strictly renormalizable from a perturbative point of view. On the other hand, the inclusion of gravity seems not to respect this criterion, since general relativity is perturbatively non-renormalizable. The aim of this work is to provide concrete evidence that strict renormalizability is still a valid criterion even when applied to gravity. First, we show that adding quadratic curvature terms to the Einstein-Hilbert action gives rise to a strictly renormalizable theory known as quadratic gravity. Second, we argue that this unique theory represents the most conservative approach to quantum gravity and, at the same time, is highly predictive, as it can explain new physics beyond general relativity already in the sub-Planckian regime. In particular, it provides one of the best fits to the CMB anisotropies via Starobinsky inflation and makes sharp cosmological predictions that can be tested in the near future. Finally, we comment on the (super-)Planckian regime and conclude with a historical note.

Netherlands

Luca Buoninfante

Strict renormalizability as a paradigm for fundamental physics