We study tensor models based on $O(N{)}^r$ symmetry groups constructed out of rank-$r$ tensors with order-$q$ interaction vertices. We refer to those tensor models for which $r<q-1$ as subchromatic. We focus most of our attention on sextic ($q=6$) models with maximally single-trace interactions. We show that only three subchromatic sextic maximally single-trace interaction vertices exist: these are the $r=3$ prism, the $r=3$ wheel (or $K_{3,3}$) and the $r=4$ octahedron. For theories based on these interactions we demonstrate that the set of Feynman diagrams that contribute to the free energy in the large $N$ limit are melonic and thus can be explicitly summed. In order to take into account the prism, we generalize the conventional notion of melonic diagrams slightly to include diagrams generated by a new melonic move—vertex expansion.

For a long time, the predictive limits of perturbative quantum field theory have been limited by our inability to carry out loop calculations to an arbitrarily high order, which become increasingly complex as the order of perturbation theory is increased. This problem is exacerbated by the fact that perturbation series derived from loop diagram (Feynman diagram) calculations represent asymptotic (divergent) series which limits the predictive power of perturbative quantum field theory. Here, we discuss an ansatz that could overcome these limits, based on the observations that (i) for many phenomenologically relevant field theories, one can derive dispersion relations which relate the large-order growth (the asymptotic limit of “infinite loop order”) with the imaginary part of arbitrary correlation functions, for negative coupling (“unstable vacuum”), and (ii) one can analyze the imaginary part for negative coupling in terms of classical field configurations (instantons). Unfortunately, the perturbation theory around instantons, which could lead to much more accurate predictions for the large-order behavior of Feynman diagrams, poses a number of technical as well as computational difficulties. Here, we study, to further the above-mentioned ansatz, correlation functions in a one-dimensional (1D) field theory with a quartic self-interaction and an $O(N)$ internal symmetry group, otherwise known as the 1D $N$-vector model. Our focus is on corrections to the large-order growth of perturbative coefficients, i.e., the limit of a large number of loops in the Feynman diagram expansion. We evaluate, in momentum space, the two-loop corrections for the two-point correlation function, and its derivative with respect to the momentum, as well as the two-point correlation function with a wigglet insertion. Also, we study the four-point function. These quantities, computed at zero momentum transfer, enter the renormalization-group functions (Callan-Symanzik equation) of the model. Our calculations pave the way for further development of related methods in field theory and for a better understanding of field-theoretical expansions at large order.

The worldline of a uniformly accelerated localized observer in Minkowski space is restricted in the Rindler wedge, where the observer can in principle arrange experiments repeatedly, and the Cauchy problem for quantum fields in that Rindler wedge can be well defined. However, the observer can still receive the signals sourced by the events behind the past horizon, and coordinatize those events in terms of some kind of observational coordinates. We construct such observational coordinates in some simple cases with the localized observers in Minkowski, de Sitter, and Schwarzschild-like spacetimes, and compare them with radar coordinates for the same observers.

We study perturbation theory for large-scale structure in the most general scalar-tensor theories propagating a single scalar degree of freedom, which include Horndeski theories and beyond. We model the parameter space using the effective field theory of dark energy. For Horndeski theories, the gravitational field and fluid equations are invariant under a combination of time-dependent transformations of the coordinates and fields. This symmetry allows one to construct a physical adiabatic mode which fixes the perturbation-theory kernels in the squeezed limit and ensures that the well-known consistency relations for large-scale structure, originally derived in general relativity, hold in modified gravity as well. For theories beyond Horndeski, instead, one generally cannot construct such an adiabatic mode. Because of this, the perturbation-theory kernels are modified in the squeezed limit and the consistency relations for large-scale structure do not hold. We show, however, that the modification of the squeezed limit depends only on the linear theory. We investigate the observational consequences of this violation by computing the matter bispectrum. In the squeezed limit, the largest effect is expected when considering the cross-correlation between different tracers. Moreover, the individual contributions to the 1-loop matter power spectrum do not cancel in the infrared limit of the momentum integral, modifying the power spectrum on nonlinear scales.

The structure of hybrid stars within the nonperturbative framework of the field correlator method, extended to the zero-temperature limit as a quark model, has been studied. For the hadronic sector, we have used the lowest-order constraint variational method by employing $A{V}_{18}$ two-body nucleon-nucleon interaction supplemented by the phenomenological Urbana-type three-body force. For an adapted value of the gluon condensate, $G_2=0.006{\mathrm{GeV}}^4$, which gives the critical temperature of about $T_c\sim 170\mathrm{MeV}$, stable hybrid stars with a maximum mass of $2.04M_{\odot }$ are predicted. The stability of hybrid star has been investigated for a wide range of gluon condensate value, $G_2$, and quark-antiquark potential, $V_1$. A hybrid equation of state fulfills the constraints on tidal deformability and hence on the radii of the stars, extracted from the binary GW170817. Moreover, tidal deformability for different chirp masses and different binary mass ratios of hybrid stars have been studied. The mass-radius relation satisfies the new constraint obtained from the neutron star interior composition explorer (NICER). A comprehensive analysis on the structure of a hybrid star and also its compactness, tidal Love number, and tidal deformability has been conducted for several parameter sets of the quark equation of state. The influence of different crustal equations of state on the mentioned quantities has been studied. Our calculations suggest the value of quark-antiquark potential, $V_1$, to be around 0.08 GeV. The results achieved in this study are in strong concurrence with the other calculations reported on this subject.

We propose a method to probe the coupling of the Higgs to strange quarks by tagging strange jets at future lepton colliders. For this purpose we describe a jet-flavor observable, $J_F$, that is correlated with the flavor of the quark associated with the hard part of the jet. Using this variable, we set up a strangeness tagger aimed at studying the decay $h\to s\overline{s}$. We determine the sensitivity of our method to the strange Yukawa coupling, and find it to be of the order of the standard-model expectation.

The production of $W^{\pm }H$, $ZH$, $W^{+}{W}^{-}$, and $W^{\pm }Z$ pairs probes non-Standard-Model interactions of quarks, gauge bosons, and the Higgs boson. New effects can be parametrized in terms of an effective field theory (EFT) where the Lagrangian is expanded in terms of higher-dimension operators suppressed by increasing powers of a high scale $\mathrm{\Lambda }$. We examine the importance of including next-to-leading-order QCD corrections in global fits to the coefficients of the EFT. The numerical implications on the fits due to different approaches to enforcing the validity of the EFT are quantified. We pay particular attention to the dependence of the fits on the expansion in $1/{\mathrm{\Lambda }}^2$ since the differences between results calculated at $\mathcal{O}(1/{\mathrm{\Lambda }}^2)$ and $\mathcal{O}(1/{\mathrm{\Lambda }}^4)$ may give insight into the possible significance of dimension-eight effects.

As a next step in the exploration of a class of flavored gauge mediation models of supersymmetry breaking in which the mixing of the Higgs and messenger doublets are connected by a discrete non-Abelian symmetry, we investigate the generation of nontrivial mass hierarchies and mixing angles for the Standard Model matter fields. We consider here the case in which the Higgs-messenger symmetry, which we take for concreteness to be the discrete group ${\mathcal{S}}_3$, also plays the role of a (partial) family symmetry. Within the specific implementation of ${\mathcal{S}}_3$ studied here, we show that couplings at the renormalizable level can result in hierarchical quark masses, but do not lead to phenomenologically viable quark mixing parameters, requiring the inclusion of higher-dimensional operators. As a concrete exploration of this idea, we show that the Cabibbo angle can be generated within this framework via such nonrenormalizable couplings and explore the phenomenological implications of this scenario.

We consider an ultralight scalar coupled to the Higgs in the presence of heavier new physics. In the electroweak broken phase the Higgs gives a tree-level contribution to the light-scalar potential, while new physics contributes at loop level. Thereby, the theory has a cosmologically metastable phase where the light scalar is around the top of its potential, and the Higgs is a loop factor lighter than new physics. Such regions with precarious naturalness are anthropically and environmentally selected, as regions with heavier Higgs crunch quickly. We expect observable effects of rolling in the dark-energy equation of state. Furthermore, vacuum energies up to the weak scale can be canceled down to anthropically small values.

Given the elusive nature of neutrinos, their self-interactio is particularly difficult to probe. Nevertheless, upper limits on the strength of such an interaction can be set by using data from terrestrial experiments. In this work, we focus on additional contributions to the invisible decay width of $Z$ boson as well as the leptonic $\tau$ decay width in the presence of a neutrino coupling to a relatively light scalar. For invisible $Z$ decays, we derive a complete set of constraints by considering both three-body bremsstrahlung as well as the loop correction to two-body decays. While the latter is usually regarded to give rather weak limits, we find that through the interference with the Standard Model diagram it actually yields a competitive constraint. As far as leptonic decays of $\tau$ are concerned, we derive a limit on neutrino self-interactions that is valid across the whole mass range of a light scalar mediator. Our bounds on the neutrino self-interaction are leading for $m_{\varphi }\gtrsim 300\mathrm{MeV}$ and interactions that prefer ${\nu }_{\tau }$. Bounds on such $\nu$-philic scalars are particularly relevant in light of the recently proposed alleviation of the Hubble tension in the presence of such couplings.

The study of Yang-Mills theories in three dimensions is an insightful playground to grasp important features for the four-dimensional case. Additionally, in three dimensions, the Chern-Simons term can be introduced with a mass parameter of topological nature. Quantizing such a theory in the continuum demands a gauge fixing which, in general, is plagued by Gribov copies. In this work, Yang-Mills-Chern-Simons theories are quantized in the maximal Abelian gauge and the existence of infinitesimal Gribov copies is taken into account. The elimination of copies modifies the (Abelian) gluon propagator leading to two different phases: one in which all poles are complex and thus interpreted as a confining phase and another where an excitation which can be part of the physical spectrum is present.

During a winter thunderstorm on 24 November 2017, a downward terrestrial gamma-ray flash took place and triggered photonuclear reactions with atmospheric nitrogen and oxygen nuclei, coincident with a lightning discharge at the Kashiwazaki-Kariwa nuclear power station in Japan. We directly detected neutrons produced by the photonuclear reactions with gadolinium orthosilicate scintillation crystals installed at sea level. Two gadolinium isotopes included in the scintillation crystals, ${}^{155}\mathrm{Gd}$ and ${}^{157}\mathrm{Gd}$, have large cross sections of neutron captures to thermal neutrons such as ${}^{155}\mathrm{Gd}(n,\gamma ){}^{156}\mathrm{Gd}$ and ${}^{157}\mathrm{Gd}(n,\gamma ){}^{158}\mathrm{Gd}$. Deexcitation gamma rays from ${}^{156}\mathrm{Gd}$ and ${}^{158}\mathrm{Gd}$ are self-absorbed in the scintillation crystals, and make spectral-line features which can be distinguished from other non-neutron signals. The neutron burst lasted for $\sim 100\mathrm{ms}$, and neutron fluences are estimated to be $>52$ and $>31\mathrm{neutrons}{\mathrm{cm}}^{-2}$ at two observation points inside the power station. Gadolinium orthosilicate scintillators work as valid detectors for thermal neutrons in lightning.

The radiative correction to the beta function is comprehensively studied at the one-loop level in the context of universal extra dimensions. Instead of using cutoffs to regularize one-loop divergences, the dimensional regularization scheme is used. In this approach, large momenta effects are removed from physical amplitudes by adjusting the parameters of the appropriate counterterms. The use of a $\mathrm{SU}(N)$-covariant gauge-fixing procedure to quantize the theory is stressed. One-loop contributions of Kaluza-Klein (KK) excitations are characterized by discrete KK sums and continuous momenta sums, which can diverge. Two types of ultraviolet divergences are identified, one arising from poles of the gamma function and associated with short-distance effects in the usual four-dimensional spacetime manifold and the other emerging either from poles of the one-dimensional Epstein function or from the gamma function and corresponding to short-distance effects in the compact manifold. We address the cases of 5 and $4+n$ dimensions ($n\ge 2$) separately. In five dimensions, the one-dimensional Epstein function is convergent, so the usual counterterm renormalizes the vacuum-polarization function. For $4+n$ dimensions, the one-dimensional Epstein function is divergent, so renormalization is implemented by interactions of canonical dimension higher than 4, already present in the effective theory. The polarization function is renormalized using both a mass-dependent scheme and a mass-independent scheme, with extra-dimensions effects decoupling in the former case but not in the latter. The beta function is calculated for an arbitrary number of extra dimensions. Our main result is that Yang-Mills theory remains perturbative at the one-loop level, which is in disagreement with the results obtained in the literature by using a cutoff regulator, which suggest that Yang-Mills theory in more than four dimensions ceases to be perturbative. We emphasize the advantages of a mass-dependent scheme in this type of theories, in which decoupling is manifest.

We study the $DN$ and $D^{*}N$ interactions to probe the inner structure of ${\mathrm{\Sigma }}_c(2800)$ and ${\mathrm{\Lambda }}_c(2940)$ with the chiral effective field theory to the next-to-leading order. We consider the contact term, one-pion-exchange and two-pion-exchange contributions to characterize the short-, long-, and mid-range interactions of the $D^{(*)}N$ systems. The low energy constants of the $D^{(*)}N$ systems are related to those of the $N\overline{N}$ interaction with a quark level Lagrangian that was inspired by the resonance saturation model. The $\mathrm{\Delta }(1232)$ degree of freedom is also included in the loop diagrams. The attractive potential in the $[DN{]}_{J=1/2}^{I=1}$ channel is too weak to form a bound state, which indicates that the explanation of ${\mathrm{\Sigma }}_c(2800)$ as the compact charmed baryon is more reasonable. Meanwhile, the potentials of the isoscalar channels are deep enough to yield the molecular states. We obtain the masses of the $[DN{]}_{J=1/2}^{I=0}$, $[D^{*}N{]}_{J=1/2}^{I=0}$, and $[D^{*}N{]}_{J=3/2}^{I=0}$ systems to be 2792.0, 2943.6, and 2938.4 MeV, respectively. The ${\mathrm{\Lambda }}_c(2940)$ is probably the isoscalar $D^{*}N$ molecule considering its low mass puzzle. Besides, the ${\mathrm{\Lambda }}_c(2940)$ signal might contain the spin-$\frac{1}{2}$ and spin-$\frac{3}{2}$ two structures, which can qualitatively explain the significant decay ratio to $D^{0}p$ and ${\mathrm{\Sigma }}_c\pi$. We also study the ${\overline{B}}^{(*)}N$ systems and predict the possible molecular states in the isoscalar channels. We hope experimentalists could hunt for the open charmed molecular pentaquarks in the ${\mathrm{\Lambda }}_c^{+}{\pi }^{+}{\pi }^{-}$ final state.

Harko and Moraes [preceding Comment, Phys. Rev. D 101, 108501 (2020).] claim that in $f(R,T)$ gravity with $f(R,T)=f_1(R)+f_2(T)$, the term $f_2(T)$ cannot be incorporated in the matter Lagrangian ${\mathcal{L}}_m$. A careful examination of their Comment finds that they have made several dubious assumptions without indicating any errors in our work. Most notably, they have unjustifiably claimed that the two terms ${\mathcal{L}}_m$ and $f_2(T)$ are of “different origin,” and their inference that only the first contributes to the energy momentum tensor is arbitrary. Also significant, their derivation of equations of motion from a Lagrangian formulation, imposing conservation constraints ad hoc rather than via Lagrange multipliers, leads to inconsistent conclusions.

In a recent paper, “Reexamining $f(R,T)$ gravity”, by S. B. Fisher and E. D. Carlson [Phys. Rev. D 100, 064059 (2019), the authors claim that for the particular $f(R,T)$ modified gravity model, with $f(R,T)=f_1(R)+f_2(T)$, the term $f_2(T)$ must be included in the matter Lagrangian and therefore it does not have any physical significance. We carefully reexamine the line of reasoning presented in the paper, and we show that there are several major conceptual problems related to the author’s physical interpretations, as well as in the physical and mathematical approaches used to derive the energy-momentum tensor of the theory. These problems raise some serious concerns about the validity of most of the results presented in the paper.

Kink-antikink scattering in the ${\varphi }^4$ model is investigated in the limit when the static inter-soliton force vanishes. We observe the formation of spectral walls and, further, identify a new phenomenon, the vacuum wall, whose existence gives rise to a bouncing structure for the annihilating solitons. Furthermore, we discover higher order spectral walls, i.e., spectral walls which form when higher harmonics enter the continuous spectrum. These higher order spectral walls not only deform the soliton trajectories, they also can be observed easily as very intense radiation bursts.

We obtain full moduli parameters for generic nonplanar Bogomol’nyi-Prasad-Sommerfield networks of domain walls in an extended Abelian-Higgs model with $N$ complex scalar fields and exhaust all exact solutions in the corresponding $\mathbb{C}{P}^{N-1}$ model. We develop a convenient description by grid diagrams which are polytopes determined by mass parameters of the model. To illustrate the validity of our method, we work out nonplanar domain wall networks for lower $N$ in $3+1$ dimensions. In general, the networks can have compact vacuum bubbles, which are finite vacuum regions surrounded by domain walls, when the polytopes of the grid diagrams have inner vertices, and the size of bubbles can be controlled by moduli parameters. We also construct domain wall networks with bubbles in the shapes of the Platonic, Archimedean, Catalan, and Kepler-Poinsot solids.

We construct a nonunitary transformation that relates a given “asymptotically free” conformal quantum mechanical system $H_f$ with its confined, harmonically trapped version $H_c$. In our construction, Jordan states corresponding to the zero eigenvalue of $H_f$, as well as its eigenstates and Gaussian packets, are mapped into the eigenstates, coherent states, and squeezed states of $H_c$, respectively. The transformation is an automorphism of the conformal $\mathfrak{s}\mathfrak{l}(2,\mathbb{R})$ algebra of the nature of the fourth-order root of the identity transformation, to which a complex canonical transformation corresponds on the classical level being the fourth-order root of the spatial reflection. We investigate the one- and two-dimensional examples that reveal, in particular, a curious relation between the two-dimensional free particle and the Landau problem.

The approach of a quantum state to a cosmological singularity is studied through the evolution of its moments in a simple version of a Bianchi I model. In spite of the simplicity, the model exhibits several instructive and unexpected features of the moments. They are investigated here both analytically and numerically in an approximation in which anisotropy is assumed to vary slowly, while numerical methods are also used to analyze the case of a rapidly evolving anisotropy. Physical conclusions are drawn mainly regarding two questions. First, quantum uncertainty of anisotropies does not necessarily eliminate the existence of isotropic solutions, with potential implications for the interpretation of minisuperspace truncations as well as structure-formation scenarios in the early universe. Second, backreaction of moments on basic expectation values is found to delay the approach to the classical singularity.