Based on the recently introduced black-bounce spacetimes, we shall consider the construction of the related spherically symmetric thin-shell traversable wormholes within the context of standard general relativity. All of the really unusual physics is encoded in one simple parameter $a$ which characterizes the scale of the bounce. Keeping the discussion as close as possible to standard general relativity is the theorist’s version of only adjusting one feature of the model at a time. We shall modify the standard thin-shell traversable wormhole construction, each bulk region now being a black-bounce spacetime, and with the physics of the thin shell being (as much as possible) derivable from the Einstein equations. Furthermore, we shall apply a dynamical analysis to the throat by considering linearized radial perturbations around static solutions and demonstrate that the stability of the wormhole is equivalent to choosing suitable properties for the exotic material residing on the wormhole throat. The construction is sufficiently novel to be interesting and sufficiently straightforward to be tractable.

We show that a minimal local $B-L$ symmetry extension of the standard model can provide a unified description of both neutrino mass and dark matter. In our model, $B-L$ breaking is responsible for neutrino masses via the seesaw mechanism, whereas the real part of the $B-L$ breaking Higgs field (called $\sigma$ here) plays the role of a freeze-in dark matter candidate for a wide parameter range. Since the $\sigma$ particle is unstable, for it to qualify as dark matter, its lifetime must be longer than ${10}^{25}$ seconds implying that the $B-L$ gauge coupling must be very small. This in turn implies that the dark matter relic density must arise from the freeze-in mechanism. The dark matter lifetime bound combined with dark matter relic density gives a lower bound on the $B-L$ gauge boson mass in terms of the dark matter mass. We point out parameter domains where the dark matter mass can be both in the keV to MeV range as well as in the PeV range. We discuss ways to test some parameter ranges of this scenario in collider experiments. Finally, we show that if instead of $B-L$, we consider the extra $U(1)$ generator to be $-4I_{3R}+3(B-L)$, the basic phenomenology remains unaltered and for certain gauge coupling ranges, the model can be embedded into a five-dimensional $SO(10)$ grand unified theory.

White dwarfs (WD) effectively act as high-gain amplifiers for relatively small energy deposits within their volume via their supernova instability. In this paper, we consider the ways a galactic abundance of $\mathcal{O}(1)$-charged massive relics (i.e., CHAMPs) could trigger this instability, thereby destroying old WD. The dense central core structure formed inside the WD when heavy CHAMPs sink to its center can trigger a supernova via injection of energy during collapse phases, via direct density-enhanced (pycnonuclear) fusion processes of carbon nuclei dragged into the core by the CHAMPs, or via the formation of a black hole (BH) at the center of the WD. In the latter scenario, Hawking radiation from the BH can ignite the star if the BH forms with a sufficiently small mass; if the BH instead forms at large enough mass, heating of carbon nuclei that accrete onto the BH as it grows in size may be able to achieve the same outcome (with the conservative alternative being simply that the WD is devoured by the BH). The known existence of old WD that have not been destroyed by these mechanisms allows us to improve by many orders of magnitude on the existing CHAMP abundance constraints in the regime of large CHAMP mass, $m_X\sim {10}^{11}–{10}^{18}\mathrm{GeV}$. Additionally, in certain regions of parameter space, we speculate that this setup could provide a trigger mechanism for the calcium-rich gap transients: a class of anomalous, subluminous supernova events that occur far outside of a host galaxy.

The even-weight modular forms of level $N$ can be arranged into the common irreducible representations of the inhomogeneous finite modular group ${\mathrm{\Gamma }}_N$ and the homogeneous finite modular group ${\mathrm{\Gamma }}_N^{\prime }$ which is the double covering of ${\mathrm{\Gamma }}_N$, and the odd-weight modular forms of level $N$ transform in the new representations of ${\mathrm{\Gamma }}_N^{\prime }$. We find that the above structure of modular forms can naturally generate texture zeros of the fermion mass matrices if we properly assign the representations and weights of the matter fields under the modular group. We perform a comprehensive analysis for the ${\mathrm{\Gamma }}_3^{\prime }\cong T^{\prime }$ modular symmetry. The three generations of left-handed quarks are assumed to transform as a doublet and a singlet of $T^{\prime }$, and we find six possible texture-zero structures of the quark mass matrix up to row and column permutations. We present five benchmark quark models which can produce very good fits to the experimental data. These quark models are further extended to include the lepton sector, and the resulting models can give a unified description of both quark and lepton masses and flavor mixing simultaneously, although they contain a smaller number of free parameters than the observables.

We study the impacts of dimension-five lepton-number violating operators associated with two same-sign weak bosons, ${\ell }^{\pm }{\ell }^{\prime \pm }{W}^{\mp }{W}^{\mp }$, on current and future experiments for neutrino oscillation, lepton-number violating rare processes and high-energy collider experiments. These operators can contain important information on the origin of tiny neutrino masses, which is independent of that from the so-called Weinberg operator. We examine constraints on the coefficients of the operators by the neutrino oscillation data. Upper bounds on the coefficients are also investigated by using the data for processes of lepton number violation such as neutrinoless double beta decays and ${\mu }^{-}\text{−}{e}^{+}$ conversion. These operators can also be directly tested by searching for lepton-number violating dilepton production via the same-sign W boson fusion process at high-energy hadron colliders like the Large Hadron Collider. We find that these operators can be considerably probed by these current and future experiments.

In a nonperturbative gauge-invariant formulation of grand unified theories all low-energy vector states need to be composite with respect to the high-scale gauge group, including the photon. We investigate this by using lattice methods to spectroscopically analyze the vector channel in a toy grand unified theory: an SU(2) adjoint Higgs model. Our results indeed support the existence of a massless composite vector particle.

We present a method for efficiently finding solutions of Lüscher’s quantization condition, the equation which relates two-particle scattering amplitudes to the discrete spectrum of states in a periodic spatial volume of finite extent such as that present in lattice QCD. The approach proposed is based on an eigenvalue decomposition in the space of coupled-channels and partial-waves, which proves to have several desirable and simplifying features that are of great benefit when considering problems beyond simple elastic scattering of spinless particles. We illustrate the method with a toy model of vector-vector scattering featuring a high density of solutions, and with an application to explicit lattice QCD energy level data describing $J^P=1^{-}$ and $1^{+}$ scattering in several coupled channels.

We have systematically investigated the mass spectrum and rearrangement decay properties of the exotic tetraquark states with four different flavors using a color-magnetic interaction model. Their masses are estimated by assuming that the $X(4140)$ is a $cs\overline{c}\overline{s}$ tetraquark state and their decay widths are obtained by assuming that the Hamiltonian for decay is a constant. According to the adopted method, we find that the most stable states are probably the isoscalar $bs\overline{u}\overline{d}$ and $cs\overline{u}\overline{d}$ with $J^P=0^{+}$ and $1^{+}$. The width for most unstable tetraquarks is about tens of MeVs, but that for unstable $cu\overline{s}\overline{d}$ and $cs\overline{u}\overline{d}$ can be around 100 MeV. For the $X(5568)$, our method cannot give consistent mass and width if it is a $bu\overline{s}\overline{d}$ tetraquark state. For the $I(J^P)=0(0^{+}),0(1^{+})$ double-heavy $T_{bc}=bc\overline{u}\overline{d}$ states, their widths can be several MeVs.

Single-charm baryons can be classified into two $SU(3{)}_F$ multiplets: (i) the ${\overline{\mathbf{3}}}_F$-plet and (ii) the ${\mathbf{6}}_F$-plet. Each $SU(3{)}_F$ multiplet of charmed baryons has at most four different chiral $S{U}_L(3)\times S{U}_R(3)$ symmetry multiplets associated with it, i.e., each physical state is a mixture of at most four “chiral” states. Chiral symmetry imposes conditions/constraints on the interaction Lagrangians involving different chiral multiplets. We construct effective chiral Lagrangians for hadronic interactions describing transitions, scatterings, and decays of a single-charm baryon with a single pseudoscalar meson belonging to the $SU(3{)}_F$ nonet (containing the $\pi$, $K$, $\eta$, ${\eta }^{\prime }$ mesons). For this purpose, we use chiral transformation properties of light diquarks in the linear realization of chiral symmetry. We discuss the $U_A(1)$ symmetry of these chiral interactions and show that this symmetry imposes selection rules that ought to have observable consequences, at least in principle.

We evaluate axial vector transition form factors in holographic QCD models that have been shown to reproduce well recent experimental and theoretical results for the pion transition form factor. Comparing with L3 data on $f_1\to \gamma {\gamma }^{*}$ we find remarkable agreement regarding the shape of single-virtual form factors. In the double-virtual case, the holographic results differ strongly from a simple dipole form, and this has an important impact on the corresponding estimate of the axial vector contribution to the anomalous magnetic moment of the muon $a_{\mu }$ through hadronic light-by-light scattering. We demonstrate that hard-wall models satisfy the Melnikov-Vainshtein short-distance constraint for the latter, if and only if the infinite tower of axial vector states is included. The results for $a_{\mu }$, however, are strongly dominated by the first few resonances. Numerically, these results turn out to be surprisingly large: $(2.9–4.1)\times {10}^{-10}$ in the hard-wall models, 57%–58% of which are due to the longitudinal contribution, which is the one responsible for the Melnikov-Vainshtein short-distance constraint. Rescaling the holographic result to obtain an optimal fit of L3 data, but then matching only 52% of the asymptotic constraint, the result is reduced to $2.2(5)\times {10}^{-10}$, which is still significantly larger than most previous phenomenological estimates of the axial vector exchange contribution.

Cohen, Kaplan, and Nelson (CKN) conjectured that the UV and IR cutoffs of effective quantum field theories coupled to gravity are not independent, but are connected by the physics of black holes. We interpret the CKN bound as a scale-dependent depletion of the quantum field theory (QFT) density of states and discuss various aspects of the bound on small and large scales. For laboratory experiments, we argue that the bound provides small corrections to ordinary quantum field theory, which we estimate to be of order $m_e/M_p$ for $g-2$ of the electron. On large scales, we suggest a modification of the CKN bound due to the presence of cosmological horizons and discuss the connection with entropy bounds.

We establish a formal connection between the $k$-essence emergent gravity scenario and generalizations of Vaidya spacetime. Choosing the $k$-essence action to be of the Dirac-Born-Infeld variety, the physical spacetime to be a general static spherically symmetric black hole, and restricting the $k$-essence scalar field to be a function solely of the advanced or the retarded time, we show that the emergent gravity metric resembles closely the generalized Vaidya metrics for null fluid collapse proposed by Husain. Imposing null energy conditions on the emergent energy-momentum tensor derived from the emergent Einstein equation, restrictions are obtained on the functions characterizing the emergent metric for consistent identification with generalized Vaidya spacetimes. We discuss the possibility of dynamical horizons in the $k$-essence emergent Vaidya spacetime. Admissible explicit black hole background metrics are discussed as examples.

The quasinormal modes of a massless Dirac field in the de Rham-Gabadadze-Tolley (dRGT) massive gravity theory with asymptotically de Sitter spacetime are investigated using the Wentzel-Kramers-Brillouin approximation. The effective potential for the massless Dirac field due to the dRGT black hole is derived. It is found that the shape of the potential depends crucially on the structure of the graviton mass and the behavior of the quasinormal modes is controlled by the graviton mass parameters. Higher potentials give stronger damping of the quasinormal modes. We compare our results to the Schwarzschild-de Sitter case. Our numerical calculations are checked using Padé approximation and found that the quasinormal mode frequencies converge to ones with reasonable accuracy.

Phantom dark energy ($w<-1$) can produce amplified cosmic acceleration at late times, thus increasing the value of $H_0$ favored by CMB data and releasing the tension with local measurements of $H_0$. We show that the best fit value of $H_0$ in the context of the CMB power spectrum is degenerate with a constant equation-of-state parameter $w$, in accordance with the approximate effective linear equation $H_0+30.93w-36.47=0$ ($H_0$ in $\mathrm{km}{\sec }^{-1}{\mathrm{Mpc}}^{-1}$). This equation is derived by assuming that both ${\mathrm{\Omega }}_{0m}{h}^2$ and $d_A={\int }_0^{z_{\mathrm{rec}}}\frac{dz}{H(z)}$ remain constant (for an invariant CMB spectrum) and equal to their best fit Planck/$\mathrm{\Lambda }\mathrm{CDM}$ values as $H_0$, ${\mathrm{\Omega }}_{0m}$, and $w$ vary. For $w=-1$, this linear degeneracy equation leads to the best fit $H_0=67.4\mathrm{km}{\sec }^{-1}{\mathrm{Mpc}}^{-1}$ as expected. For $w=-1.22$, the corresponding predicted CMB best fit Hubble constant is $H_0=74\mathrm{km}{\sec }^{-1}{\mathrm{Mpc}}^{-1}$, which is identical with the value obtained by local-distance ladder measurements, while the best fit matter density parameter is predicted to decrease, since ${\mathrm{\Omega }}_{0m}{h}^2$ is fixed. We verify the above $H_0-w$ degeneracy equation by fitting a $w\mathrm{CDM}$ model with fixed values of $w$ to the Planck TT spectrum, showing also that the quality of fit (${\chi }^2$) is similar to that of $\mathrm{\Lambda }\mathrm{CDM}$. However, when including SnIa, baryon acoustic oscillation, or growth data, the quality of fit becomes worse than $\mathrm{\Lambda }\mathrm{CDM}$ when $w<-1$. Finally, we generalize the $H_0-w(z)$ degeneracy equation for the parametrization $w(z)=w_0+w_{1}z/(1+z)$ and identify analytically the full $w_0-w_1$ parameter region (straight line) that leads to a best fit $H_0=74\mathrm{km}{\sec }^{-1}{\mathrm{Mpc}}^{-1}$ in the context of the Planck CMB spectrum. This exploitation of $H_0-w(z)$ degeneracy can lead to immediate identification of all parameter values of a given $w(z)$ parametrization that can potentially resolve the $H_0$ tension.

The simplest model that can produce inflation is a massive noninteracting scalar particle with potential $V=m^2{\varphi }^2/2$. However, ${\varphi }^2$ chaotic inflation is inconsistent with the observed upper bound on the tensor-to-scalar ratio, $r$. Recently it has been shown that, in the context of the Palatini formalism of gravity with an $R^2$ term, the ${\varphi }^2$ potential can be consistent with the observed bound on $r$ while retaining the successful prediction for the scalar spectral index, $n_s$. Here we show that the Palatini ${\varphi }^2{R}^2$ inflation model can also solve the super-Planckian inflaton problem of ${\varphi }^2$ chaotic inflation, and that the model can be consistent with Planck scale-suppressed potential corrections, as may arise from a complete quantum gravity theory. If $\alpha \gtrsim {10}^{12}$, where $\alpha$ is the coefficient of the $R^2$ term, the inflaton in the Einstein frame, $\sigma$, remains sub-Planckian throughout inflation. In addition, if $\alpha \gtrsim {10}^{20}$, then the predictions of the model are unaffected by Planck-suppressed potential corrections in the case where there is a broken shift symmetry, and if $\alpha \gtrsim {10}^{32}$, then the predictions are unaffected by Planck-suppressed potential corrections in general. The value of $r$ is generally small, with $r\lesssim {10}^{-5}$ for $\alpha \gtrsim {10}^{12}$. We calculate the maximum possible reheating temperature, $T_{R\max }$, corresponding to instantaneous reheating, for the different regimes of $\alpha$. We find that for $\alpha \approx {10}^{32}$, $T_{R\max }$ is approximately ${10}^{10}\mathrm{GeV}$, with larger values of $T_{R\max }$ for smaller $\alpha$. For the case of instantaneous reheating, we show that $n_s$ is in agreement with the 2018 Planck results to within $1\text{−}\sigma$, with the exception of the $\alpha \approx {10}^{32}$ case, which is close to the $2\text{−}\sigma$ lower bound. Following inflation, the inflaton condensate is likely to rapidly fragment, which makes it possible for reheating to occur via the Higgs portal due to inflaton annihilations within oscillons. This typically results in delayed reheating, which is disfavored by the observed value of $n_s$. In contrast, reheating via inflaton decays to right-handed neutrinos can easily result in instantaneous reheating. We determine the scale of unitarity violation and show that, in general, unitarity is conserved during inflation, although the inflaton field is larger than the unitarity-violation scale. We conclude that the Palatini ${\varphi }^2{R}^2$ inflation model provides a completely consistent model of inflation which can be sub-Planckian and consistent with Planck scale-suppressed potential corrections, can reheat successfully, and conserves unitarity during inflation.

In several relativistic astrophysics scenarios, the understanding of the rich magnetohydrodynamics is hampered by the limitations set by the achievable numerical resolution. In these cases, it is a tremendous challenge to accurately simulate numerically all the relevant scales. We present how to study such systems by using large eddy simulations with a self-consistent subgrid-scale gradient model that we generalized to the special relativistic case in a previous work and now extend to the general relativistic case. Adapted from nonrelativistic scenarios, the so-called gradient model allows us to capture part of the effects of the hidden dynamics on the resolved scales, by means of a physically agnostic, mathematically based Taylor expansion of the nonlinear terms in the conservative evolution equations’ fluxes. One of the main applications is the binary neutron star mergers, where the collision excites a nontrivial amplification at small spatial scales. Motivated by this scenario, we assess the validity of this approach in bounding-box simulations of the magnetic Kelvin-Helmholtz instability. Several resolutions and a broad range of scenarios are considered in order to carefully test the performance of the model under three crucial aspects: (i) highly curved backgrounds, (ii) jumps on the fluid density profiles, and (iii) strong shocks. The results suggest that our extension of the gradient subgrid-scale model to general relativistic magnetohydrodynamics is a promising approach for studying binary neutron star mergers and other relevant astrophysical scenarios.

We study several methods for timing the neutrino signal of a Galactic supernova (SN) for different detectors via Monte Carlo simulations. We find that, for the methods we studied, at a distance of 10 kpc both Hyper-Kamiokande and IceCube can reach precisions of $\sim 1\mathrm{ms}$ for the neutrino burst, while a potential IceCube Gen2 upgrade will reach submillisecond precision. In the case of a failed SN, we find that detectors such as SK and JUNO can reach precisions of $\sim 0.1\mathrm{ms}$ while HK could potentially reach a resolution of $\sim 0.01\mathrm{ms}$ so that the impact of the black hole formation process itself becomes relevant. Two possible applications for this are the triangulation of a (failed) SN as well as the possibility to constrain neutrino masses via a time-of-flight measurement using a potential gravitational wave signal as reference.

We present constraints on an astrophysical population of neutrino sources imposed by recent data from the IceCube neutrino observatory. By using the IceCube point source search method to model the detection of sources, our detection criterion is more sensitive than using the observation of high-energy neutrino multiplets for source identification. We frame the problem as a Bayesian hierarchical model to connect the high-level population parameters to the IceCube data, allowing us to consistently account for all relevant sources of uncertainty in our model assumptions. Our results show that sources with a local density of $n_0\gtrsim {10}^{-7}{\mathrm{Mpc}}^{-3}$ and luminosity $L\lesssim {10}^{43}\mathrm{erg}{\mathrm{s}}^{-1}$ are the most likely candidates, but that populations of rare sources with $n_0\simeq {10}^{-9}{\mathrm{Mpc}}^{-3}$ and $L\simeq {10}^{45}\mathrm{erg}{\mathrm{s}}^{-1}$ can still be consistent with the IceCube observations. We demonstrate that these conclusions are strongly dependent on the source evolution considered, for which we consider a wide range of models. In doing so, we present realistic, model-independent constraints on the population parameters that reflect our current state of knowledge from astrophysical neutrino observations. We also use our framework to investigate constraints in the case of possible source detections and future instrument upgrades. Our approach is flexible and can be used to model specific source cases and extended to include multimessenger information.

We examine the implications of a recently proposed theory of fermion masses and mixings in which an $A_4$ family symmetry emerges from orbifold compactification. We analyze two variant schemes concerning their predictions for neutrino oscillations, neutrinoless double-beta decay, and the golden quark-lepton unification mass relation. We find that upcoming experiments DUNE as well as LEGEND and nEXO offer good chances of exploring a substantial region of neutrino parameters.