Early dark energy (EDE) relies on scalar field dynamics to resolve the Hubble tension, by boosting the pre-recombination length scales and thereby raising the CMB-inferred value of the Hubble constant into agreement with late universe probes. However, the collateral effect of scalar field microphysics on the linear perturbation spectra appears to preclude a fully satisfactory solution. $H_0$ is not raised without the inclusion of a late universe prior, and the “$S_8$ tension,” a discrepancy between early- and late-universe measurements of the structure growth parameter, is exacerbated. What if EDE is not a scalar field? Here, we investigate whether different microphysics, encoded in the constitutive relationships between pressure and energy density fluctuations, can relieve these tensions. We show that EDE with an anisotropic sound speed can soften both the $H_0$ and $S_8$ tensions while still providing a quality fit to CMB data. Future observations from the CMB-S4 experiment may be able to distinguish the underlying microphysics at the $4\sigma$ level, and thereby test whether a scalar field or some richer physics is at work.

We introduce a new logotropic model based on a complex scalar field with a logarithmic potential that unifies dark matter and dark energy. The scalar field satisfies a nonlinear wave equation generalizing the Klein-Gordon equation in the relativistic regime and the Schrödinger equation in the nonrelativistic regime. This model has an intrinsically quantum nature and returns the $\mathrm{\Lambda }$ cold dark matter (CDM) model in the classical limit $\hslash \to 0$. It involves a new fundamental constant of physics $A/c^2=2.10\times {10}^{-26}\mathrm{g}{\mathrm{m}}^{-3}$ responsible for the late accelerating expansion of the Universe and superseding the Einstein cosmological constant $\mathrm{\Lambda }$. The logotropic model is almost indistinguishable from the $\mathrm{\Lambda }\mathrm{CDM}$ model at large (cosmological) scales but solves the CDM crisis at small (galactic) scales. It also solves the problems of the fuzzy dark matter model. Indeed, it leads to cored dark matter halos with a universal surface density ${\mathrm{\Sigma }}_0^{\mathrm{th}}=5.85(A/4\pi G{)}^{1/2}=133M_{\odot }/{\mathrm{pc}}^2$. This universal surface density is predicted from the logotropic model without adjustable parameter and turns out to be close to the observed value ${\mathrm{\Sigma }}_0^{\mathrm{obs}}=141_{-52}^{+83}{M}_{\odot }/{\mathrm{pc}}^2$. We also argue that the quantities ${\mathrm{\Omega }}_{\mathrm{dm},0}$ and ${\mathrm{\Omega }}_{\mathrm{de},0}$, which are usually interpreted as the present proportions of dark matter and dark energy in the $\mathrm{\Lambda }\mathrm{CDM}$ model, are equal to ${\mathrm{\Omega }}_{\mathrm{dm},0}^{\mathrm{th}}=\frac{1}{1+e}(1-{\mathrm{\Omega }}_{\mathrm{b},0})=0.2559$ and ${\mathrm{\Omega }}_{\mathrm{de},0}^{\mathrm{th}}=\frac{e}{1+e}(1-{\mathrm{\Omega }}_{\mathrm{b},0})=0.6955$ in very good agreement with the measured values ${\mathrm{\Omega }}_{\mathrm{dm},0}^{\mathrm{obs}}=0.2589$ and ${\mathrm{\Omega }}_{\mathrm{de},0}^{\mathrm{obs}}=0.6911$ (their empirical ratio 2.669 is close to the Euler number $e=2.71828\dots$). We point out, however, important difficulties with the logotropic model, similar to those encountered by the generalized Chaplygin gas model. These problems are related to the difficulty of forming large-scale structures due to an increasing speed of sound as the Universe expands. We discuss potential solutions to these problems, stressing in particular the importance to perform a nonlinear study of structure formation.

In this study, we present the first multidimensional core-collapse supernovae (CCSNe) simulations including QCD axions in order to assess the impact on the CCSN explosion mechanism. We include axions in our simulations through the nucleon-nucleon bremsstrahlung emission channel and as a pure energy-sink term under the assumption that the axions free-stream after being emitted. We perform both spherically symmetric (1D) and axisymmetric (2D) simulations. In 1D, we utilize a parametrized heating scheme to achieve explosions, whereas in 2D we self-consistently realize explosions through the neutrino heating mechanism. Our 2D results for a $20M_{\odot }$ progenitor show an impact of the axion emission on the shock behavior and the explosion time when considering values of the PecceiQuinn energy scale $f_a\le 2\times {10}^8\mathrm{GeV}$. The strong cooling due to the axion emission accelerates the contraction of the core and leads to more efficient neutrino heating and earlier explosions. For the axion emission formalism utilized, the values of $f_a$ that impact the explosion are close to, but in tension with current limits based on the neutrinos detected from SN 1987A. However, given the nonlinear behavior of the emission and the multidimensional nature of CCSNe,we suggest that a self-consistent, multidimensional approach to simulating CCSNe, including any late time accretion and cooling, is needed to fully explore the axion bounds from supernovae and the impact on the CCSN explosion mechanism.

We carry out an exhaustive analysis of lepton flavor violating processes within the simplest little Higgs model. Its discovery could be expected from either $\mu \to e$ conversion in nuclei, $\mu \to e\gamma$, or $\mu \to 3e$ decays. Then, the tau sector could help discriminate this model not only via $\tau \to \ell \gamma$ ($\ell =\mu$, $e$) and $\tau \to 3\ell$ decays, but also by means of $\ell \to \tau$ conversion in nuclei, which is promising in this respect. Although the model slightly violates custodial symmetry, acommodating the recent CDF $M_W$ measurement is in tension with electroweak precision data.

We present an analysis of the experimental data for parity violating electron scattering and atomic parity violation, including the effects of a dark photon. We derive the favored region of dark photon parameter space, which provides a good description of the experimental data from the Qweak Collaboration and the Jefferson Lab PVDIS Collaboration and simultaneously relieves the tension between the neutron skin thickness determined in the PREX-II experiment and nuclear-model predictions. In addition, we extract the parameter region required to explain the latest $W$-boson mass anomaly. Our results indicate that a heavy dark photon with mass above the $Z$-boson mass is favored, while other sources of new physics beyond the Standard Model in addition to the dark photon would also be expected.

We analyze in a model independent way the possibilities of digging out neutral exotic Higgs states, should they exist endowed with unconventional couplings with ordinary matter and gauge fields, at the 14 TeV run of the Large Hadron Collider, adding some comparative studies for 13.6 and 13 TeV runs. Flavor models, based on some discrete symmetry groups, with extended scalar sectors are known to yield exotic spin-0 states, both $CP$-even and $CP$-odd, with purely flavor off-diagonal Yukawa couplings. The gauge interaction of one such $CP$-even state is also unusual that, unlike the Standard Model Higgs boson, it does not couple to gauge boson pairs. Such unconventional properties immune these exotic states from receiving traditional collider and electroweak constraints, and hence those states could be light. Without committing to any specific model, exploiting their peculiar Yukawa and gauge properties, we explore the discovery potential of those exotic Higgs states through some interesting topologies by figuring out some specific kinematic variables that suppress the backgrounds.

If dark matter has a sizable scattering cross section with nucleons, it can efficiently be captured by a neutron star. Its energy is then transferred to the neutron star as heat through the scattering and annihilation inside the star. This heating effect may be detectable via dedicated temperature observations of nearby old pulsars, providing an alternative method for dark matter searches. In this paper, we show that for electroweak multiplet dark matter, this search strategy can probe the parameter region which is out of reach of future dark matter direct detection experiments. To see this systematically, we classify such dark matter candidates in terms of their electroweak charges and investigate the effect of ultraviolet physics by means of higher-dimensional effective operators. We then show that if the effect of ultraviolet physics is sizable, the dark matter-nucleon elastic scattering cross section becomes sufficiently large, whilst if it is suppressed, then the mass splittings among the components of the dark matter multiplet get small enough so that the inelastic scattering processes are operative. In any case, the electroweak multiplet dark matter particles are efficiently captured in neutron stars, making the search strategy with the temperature observation of old neutron stars promising.

We consider an extension to the Standard Model (SM) with two extra real singlet scalars which interact with the SM Higgs particle. The lighter scalar is taken as the dark matter (DM) candidate. We show that the model successfully explains the relic abundance of the DM in the universe and evades the strong bounds from direct detection experiments while respecting the perturbativity and the vacuum stability conditions. In addition, we study the hierarchy problem within the Veltman approach by solving the renormalization group equations at one-loop. We demonstrate that the addition of the real singlet scalars contributes to the Veltman parameters which in turn results in satisfying the Veltman conditions much lower than the Planck scale ${\mathrm{\Lambda }}_{\mathrm{Pl}}$ down to the electroweak scale. Therefore, the presence of the extra scalars solves the fine-tuning problem of the Higgs mass. For the case of the two-scalar DM model we find two representative points in the viable parameter space which satisfy also the Veltman conditions at $\mathrm{\Lambda }=300\mathrm{GeV}$ and $\mathrm{\Lambda }=1\mathrm{TeV}$.

The total and differential cross sections of high-energy pion-proton and pion-pion scattering are investigated in a holographic QCD model, focusing on the Regge regime in which the Pomeron exchange gives the dominant contribution to those cross sections. The Pomeron is described by the Reggeized spin-2 particle propagator, and the hadron-Pomeron couplings are given by gravitational form factors of the hadrons, which are obtained from the bottom-up AdS/QCD models. Since the parameters, which characterize the Pomeron trajectory, have been determined in a preceding study of the proton-proton scattering, the pion-proton cross sections can be expressed with a single adjustable parameter. Once this parameter is determined by the experimental data of the pion-proton total cross section, its differential cross section and the pion-pion cross sections can be calculated without any additional parameter. Although the currently available data are limited, it is found that our calculation is consistent with those. Our predictions are explicitly shown, and the present model can be tested at the future experimental facilities.

We derive exact yet practical covariant equations of quantum field theory describing a tetraquark in terms of a mix of four-quark states $2q2\overline{q}$, and two-quark states $q\overline{q}$. A feature of our approach is that it avoids the overcounting problems that usually plague quantum field theory formulations of few-body covariant equations (the only exception being the two-body Bethe-Salpeter equation). This is achieved by describing the coupling of $2q2\overline{q}$ to $q\overline{q}$ states through the use of model operators that contract a four-quark $q\overline{q}$-irreducible Green function down to a two-quark $q\overline{q}$ Bethe-Salpeter kernel. Although the model chosen in the current work describes the four-quark dynamics in terms of meson-meson and diquark-antidiquark states, the derived equations have a form that is exact, as all corrections due to the use of a particular model are taken into account through the use of a well-defined special four-point amplitude $\mathrm{\Delta }$ entering the equations. The equations are in agreement with those obtained previously by consideration of disconnected interactions; however, despite being more general, they have been derived here in a much simpler and more transparent way.

The nonleptonic two-body ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\psi$ decays with $\psi =J/\psi$ or $\psi (2S)$ are investigated based on the perturbative QCD approach. These are color-suppressed processes in which the nonfactorizable contributions are confirmed to be dominant. Angular momentum conservation allows us to describe the concerned decays by four independent complex helicity amplitudes. It is observed that the negative-helicity states for the $\mathrm{\Lambda }$ baryon are preferred as expected in the left-handed nature of the charged-current interaction. The obtained results for the helicity amplitudes are used to compute the branching ratios and various observable parameters, which are then compared to the existing theoretical predictions and experimental data. In particular, we predict the ratio $\mathcal{R}=\frac{\mathcal{B}({\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\psi (2S))}{\mathcal{B}({\mathrm{\Lambda }}_b\to \mathrm{\Lambda }J/\psi )}=0.47_{-0.00}^{+0.02}$ in comparison with $0.508\pm 0.023$ from the Particle Data Group at the level of 1 standard deviation. We also briefly explore the long-distance contributions to the semileptonic ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }{l}^{+}{l}^{-}$ decays in the kinematic regions where the dilepton invariant masses are around the $J/\psi$ and $\psi (2S)$ resonances.

We present the first measurement of the negative pion total hadronic cross section on argon in a restricted phase space, which we performed at the Liquid Argon In A Testbeam (LArIAT) experiment. All hadronic reaction channels, as well as hadronic elastic interactions with scattering angle greater than 5° are included. The pions have kinetic energies in the range 100–700 MeV and are produced by a beam of charged particles impinging on a solid target at the Fermilab test beam facility. LArIAT employs a 0.24 ton active mass liquid argon time projection chamber (LArTPC) to measure the pion hadronic interactions. For this measurement, LArIAT has developed the “thin slice method,” a new technique to measure cross sections with LArTPCs. While moderately higher, our measurement of the ${\pi }^{-}$-Ar total hadronic cross section is generally in agreement with the geant4 prediction.

We present a paradox for evaporating black holes, which is common in most schemes trying to avoid the firewall by decoupling early and late radiation. At the late stage of the black hole evaporation, the decoupling between early and late radiation cannot be realized because the black hole has a very small coarse-grained entropy, then we are faced with the firewall again. We call the problem the hair-loss paradox as a pun on losing black hole soft hair during the black hole evaporation and the situation that the information paradox has put so much pressure on researchers.

Black holes in scalar-Gauss-Bonnet gravity are prone to scalarization, that is a spontaneous development of scalar hair for strong enough spacetime curvature. Since large spacetime curvature is associated with smaller black hole masses, the merging of black holes can lead to dynamical descalarization. This is a spontaneous release of the scalar hair of the newly formed black hole in case its mass is above the scalarization threshold. Depending on the exact form of the Gauss-Bonnet coupling function, the stable scalarized solutions can be either continuously connected to the Schwarzschild black hole, or the transitions between the two can happen with a jump. By performing simulations of black hole head-on collisions in scalar-Gauss-Bonnet gravity prone to dynamical descalization we have demonstrated that such a jump can be clearly observed in the accumulated gravitational wave data of multiple merger events with different masses. The simulations were performed in the decoupling limit approximation, where the backreaction of the scalar field on the metric is neglected. This is a reasonable assumption for weak enough scalar fields. The distinct signature in the gravitational wave signal will share similarities with the effects expected from first order matter phase transitions happening during neutron star binary mergers.

In the preceding paper of this series of articles we constructed the twisted geometry coherent states in all dimensional loop quantum gravity and established their peakedness properties. In this paper we establish the “Ehrenfest property” of these coherent states which are labeled by the twisted geometry parameters. By this we mean that the expectation values of the polynomials of the elementary operators as well as the operators which are not polynomial functions of the elementary operators, reproduce, to zeroth order in $\hslash$, the values of the corresponding classical functions at the twisted geometry space point where the coherent state is peaked.

The interpretation of semiclassical gravity as an ensemble-average of CFTs has provided much progress in understanding the factorization problem and the information paradox. In this article, we consider an averaging over boundary conditions in two-dimensional boundary conformal field theories (BCFTs). We show that the boundary averaging plays an important role not only in producing wormhole contributions but also in resolving the following problem. In general setups in AdS/BCFT, one can find unphysical solutions where branes have (self-)intersections. We show that the averaging nicely resolves this intersection problem. This provides another piece of evidence that averaging plays an important role in reproducing Einstein gravity. We also propose that the averaging provides a BCFT dual of the island model.

The causal structure is a quintessential element of continuum spacetime physics and needs to be properly encoded in a theory of Lorentzian quantum gravity. Established spin foam [and tensorial group field theory (TGFT)] models mostly work with relatively special classes of Lorentzian triangulations (e.g., built from spacelike tetrahedra only) obscuring the explicit implementation of the local causal structure at the microscopic level. We overcome this limitation and construct a full-fledged model for Lorentzian quantum geometry the building blocks of which include spacelike, lightlike, and timelike tetrahedra. We realize this within the context of the Barrett-Crane TGFT model. Following an explicit characterization of the amplitudes via methods of integral geometry and the ensuing clear identification of local causal structure, we analyze the model’s amplitudes with respect to its (space)time-orientation properties and provide also a more detailed comparison with the framework of causal dynamical triangulations.

We consider the Nielsen-Olesen vortex nonminimally coupled to Einstein gravity with a cosmological constant $\mathrm{\Lambda }$. A nonminimal coupling term $\xi R|\varphi {|}^2$ is natural to add to the vortex as it preserves gauge invariance (here $R$ is the Ricci scalar and $\xi$ a dimensionless coupling constant). This term plays a dual role: It contributes to the potential of the scalar field and to the Einstein-Hilbert term for gravity. As a consequence, the vacuum expectation value (VEV) of the scalar field and the cosmological constant in the ${\mathrm{AdS}}_3$ background depend on $\xi$. This leads to a novel feature: There is a critical coupling ${\xi }_c$ where the VEV is zero for $\xi \ge {\xi }_c$ but becomes nonzero when $\xi$ crosses below ${\xi }_c$ and the gauge symmetry is spontaneously broken. Moreover, we show that the VEV near the critical coupling has a power-law behavior proportional to $|\xi -{\xi }_c{|}^{1/2}$. Therefore, ${\xi }_c$ can be viewed as the analog of the critical temperature $T_c$ in Ginzburg-Landau (GL) mean-field theory where a second-order phase transition occurs below $T_c$ and the order parameter has a similar power-law behavior proportional to $|T-T_c{|}^{1/2}$ near $T_c$. The plot of the VEV as a function of $\xi$ shows a clear discontinuity in the slope at ${\xi }_c$ and looks similar to plots of the order parameter versus temperature in GL theory. The critical coupling exists only in an ${\mathrm{AdS}}_3$ background; it does not exist in asymptotically flat spacetime (topologically a cone) where the VEV remains at a fixed nonzero value independent of $\xi$. However, the deficit angle of the asymptotic conical spacetime depends on $\xi$ and is no longer determined solely by the mass; remarkably, a higher mass does not necessarily yield a higher deficit angle. The equations of motion are more complicated with the nonminimal coupling term present. However, via a convenient substitution, one can reduce the number of equations and solve them numerically to obtain exact vortex solutions.

We study a higher order conformally coupled scalar tensor theory endowed with a covariant geometric constraint relating the scalar curvature with the Gauss-Bonnet scalar. It is a particular Horndeski theory including a canonical kinetic term but without shift or parity symmetry for the scalar. The theory also stems from a Kaluza-Klein reduction of a well-defined higher dimensional metric theory. Properties of an asymptotically flat spherically symmetric black hole are analyzed, and new slowly rotating and radiating extensions are found. Through disformal transformations of the static configurations, gravitating monopolelike solutions and eternal wormholes are presented. The latter are shown to extract from spacetime possible naked singularities, yielding completely regular and asymptotically flat spacetimes.

We model the supermassive dark object $M87^{*}$ as a Schwarzschild lens and study the variations in tangential, radial, and total (the product of tangential and radial) magnifications of images (primary, secondary, and relativistic) against the changes in angular source position and the ratio of lens-source to the observer-source distance. Further, we study the behavior of partial derivatives (with respect to the angular source position) of total magnifications of images against the angular source position. Finally, we model supermassive dark objects at centers of 40 galaxies as Schwarzschild lenses and study the variations in tangential, radial, and total magnifications of images against the change in the ratio of mass of the lens to its distance. These studies yield many nonintuitive results which are likely to be significant for next generation Event Horizon Telescope observations. We hypothesize that there exists a distortion parameter such that its signed sum for all images of singular gravitational lensing of a source identically vanishes. We test this with images of Schwarzschild lensing in weak and strong gravitational fields and find that this esthetically appealing hypothesis succeeds with flying colors.