The recent observation of the shadow of the supermassive black hole M87*, located at the center of the M87 galaxy, by the Event Horizon Telescope Collaboration has opened up a new window to probe the strong gravity regime. In this paper, we explicitly demonstrate the consequences of this observation on brane world black holes, characterized by existence of a negative tidal charge. Our results based on three observables associated with the shadow, namely, angular diameter, deviation from circularity, and axis ratio reveal that the existence of a negative tidal charge is more favored, possibly marking a deviation from general relativity.

The scattering phase shifts are invariant under unitary transformations of the Hamiltonian. However, the numerical solution of the scattering problem that requires to discretize the continuum violates this phase-shift invariance among unitarily equivalent Hamiltonians. We extend a newly found prescription for the calculation of phase shifts which relies only on the eigenvalues of a relativistic equal-time Hamiltonian and its corresponding Chebyshev angle shift. We illustrate this procedure numerically considering $\pi \pi$, $\pi N$ and $NN$ elastic interactions which turns out to be competitive even for a small number of grid points.

At present, there are outstanding discrepancies between standard model predictions and measurements of the muon’s $g-2$ and several $B$-meson properties. We resolve these anomalies by considering a two-Higgs-doublet model extended to include leptoquarks and a dark Higgs boson $S$. The leptoquarks modify $B$-meson decays and also induce an $S\gamma \gamma$ coupling, which contributes to the muon’s $g-2$ through a Barr-Zee diagram. We show that, for TeV-scale leptoquarks and dark Higgs boson masses $m_S\sim 10–200\mathrm{MeV}$, a consistent resolution to all of the anomalies exists. The model predicts interesting new decays, such as $B\to K^{(*)}{e}^{+}{e}^{-}$, $B\to K^{(*)}\gamma \gamma$, $K\to \pi \gamma \gamma$, and $h\to \gamma \gamma \gamma \gamma$, with branching fractions not far below current bounds.

An axionlike particle (ALP) offers a new direction in electroweak baryogenesis because the periodic nature enables it to trigger a strong first-order phase transition insensitively to the decay constant $f$. For $f$ much above TeV, the ALP-induced electroweak phase transition is approximately described by adiabatic processes, distinguishing our scenario for electroweak baryogenesis from the conventional ones. We show that, coupled to the electroweak anomaly, the ALP can naturally realize spontaneous electroweak baryogenesis to solve the matter-antimatter asymmetry problem for $f$ in the range between about ${10}^5$ and ${10}^7\mathrm{GeV}$. In such an ALP window, the $CP$ violation for baryogenesis is totally free from the experimental constraints, especially from the recently improved limit on the electron electric dipole moment. Future searches for ALPs could probe our scenario while revealing the connection between electroweak symmetry breaking and baryogenesis.

We generalize our previous formulation of gauge-invariant $\mathcal{PT}$-symmetric field theories to include models with non-Abelian symmetries and discuss the extension to such models of the Englert-Brout-Higgs-Kibble mechanism for generating masses for vector bosons. As in the Abelian case, the non-Abelian gauge fields are coupled to nonconserved currents. We present a consistent scheme for gauge fixing, demonstrating Becchi-Rouet-Stora-Tyutin invariance, and show that the particle spectrum and interactions are gauge invariant. We exhibit the masses that gauge bosons in the simplest two-doublet $\mathrm{SU}(2)\times \mathrm{U}(1)$ model acquire when certain scalar fields develop vacuum expectation values: they and scalar masses depend quartically on the non-Hermitian mass parameter $\mu$. The bosonic mass spectrum differs substantially from that in a Hermitian two-doublet model. This non-Hermitian extension of the Standard Model opens a new direction for particle model building, with distinctive predictions to be explored further.

We study the discovery potential of the $cg\to tA\to tZH$ process at the LHC, where $A$ and $H$ are $CP$-odd and -even exotic scalars, respectively. The context is the general two Higgs doublet model, where $cg\to tA$ is induced by the flavor changing neutral Higgs coupling ${\rho }_{tc}$. We find that the process $cg\to tA\to tZH$ can be discovered for $m_A\sim 400\mathrm{GeV}$, but would likely require high luminosity running of the LHC. Such a discovery would shed light on the mechanism behind the observed baryon asymmetry of the Universe. We also study $cg\to tA\to tZh$, where $h$ is the observed 125 GeV scalar, but find it out of reach at the LHC.

We propose a two-loop induced radiative neutrino model with hidden gauged $U(1)$ symmetry, in which dark matter of Dirac fermions arises. The relic density gets a contribution from annihilation and semiannihilation due to a residual ${\mathbb{Z}}_3$ parity. After imposing the requirement of neutrino oscillation data and lepton flavor violation bounds, we find that semiannihilation plays a crucial role in order to satisfy the relic density constraint $0.117<\mathrm{\Omega }{h}^2<0.123$, by proceeding near either one of two deconstructive scalar resonances. Our numerical analysis demonstrates the allowed region for the DM-scalar coupling with the DM mass in (80, 400) GeV.

Renormalization group procedure for effective particles (RGPEP) is applied in terms of a second-order perturbative computation to an Abelian gauge theory, as an example of application worth studying on the way toward derivation of a dynamical connection between the spectroscopy of bound states and their parton-model picture in the front form of Hamiltonian dynamics. In addition to the ultraviolet transverse divergences that are handled using the RGPEP in previously known ways, the small-x divergences are handled by introducing a mass parameter and a third polarization state for gauge bosons using a mechanism analogous to spontaneous breaking of global gauge symmetry, in a special limit that simplifies the theory to Soper’s front form of massive QED. The resulting orders of magnitude of scales involved in the dynamics of effective constituents or partons in the simplified theory are identified for the fermion and boson mass counterterms, effective masses, and self-interactions, as well as for the Coulomb-like effective interactions in bound states of fermions. Computations in orders higher than second are mentioned but not described in this article.

By studying the infrared fixed point of an $\mathcal{N}=(0,2)$ Landau-Ginzburg model, we find an example of modular invariant partition function beyond the ADE classification. This stems from the fact that a part of the left-moving sector is a new conformal field theory which is a variant of the parafermion model with level twenty-five.

Some magnetic phenomena in correlated electron systems were recently shown to be described in the continuum limit by a class of sigma models with a target space interpolating between $S^3$ and $C{P}^1$. In this paper we study a generalization of such models with a target space given by a fiber bundle with a Grassmannian base space. The metric of our target space is shown to be left-symmetric which implies that it is fully parametrized by two constants: the first one—the conventional coupling constant—is responsible for the overall scale of the target space while the second constant $\kappa$ parametrizes the size of the fibers. In two dimensions these sigma models are perturbatively renormalizable. We calculate their $\beta$ functions to two loops and find the RG flow of the coupling constants. We calculate the two-point function in the UV limit, which has a power law dependence with an exponent dependent on the RG trajectory.

Manifolds endowed with torsion and nonmetricity are interesting both from the physical and the mathematical points of view. In this paper, we generalize some results presented in the literature. We study Einstein manifolds (i.e., manifolds whose symmetrized Ricci tensor is proportional to the metric) in $d$ dimensions with nonvanishing torsion that has both a trace and a traceless part, and analyze invariance under extended conformal transformations of the corresponding field equations. Then, we compare our results to the case of Einstein manifolds with zero torsion and nonvanishing nonmetricity, where the latter is given in terms of the Weyl vector (Einstein-Weyl spaces). We find that the trace part of the torsion can alternatively be interpreted as the trace part of the nonmetricity. The analysis is subsequently extended to Einstein spaces with both torsion and nonmetricity, where we also discuss the general setting in which the nonmetricity tensor has both a trace and a traceless part. Moreover, we consider and investigate actions involving scalar curvatures obtained from torsionful or nonmetric connections, analyzing their relations with other gravitational theories that appeared previously in the literature. In particular, we show that the Einstein-Cartan action and the scale invariant gravity (also known as conformal gravity) action describe the same dynamics. Then, we consider the Einstein-Hilbert action coupled to a three-form field strength and show that its equations of motion imply that the manifold is Einstein with totally antisymmetric torsion.

Type Ia supernova observations yield estimates of the luminosity distance, which includes not only the background luminosity distance, but also the fluctuation due to inhomogeneities in the Universe. These fluctuations are spatially correlated, hence limiting the cosmological information. In particular, the spatial correlation of the supernova host galaxies is a dominant source of the fluctuation in the luminosity distance measurements. Utilizing the recent theoretical framework that accurately quantifies the information contents accounting for the three-dimensional correlation of the observables on the past light cone, we compute the maximum cosmological information obtainable from idealized supernova surveys, where an infinite number of observations are made over the full sky without any systematic errors up to a maximum redshift $z_{\mathrm{m}}$. Here we consider two cosmological parameters ${\mathrm{\Omega }}_m$ and $w_0$ and show that the cosmological information contents are a lot more reduced than previously computed in literature. We discuss how these fundamental limits set by cosmic variance can be overcome.

We consider an inelastic dark matter model, in which a fermion is charged under a broken U(1) gauge symmetry, and introduce a tiny Majorana mass term to split the fermion into two states with the light one being a dark matter candidate. If the gauge boson is light, it can mediate both elastic and inelastic dark matter self-interactions in dark halos, leading to observational consequences. Using a numerical technique based on partial wave analysis, we accurately calculate the elastic and inelastic self-scattering cross sections. We assume a thermal freeze-out scenario and fix the gauge coupling constant using the relic density constraint. Then, we focus on six benchmark masses of dark matter, covering a wide range from 10 MeV to 160 GeV and map parameter regions where the elastic scattering cross section per unit mass is within $1{\mathrm{cm}}^2/\mathrm{g}-5{\mathrm{cm}}^2/\mathrm{g}$, favored to solve small-scale issues of cold dark matter. If the heavy state can decay to the light state and a massless species, the inelastic up-scattering process can cool the halo and lead to core collapse. Taking galaxies with evidence of dark matter density cores, we further derive constraints on the parameter space. For dark matter masses below 10 GeV, the mass splitting must be large enough to forbid up scattering in the dwarf halo for evading the core-collapse constraint; while for higher masses, the up-scattering process can still be allowed. Our results show astrophysical observations can provide powerful tests for dark matter models with large elastic and inelastic self-interactions.

In contrast to the original type I seesaw mechanism that requires right-handed Majorana neutrinos at energies much higher than the electroweak scale, the so-called low scale seesaw models allow lighter masses for the additional neutrinos. Here we propose an alternative low scale type I seesaw model, where neither linear nor inverse seesaw mechanisms take place, but the spontaneous breaking of a discrete symmetry at an energy scale much lower than the model cutoff is responsible for the smallness of the light active neutrino masses. In this scenario, the model is defined with minimal particle content, where the right-handed Majorana neutrinos can have masses at the $\sim 50\mathrm{GeV}$ scale. The model is predictive in the neutrino sector having only four effective parameters that allow to successfully reproduce the experimental values of the six low energy neutrino observables.

The radiative type-I seesaw has been already implemented to explain the lightness of Majorana neutrinos with both Majorana and Dirac heavy fermions, and the lightness of Dirac neutrinos with Dirac heavy fermions. In this work, we present a minimal implementation of the radiative type-I seesaw with light Dirac neutrinos and heavy Majorana fermions. An inert doublet and a complex singlet scalar complete the dark sector, which is protected by an Abelian fermiophobic gauge symmetry that also forbids tree level mass contributions for the full set of light neutrinos. A fermion vectorlike extension of the model is also proposed where the light right-handed neutrinos can thermalize in the primordial plasma and the extra gauge boson can be directly produced at colliders. In particular, the current upper bound on $\mathrm{\Delta }{N}_{\mathrm{eff}}$ reported by PLANCK points to large ratios of $M_{Z^{\prime }}/g^{\prime }\gtrsim 40\mathrm{TeV}$, which can be competitive with collider constraint for $g^{\prime }$ sufficiently large in the ballpark of the Standard Model values, while future cosmic microwave background experiments may probe all the no minimal models presented here.

We propose a new class of infrared-collinear and Sudakov safe observables with an associated jet grooming technique that removes dynamically soft and large angle branches. It is based on identifying the hardest branch in the Cambridge/Aachen reclustering sequence and discarding prior splittings that occur at larger angles. This leads to a dynamically generated cutoff on the phase space of the tagged splitting that is encoded in a Sudakov form factor. In this exploratory study we focus on the mass and momentum sharing distributions of the tagged splitting which we analyze analytically to modified leading-logarithmic accuracy and compare to Monte Carlo simulations.

We propose a candidate $c$-function in arbitrary dimensional quantum field theories with broken Lorentz and rotational symmetry. For holographic theories we derive the necessary and sufficient conditions on the geometric background for these $c$-functions to satisfy the $c$-theorem. We obtain the null energy conditions for anisotropic background to show that they do not themselves assure the $c$-theorem. By employing them, we find that it is possible to impose conditions on the UV data that are enough to guarantee at least one monotonic $c$-function along the RG flow. These UV conditions can be used as building blocks for the construction of anisotropic monotonic RG flows. Finally, we apply our results to several known anisotropic theories and identify the region in the parameter space of the metric where the $c$-theorem holds for our proposed $c$-function.

We investigate the holographic complexity growth rate of a conformal field theory in a Friedman-Lemaître-Roberstson-Walker (FLRW) universe. We consider two ways to realize an FLRW spacetime from an anti–de Sitter Schwarzschild geometry. The first one is obtained by introducing a new foliation of the Schwarzschild geometry such that the conformal boundary takes the FLRW form. The other one is to consider a brane universe moving in the Schwarzschild background. For each case, we compute the complexity growth rate in a closed universe and a flat universe by using both the complexity-volume and complexity-action dualities. We find that there are two kinds of contributions to the growth rate: one is from the interaction among the degrees of freedom, while the other one from the change of the spatial volume of the universe. The behaviors of the growth rate depend on the details to realize the FLRW universe as well as the holographic conjecture for the complexity. For the realization of the FLRW universe on the asymptotic boundary, the leading divergent term for the complexity growth rate obeys a volume law which is natural from the field theory viewpoint. For the brane universe scenario, the complexity-volume and complexity-action conjectures give different results for the closed universe case. A possible explanation of the inconsistency when the brane crosses the black hole horizon is given based on the Lloyd bound.

In this paper, we study the thermodynamic geometry of charged Gauss-Bonnet black holes (and Reissner-Nordström black holes, for the sake of comparison) in anti–de Sitter spacetimes in both ($T$, $V$) and ($S$, $P$) planes. The thermodynamic phase space is known to have an underlying contact and metric structure; Ruppeiner geometry then naturally arises in this framework. Sign of Ruppeiner curvature can be used to probe the nature of interactions between the black hole microstructures. It is found that there are both attraction and repulsion dominated regions which are in general determined by the electric charge, Gauss-Bonnet coupling, and horizon radius of the black hole. The results are physically explained by considering that these black hole systems consist of charged as well as neutral microstructures much like a binary mixture of fluids.

In this article we explore the holographic duals of tensor models using collective field theory. We develop a description of the gauge invariant variables of the tensor model. This is then used to develop a collective field theory description of the dynamics. We consider matrixlike subsectors that develop an extra holographic dimension. In particular, we develop the collective field theory for the matrixlike sector of an interacting tensor model. We check the correctness of the large $N$ collective field by showing that it reproduces the perturbative expansion of large $N$ expectation values. In contrast to this, we argue that melonic large $N$ limits do not develop an extra dimension. This conclusion follows from the large $N$ value for the melonic collective field, which has delta function support. The finite $N$ physics of the model is also developed and nonperturbative effects in the $1/N$ expansion are exhibited.