In this paper, we extend the treatment of asymptotically decelerating spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) spacetimes initiated in [M. E. Rojo and T. Heckelbacher, Phys. Rev. D 103, 064009 (2021).]. We show that a certain class of those metrics is ruled by the asymptotic algebra $\mathfrak{b}\mathfrak{m}{\mathfrak{s}}_s$, which belongs to a one-parameter family of deformations of $\mathfrak{b}\mathfrak{m}\mathfrak{s}$. Furthermore, we enlarge our ansatz to include $\text{Diff}(S^2)$ transformations whose asymptotic algebra $\mathfrak{g}\mathfrak{b}\mathfrak{m}{\mathfrak{s}}_s$ is a one-parameter deformation of $\mathfrak{g}\mathfrak{b}\mathfrak{m}\mathfrak{s}$. Therefore, the holographic algebras $\mathfrak{b}\mathfrak{m}{\mathfrak{s}}_s$ and $\mathfrak{g}\mathfrak{b}\mathfrak{m}{\mathfrak{s}}_s$ in FLRW can be related to their flat counterparts through a cosmological holographic flow. Finally, we introduce a logarithmic ansatz in order to account for cosmological black holes, which does not generally satisfy the peeling property but preserves the asymptotic algebra.

Recent strong-field regime tests of gravity are so far in agreement with general relativity. In particular, astrophysical black holes appear all to be consistent with the Kerr spacetime, but the statistical error on current observations allows for small yet detectable deviations from this description. Here we study superradiance of scalar and electromagnetic test fields around the Kerr-like Konoplya–Zhidenko black hole and we observe that for large values of the deformation parameter superradiance is highly suppressed with respect to the Kerr case. Surprisingly, there exists a range of small values of the deformation parameter for which the maximum amplification factor is larger than the Kerr one. We also provide a first result about the superradiant instability of these non-Kerr spacetimes against massive scalar fields.

Metric of axially symmetric asymptotically flat black holes in an arbitrary metric theory of gravity can be represented in the general form which depends on infinite number of parameters. We constrain this general class of metrics by requiring the existence of additional symmetries, which lead to the separation of variables in the Hamilton-Jacobi and Klein-Gordon equations, and show that once the metric functions change sufficiently moderately in some region near the black hole, the black-hole shadow depends on a few deformation parameters only. We analyze the influence of these parameters on the black-hole shadow. We also show that the shadow of the rotating black hole in the Einstein-dilaton-Gauss-Bonnet theory is well approximated if the terms violating the separation of variables are neglected in the metric.

We study a viable connection between the circular-equatorial orbits and reflection symmetry across the equatorial plane of a vacuum stationary axis-symmetric spacetime in general relativity. The behavior of the circular equatorial orbits in the direction perpendicular to the equatorial plane is studied, and different outcomes in the presence and in the absence of the reflection symmetry are discussed. We conclude that in the absence of the equatorial reflection symmetry neither stable nor unstable circular orbit can exist on the equatorial plane. Moreover, to address the observational aspects, we provide two possible examples relating gravitational wave astronomy and the thin accretion disk which can put constraints on the symmetry breaking parameters.

Light rings (LRs) play an important role in gravitational wave observations and black hole photographs. In this paper, we investigate general features of LRs in stationary, axisymmetric, asymptotically flat spacetimes with or without horizons. For a nonextremal black hole, we show explicitly that there always exist at least two LRs propagating in opposite directions, where the outermost one is radially unstable. For an extremal black hole, we show that there exists at least one retrograde LR. We find that there is at least one LR which is angularly stable. The stability analysis does not involve any energy condition. Our method also applies to horizonless spacetimes and we prove that LRs always appear in pairs. Only some natural and generic assumptions are used in our proof. The results are applicable to general relativity as well as most modified theories of gravity. In contrast to previous works on this issue, we obtain much stronger results with a much more straightforward approach.

Over 30 years ago, Barrow and Tipler proposed the principle according to which the action integrated over the entire four-manifold describing the universe should be finite. Here we explore the cosmological consequences of a related criterion, namely, that semiclassical transition amplitudes from the early universe up to current field values should be well defined. On a classical level, our criterion is weaker than the Barrow-Tipler principle, but it has the advantage of being sensitive to quantum effects. We find significant consequences for early universe models, in particular, eternal inflation and strictly cyclic universes are ruled out. Within general relativity, the first phase of evolution cannot be inflationary, and it can be ekpyrotic only if the scalar field potential is trustworthy over an infinite field range. Quadratic gravity eliminates all nonaccelerating backgrounds near a putative big bang (thus imposing favorable initial conditions for inflation), while the expected infinite series of higher-curvature quantum corrections eliminates Lorentzian big bang spacetimes altogether. The scenarios that work best with the principle of finite amplitudes are the no-boundary proposal, which gives finite amplitudes in all dynamical theories that we have studied, and string-inspired loitering phases. We also comment on the relationship of our proposal to the swampland conjectures.

We investigate clustering properties of dark matter halos and galaxies to search for optimal statistics and scales where possible departures from general relativity (GR) could be found. We use large $N$-body cosmological simulations to perform measurements based on the two-point correlation function (2PCF) in GR and in selected modified gravity (MG) structure formation scenarios. As a test bed, we employ two popular beyond-GR models: $f(R)$ gravity and the normal branch of the Dvali-Gabadadze-Porrati (nDGP) braneworld. We study a range of simulated halo and galaxy populations and reveal a noticeable MG signal in the monopole and quadrupole moments of the redshift-space 2PCF and in the so-called clustering wedges. However, once expressed in terms of the linear distortion parameter $\beta$, the statistical significance of these signals largely diminishes due to a strong degeneracy between MG-enhanced clustering and modified tracer bias. To circumvent this, we consider statistics less dependent on the bias: relative clustering ratios. We generalize the monopole ratio proposed in earlier work to multipole moments and clustering wedges and introduce a new estimator of the $\beta$ parameter. The clustering ratios we extract foster noticeable differences between MG and GR models, reaching a maximum deviation of 10% at $2\sigma$ significance for specific variants of $f(R)$ and the nDGP. We show that such departures could be measured for $\beta$ if nonlinear effects at intermediate scales are correctly modeled. Our study indicates that the clustering ratios give great promise to search for signatures of MG in the large-scale structure. We also find that the selection of an optimal tracer sample depends on a particular statistics and gravity model to be considered.

We investigate the cosmological stability of light bosonic dark matter carrying a tiny electric charge. In the wavelike regime of high occupation numbers, annihilation into gauge bosons can be drastically enhanced by parametric resonance. The millicharged particle can either be minimally coupled to photons, or its electromagnetic interaction can be mediated via kinetic mixing with a massless hidden photon. In the case of a direct coupling, current observational constraints on the millicharge are stronger than those arising from parametric resonance. For the (theoretically preferred) case of kinetic mixing, large regions of parameter space are affected by the parametric resonance, leading at least to a fragmentation of the dark matter field, if not its outright destruction.

We measure the Voronoi density probability distribution function (PDF) for both dark matter and halos in N-body simulations. For the dark matter, Voronoi densities represent the matter density field smoothed on a uniform mass scale, which approximates the Lagrangian density field. For halos, the Voronoi densities contain information about the local environment of each halo. We measure the halo virial masses, the total amount of dark matter within each halo Voronoi cell, and the halo Voronoi cell volumes, and we show how halo abundances depend on these three quantities. We then study the position-dependent Voronoi density PDF, measured within finite subregions of the Universe, using separate universe simulations. We demonstrate that the spatial variation of the position-dependent PDF is due to large-scale density fluctuations, indicating that the position-dependent PDF is a biased tracer of large-scale structure. We measure this bias for the dark matter, and interpret it as the bias of regions of the Lagrangian density field that are selected based on density. For the halos, this bias can be interpreted as a form of assembly bias. We present the mapping from late-time to early-time Voronoi density for each simulation dark matter particle, which is highly stochastic. We compare the median of this stochastic map with spherical collapse calculations and discuss challenges involved in modeling the evolution of the density field on these scales.

The present work studies one of Einstein’s alternative formulations based on the nonmetricity scalar $Q$ generalized as $f(Q)$ theory. More specifically, we consider the power-law form of $f(Q)$ gravity, i.e., $f(Q)=Q+\alpha Q^n$. Here, we analyze the behavior of the cosmological model at the background and perturbation level. Using the dynamical system analysis, at the background level, we find the effective evolution of the model is the same as that of the $\mathrm{\Lambda }\mathrm{CDM}$ for $|n|<1$. Interestingly, the geometric component of the theory solely determined the late-time acceleration of the Universe. We also examine the integrability of the model by employing the method of singularity analysis. In particular, we find the conditions under which field equations pass the Painlevé test and hence possess the Painlevé property. While the equations pass the Painlevé test in the presence of dust for any value of $n$, the test is valid after the addition of radiation fluid only for $n<1$. Finally, at the perturbation level, the behavior of matter growth index signifies a deviation of the model from the $\mathrm{\Lambda }\mathrm{CDM}$ even for $|n|<1$.

The energy budget of cosmological first-order phase transition is essential for the gravitational wave spectra. Most of the previous studies are based on the bag model with same sound velocity in the symmetric and broken phase. We study the energy budget and the corresponding gravitational wave spectra beyond the bag model, where the sound velocities could be different in the symmetric and broken phase. Taking the Higgs sextic effective model as a representative model, we calculate the sound velocities in different phase, the gravitational wave spectra, and the signal-to-noise ratio for different combinations of phase transition parameters beyond the bag model. We compare these new results with the ones obtained from the bag model. The proper sound velocities and phase transition parameters at the appropriate temperature are important to obtain more precise predictions.

We investigate the high temperature fate of four-dimensional gauge-Yukawa theories featuring short distance conformality of either interacting or noninteracting nature. The latter is known as complete asymptotic freedom and, as templates, we consider non-Abelian gauge theories featuring either two singlet scalars coupled to gauged fermions via Yukawa interactions or two gauged scalars with(out) fermions. For theories with interacting fixed points at short distance, known as asymptotically safe, we consider two calculable examples. Exploring the landscape of safe and free theories above we discover a class of complete asymptotically free theories for which symmetry breaks at arbitrary high temperatures. In its minimal form this class is constituted by a theory with two fundamental gauged scalars each gauged under an independent group.

We study bounds on a neutral component of a weak doublet scalar lepton. A typical example of such a particle is sneutrinos in supersymmetric models. Using constraints from invisible Higgs decays, we place a lower bound of approximately $\frac{m_h}{2}$. We recast a mono-$W/Z$ search with a hadronic vector-boson tag in order to bound parameter space in the sneutrino–charged slepton mass plane. We find a lower bound on sneutrinos in the range of 55–100 GeV in the $36{\mathrm{fb}}^{-1}$ data set depending on the mass of the charged component. We propose a sensitivity search in the hadronic mono-$W/Z$ channel for HL-LHC and discuss both the discovery potential in case an excess is seen and the exclusion limit assuming no excess is seen.

We perform a comprehensive study of the homogeneous finite modular group $A_5^{\prime }$ which is the double covering of $A_5$. The integral weight and level 5 modular forms have been constructed up to weight 6 and they are decomposed into the irreducible representations of $A_5^{\prime }$. Then we perform a systematical analysis of the $A_5^{\prime }$ modular models for lepton masses and mixing. The phenomenologically viable models with minimal number of free parameters and the results of fit are presented. We find out 15 models with 9 real free parameters which can accommodate the experimental data of lepton sector. After including generalized $CP$ symmetry, 9 viable models with 7 free parameters are found out. We apply $A_5^{\prime }$ modular symmetry to the quark sector, and a quark-lepton unification model is given. The framework of modular invariance is extended to include the rational weight modular forms of level 5. The ring of modular forms at level 5 can be generated by two algebraically independent weight $1/5$ modular forms denoted by $F_1(\tau )$ and $F_2(\tau )$. We give the expressions of the rational weight modular forms of level 5 up to weight 3 and arrange them into the irreducible multiplets of finite metaplectic group ${\tilde{\mathrm{\Gamma }}}_5\cong A_5^{\prime }\times Z_5$. A neutrino mass model with ${\tilde{\mathrm{\Gamma }}}_5$ modular symmetry is presented, and the phenomenological predictions of the model are analyzed numerically.

Boosted dark matter (BDM) is a well-motivated class of dark matter (DM) candidates in which a small component of DM is relativistic at the present time. We lay the foundation for BDM searches via hadronic interactions in large liquid-argon time-projection chambers (LArTPCs), such as the Deep Underground Neutrino Experiment (DUNE). We investigate BDM-nucleus scattering in detail by developing new event-generation techniques with a parameterized detector simulation. We study the discovery potential in a DUNE-like experiment using the low threshold and directionality of hadron detection in LArTPCs and compare with other experiments.

We present an exploratory lattice QCD investigation of the differences between the valence quark structure of the pion and its radial excitation $\pi (1300)$ in a fixed finite volume using the leading-twist factorization approach. We present evidences that the first pion excitation in our lattice computation is a single particle state that is likely to be the finite volume realization of $\pi (1300)$. An analysis with reasonable priors result in better estimates of the excited state PDF and the moments, wherein we find evidence that the radial excitation of pion correlates with an almost two-fold increase in the momentum fraction of valence quarks. This proof-of-principle work establishes the viability of future lattice computations incorporating larger operator basis that can resolve the structural changes accompanying hadronic excitation.

The chiral transition and crossover in strong magnetic fields with an anomalous magnetic moment (AMM) are investigated in the two-flavor Nambu–Jona-Lasinio model. The vacuum divergence and nonphysical oscillation are removed by employing a magnetic-field-independent regularization scheme. In addition to the inverse magnetic catalysis effect, the nonzero AMM will turn the chiral crossover into a first-order phase transition. These effects have been clearly demonstrated by the smooth and sharp peaks of the thermal susceptibility and the distinct behavior of the speed of sound. Magnetic catalysis with zero AMM could probably develop into inverse magnetic catalysis with nonzero AMM at both zero and finite chemical potentials.

The self-energies of the full set of flavor SU(3) octet and decuplet baryons are computed within a relativistic chiral effective theory framework. The leading nonanalytic chiral behavior is derived for the octet and decuplet masses, and a finite-range regularization consistent with Lorentz and gauge invariance is applied to account for the finite size of the baryons. Using a four-dimensional dipole form factor, the relative importance of various meson-baryon loop contributions to the self-energies is studied numerically as a function of the dipole range parameter and meson mass, and a comparison is made between the relativistic results and earlier approximations within the heavy baryon limit.

Evolution equations for leading-twist operators in high orders of perturbation theory can be restored from the spectrum of anomalous dimensions and the calculation of the special conformal anomaly at one order less using conformal symmetry of QCD at the Wilson-Fisher critical point at noninteger $d=4-2ϵ$ space-time dimensions. In this work, we generalize this technique to axial-vector operators. We calculate the corresponding three-loop evolution kernels in Larin’s scheme and derive explicit expressions for the finite renormalization kernel that describes the difference to the vector case to restore the conventional modified minimal subtraction scheme. The results are directly applicable to deeply virtual Compton scattering and the transition form factor ${\gamma }^{*}\gamma \to \pi$.

We construct the wave functions in the $q$-deformed 2D Yang-Mills theory that compute torus correlation functions of affine currents in the vertex operator algebra associated to a class of 4D $\mathcal{N}=2$ superconformal field theory. These wave functions are then shown to reduce to the topological correlators of a set of Coulomb branch operators in the $T[SU(N)]$ theory, from which those correlators in the 3D mirror dual of the 4D $T_N$ theories can be computed.