We derive loop quantum gravity corrections to the Raychaudhuri equation in the interior of a Schwarzschild black hole and near the classical singularity. We show that the resulting effective equation implies defocusing of geodesics due to the appearance of repulsive terms. This prevents the formation of conjugate points, renders the singularity theorems inapplicable, and leads to the resolution of the singularity for this spacetime.

We study the motion of particles in the background of a three-dimensional rotating Hořava anti–de Sitter black hole that corresponds to a Lorentz-violating version of the Bañados-Teitelboim-Zanelli (BTZ) black hole and we analyze the effect of the breaking of Lorentz invariance in such motion by solving analytically the geodesic equations. Mainly, we find that the Lorentz-violating version of the BTZ black hole possesses a more rich geodesic structure, where the planetary and circular orbits are allowed, which does not occur in the BTZ background.

We construct analytical initial data for a slowly moving and rotating black hole for generic orientations of the linear momentum and the spin. We solve the Hamiltonian constraint approximately and work out the properties of the apparent horizon and show the dependence of its shape on the angle between the spin and the linear momentum. In particular, a dimple, whose location depends on the mentioned angle, arises on the two-sphere geometry of the apparent horizon. We exclusively work in the case of conformally flat initial metrics.

Superradiant scattering of linear spin $s=0,\pm 1,\pm 2$ fields on Kerr black hole background is investigated in the time domain by integrating numerically the homogeneous Teukolsky master equation. The applied numerical setup has already been used in studying long time evolution and tail behavior of electromagnetic and metric perturbations on rotating black hole background [Phys. Rev. D 100, 104025 (2019)]. To have a clear setup the initial data is chosen to be of the compact support, while to optimize superradiance the frequency of the initial data is fine tuned. Our most important finding is that the rate of superradiance strongly depends on the relative position of the (compact) support of the initial data and the ergoregion. When they are well-separated then only a modest—in case of $s=0$ scalar fields negligible—superradiance occurs, whereas it can get to be amplified significantly whenever the support of the initial data and the ergoregion overlap.

In the context of $f(R)$ generalizations to the Holst action, endowed with a dynamical Immirzi field, we derive an analytic solution describing asymptotically anti–de Sitter black holes with hyperbolic horizon. These exhibit a scalar hair of the second kind, which ultimately depends on the Immirzi field radial behavior. In particular, we show how the Immirzi field modifies the usual entropy law associated to the black hole. We also verify that the Immirzi field boils down to a constant value in the asymptotic region, thus restoring the standard loop quantum gravity picture. We finally prove the violation of the reverse isoperimetric inequality, resulting in the superentropic nature of the black hole, and we discuss in detail the thermodynamic stability of the solution.

The kinetic Sunyaev-Zel’dovich (kSZ) effect is a secondary cosmic microwave background (CMB) anisotropy induced by the scattering of CMB photons off intervening electrons. Through cross-correlations with tracers of large-scale structure, the kSZ effect can be used to reconstruct the three-dimensional radial-velocity field, a technique known as kSZ tomography. We explore the cross-correlation between the CMB and line-intensity fluctuations to retrieve the late-time kSZ signal across a wide redshift range. We focus on the singly ionized carbon emission line and predict the signal-to-noise ratio of the kSZ tomography signal between redshifts $z=1–5$ for upcoming experiments. We show that, while instruments currently under construction may reach a low-significance detection of kSZ tomography, next-generation experiments will achieve greater sensitivity, with a detection significance of $\mathcal{O}({10}^2–{10}^3)$. Due to sample-variance cancellation, the cross-correlation between the reconstructed velocity field from kSZ tomography and intensity fluctuations can improve measurements of contributions from new physics to the power spectrum at large scales. To illustrate this improvement, we consider models of the early Universe that induce primordial local-type non-Gaussianity and correlated compensated isocurvature perturbations. We show that with CMB-S4 and an AtLAST-like survey, the uncertainty on $f_{\mathrm{NL}}$ and $A_{\mathrm{CIP}}$ can be reduced by a factor of approximately 3, achieving $\sigma (f_{\mathrm{NL}})\lesssim 1$. We further show that probing both low and high redshifts is crucial to break the degeneracy between the two parameters.

We investigate the production of primordial black holes and their contribution to the presently observed dark matter in a dilaton two-field extension of Starobinsky’s quadratic $f(R)$ model of inflation. The model features a multi-field amplification mechanism which leads to the generation of a sharp peak in the inflationary power spectrum at small wavelengths responsible for the production of primordial black holes. This mechanism is significantly different from single-field models and requires a stochastic treatment during an intermediate phase of the inflationary dynamics. We find that the model leads to a successful phase of effective single-field Starobinsky inflation for wavelengths probed by the cosmic microwave background radiation and explains the observed cold dark matter content in the Universe by the formation of primordial black holes.

A rapid phantom transition of the dark energy equation of state parameter $w$ at a transition redshift $z_t<0.1$ of the form $w(z)=-1+\mathrm{\Delta }w\mathrm{\Theta }(z_t-z)$ with $\mathrm{\Delta }w<0$ can lead to a higher value of the Hubble constant while closely mimicking a $\mathrm{Planck}18/\mathrm{\Lambda }\mathrm{CDM}$ form of the comoving distance $r(z)={\int }_0^z\frac{d{z}^{\prime }}{H(z^{\prime })}$ for $z>z_t$. Such a transition however would imply a significantly lower value of the SnIa absolute magnitude $M$ than the value $M_C$ imposed by local Cepheid calibrators at $z<0.01$. Thus, in order to resolve the $H_0$ tension it would need to be accompanied by a similar transition in the value of the SnIa absolute magnitude $M$ as $M(z)=M_C+\mathrm{\Delta }M\mathrm{\Theta }(z-z_t)$ with $\mathrm{\Delta }M<0$. This is a late $w-M$ phantom transition ($LwMPT$). It may be achieved by a sudden reduction of the value of the normalized effective Newton constant $\mu =G_{\mathrm{eff}}/G_{\mathrm{N}}$ by about 6% assuming that the absolute luminosity of SnIa is proportional to the Chandrasekhar mass which varies as ${\mu }^{-3/2}$. We demonstrate that such an ultra low $z$ abrupt feature of $w-M$ provides a better fit to cosmological data compared to smooth late time deformations of $H(z)$ that also address the Hubble tension. For $z_t=0.02$ we find $\mathrm{\Delta }w\simeq -4$, $\mathrm{\Delta }M\simeq -0.1$. This model also addresses the growth tension due to the predicted lower value of $\mu$ at $z>z_t$. A prior of $\mathrm{\Delta }w=0$ (no $w$ transition) can still resolve the $H_0$ tension with a larger amplitude $M$ transition with $\mathrm{\Delta }M\simeq -0.2$ at $z_t\simeq 0.01$. This implies a larger reduction of $\mu$ for $z>0.01$ (about 12%). The $LwMPT$ can be generically induced by a scalar field nonminimally coupled to gravity with no need of a screening mechanism since in this model $\mu =1$ at $z<0.01$.

The observed correlation between the far-infrared and radio luminosities of galaxies illustrates the close connection between star formation and cosmic-ray production. Intriguingly, recent gamma-ray observations indicate that recycled/millisecond pulsars (MSPs), which do not trace recent star formation, may also efficiently accelerate cosmic-ray electrons. We study the contribution of MSPs to the galactic nonthermal radio emission, finding that they can dominate the emission from massive quiescent galaxies. This model can explain recent LOFAR observations that found a peculiar radio excess in galaxies with high stellar masses and low star-formation rates. We show that MSP-based models provide a significantly improved fit to LOFAR data. We discuss the implications for the radio-far-infrared correlation, the observation of radio excesses in nearby galaxies, and local electron and positron observations.

Extending the quantum effective approach of Son and Nicolis and incorporating dissipation, we develop a Müller-Israel-Stewart (MIS) formalism for describing a superfluid out of equilibrium by including the Goldstone boson and the condensate together with the hydrodynamic modes as the effective degrees of freedom. We find that the evolution of the superfluid undergoing Bjorken flow is governed by the conventional hydrodynamic attractor with unbroken symmetry and an even number of novel nondissipative fixed points with broken symmetry. If the initial temperature is supercritical, then the condensate becomes exponentially small very rapidly, and the system is trapped by the hydrodynamic attractor for a long intermediate time before it reheats rapidly and switches to one of the symmetry-breaking fixed points eventually. Finally, we show that the fixed points are unstable against inhomogeneous perturbations that should lead to spinodal decomposition. We conclude that these features should be generic beyond the MIS formalism.

New light particles may be produced in large numbers in the far-forward region at the LHC and then decay to dark matter, which can be detected through its scattering in far-forward experiments. We consider the example of invisibly decaying dark photons, which decay to dark matter through $A^{\prime }\to \chi \chi$. The dark matter may then be detected through its scattering off electrons $\chi e^{-}\to \chi e^{-}$. We consider the discovery potential of detectors placed on the beam collision axis 480 m from the ATLAS interaction point, including an emulsion detector $(\mathrm{FASER}\nu 2)$ and, for the first time, a Forward Liquid Argon Experiment (FLArE). For each of these detector technologies, we devise cuts that effectively separate the single $e^{-}$ signal from the leading neutrino- and muon-induced backgrounds. We find that 10- to 100-tonne detectors may detect hundreds to thousands of dark matter events in the high-luminosity Large Hadron Collider (HL-LHC) era and will sensitively probe the thermal relic region of parameter space. These results motivate the construction of far-forward emulsion and liquid argon detectors at the LHC, as well as a suitable location to accommodate them, such as the proposed Forward Physics Facility.

We calculate the low-energy constant $L_{10}$ in a two-representation SU(4) lattice gauge theory that is close to a composite-Higgs model. From this we obtain the contribution of the new strong sector to the $S$ parameter. This leads to an upper bound on the vacuum misalignment parameter $\xi$ which is similar to current estimates of this bound. Our result agrees with large-$N_c$ scaling expectations, within large systematic uncertainties.

It is well known that a positive value of redshift drift is a signature of violation of the strong energy condition within general relativistic Friedmann-Lemaître-Robertson-Walker (FLRW) universe models. In the Lambda Cold Dark Matter ($\mathrm{\Lambda }\mathrm{CDM}$) paradigm of cosmology, founded on the FLRW model ansatz, the violation of the strong energy condition is realized by a dark energy component with “equation of state” equal to minus unity. This dark energy component, which is unexplained in the standard model of particle physics, facilitates the acceleration of cosmological length scales. Such an acceleration is needed to provide a consistent fit of the general relativistic FLRW universe models to available data. It remains a possibility that dark energy, and the associated violation of the strong energy condition, is an artefact of the FLRW model ansatz imposed for the interpretation of data, rather than due to a fundamental cosmological constant of nature. Here we show—without making assumptions on the metric tensor of the Universe—that redshift drift is a promising direct probe of violation of the strong energy condition within the theory of general relativity. We discuss our results in relation to upcoming Lyman-$\alpha$ forest measurements of redshift drift.

We do not observe quantum effects on cosmological scales. Thus, if loop quantum cosmology (LQC) is to provide an accurate depiction of the real world, it must allow for quantum states of spacetime geometry which are semiclassical in two respects: they must be sharply peaked around a single, classical geometry, and they must have small quantum fluctuations. It is generally assumed that Gaussian states exhibit both of these properties. After all, they do in ordinary quantum mechanics. In this paper, we derive exact closed-form expressions for the fluctuations of Gaussian states in LQC and their lower bound given by the Robertson-Schrödinger inequality. We demonstrate that, contrary to ordinary quantum mechanics, fluctuations for Gaussian states in spatially flat, homogeneous, and isotropic LQC diverge as the state variance increases (as well as in related cosmological models with the same kinematic Hilbert space and canonical observables). However, when the holonomy length is made to scale with a volume regularization parameter, these fluctuations may be arbitrarily suppressed by taking the fiducial volume to be large, providing analytic control over their divergence. Finally, we show that, despite this, Gaussian states in LQC generally do not minimize uncertainty. Moreover, it is conjectured that no such minimal-uncertainty states exist. Throughout this work, it becomes clear how important the often-assumed condition of holonomy length volume scaling is; we show that when this condition is violated, the resulting theory exhibits operator closure pathologies and other exotic algebraic features.

$S$-folds are a nonperturbative generalization of orientifold 3-planes which figure prominently in the construction of four-dimensional (4D) $\mathcal{N}=3$ superconformal field theories (SCFTs) and have also recently been used to realize examples of 4D $\mathcal{N}=2$ SCFTs. In this paper, we develop a general procedure for reading off the flavor symmetry experienced by D3-branes probing 7-branes in the presence of an $S$-fold. We develop an $S$-fold generalization of orientifold projection which applies to nonperturbative string junctions. This procedure leads to a different 4D flavor symmetry algebra depending on whether the $S$-fold supports discrete torsion. We also show that this same procedure allows us to read off admissible representations of the flavor symmetry in the associated 4D $\mathcal{N}=2$ SCFTs. Furthermore, this provides a prescription for how to define F-theory in the presence of $S$-folds with discrete torsion.

We find new exact solutions of the Abelian-Higgs model coupled to general relativity, characterized by a nonvanishing superconducting current. The solutions correspond to pp-waves, AdS waves, and Kundt spaces, for which both the Maxwell field and the gradient of the phase of the scalar are aligned with the null direction defining these spaces. In the Kundt family, the geometry of the two-dimensional surfaces orthogonal to the superconducting current is determined by the solutions of the two-dimensional Liouville equation, and in consequence, these surfaces are of constant curvature, as it occurs in a vacuum. The solution to the Liouville equation also acts as a potential for the Maxwell field, which we integrate into a closed-form. Using these results, we show that the combined effects of the gravitational and scalar interactions can confine the electromagnetic field within a bounded region in the surfaces transverse to the current.

Numerical simulations of binary black holes are accompanied by an initial spurious burst of gravitational radiation (called “junk radiation”) caused by a failure of the initial data to describe a snapshot of an inspiral that started at an infinite time in the past. A previous study showed that the superposed harmonic (SH) initial data give rise to significantly smaller junk radiation. However, it is difficult to construct SH initial data for black holes with dimensionless spin $\chi \gtrsim 0.7$. We here provide a class of spatial coordinate transformations that extend SH to higher spin. The new spatial coordinate system, which we refer to as superposed modified harmonic (SMH), is characterized by a continuous parameter—Kerr-Schild and harmonic spatial coordinates are only two special cases of this new gauge. We compare SMH with the superposed Kerr-Schild initial data by evolving several binary black hole systems with $\chi =0.8$ and 0.9. We find that the new initial data still lead to less junk radiation and only small changes of black hole parameters (e.g., mass and spin). We also find that the volume-weighted constraint violations for the new initial data converge with resolution during the junk stage $(t\lesssim 700M)$, which means there are fewer high-frequency components in waveforms at outer regions.

Although cosmic microwave background (CMB) is a critical component of cosmological probes of neutrino masses, it has trouble with local direct measurements of $H_0$, and this is called the $H_0$ tension. Since neutrino masses are correlated with $H_0$ in CMB, one can expect the cosmological bound on neutrino masses would be much affected by the $H_0$ tension. We investigate what impact this tension brings to the cosmological bound on neutrino masses by assuming a model with early recombination in the framework allowing a nonflat Universe which has been shown to resolve the tension. We argue that constraints on neutrino masses become significantly weaker in models where the $H_0$ tension can be resolved.