We discuss $c$ functions and their holographic counterpart for two-dimensional field theories with Carrollian conformal fixed points in the UV and the IR. Specifically, we construct asymptotically flat domain wall solutions of three-dimensional Einstein-dilaton gravity that model holographic renormalization group (RG) flows between ${\mathrm{BMS}}_3$ invariant UV and IR fixed points. We prove three theorems for such flows: (1) for every holographic RG flow in ${\mathrm{AdS}}_3$, there is a corresponding one in flat space, (2) the BMS central charge in the UV cannot be smaller than in the IR, and (3) the UV/IR ratio of Virasoro central charges is identical to the UV/IR ratio of corresponding BMS central charges. Finally, we tentatively propose a Casini–Huerta-like $c$ functions for ${\mathrm{BMS}}_3$-invariant quantum field theories, inspired by the ${\mathrm{AdS}}_3/{\mathrm{CFT}}_2$ relation between monotonicity of the $c$ function and the quantum null energy condition.

We construct two families of ${\mathrm{AdS}}_2$ vacua in type IIB supergravity performing U(1) and SL(2) $T$-dualities on the ${\mathrm{AdS}}_3\times {\widehat{\mathbb{C}\mathbb{P}}}^3\times \mathrm{I}$ solutions to type IIA recently reported in [N. T. Macpherson and A. Ramirez, J. High Energy Phys. 08 (2023) 024]. Depending on the $T$-duality we operate, we find two different classes of solutions of the type ${\mathrm{AdS}}_2\times {\widehat{\mathbb{C}\mathbb{P}}}^3\times \mathrm{I}\times \mathrm{I}$ and ${\mathrm{AdS}}_3\times {\widehat{\mathbb{C}\mathbb{P}}}^3\times \mathrm{I}\times {\mathrm{S}}^1$. This provides evidence for more general classes of solutions ${\mathrm{AdS}}_2\times {\widehat{\mathbb{C}\mathbb{P}}}^3\times \mathrm{\Sigma }$, dual to superconformal quantum mechanics with $\mathcal{N}=5,6$ supersymmetry.

We provide a group theory approach to coherent states describing quantum space-time and its properties. This provides a relativistic framework for the metric of a Riemmanian space with bosonic and fermionic coordinates, its continuum and discrete states, and a kind of “quantum optics” for the space-time. New results of this paper are: (i) The space-time is described as a physical coherent state of the complete covering of the SL(2C) group, e.g., the metaplectic group Mp(n). (ii) (The discrete structure arises from its two irreducible even $(2n)$ and odd ($2n+1$) representations, ($n=1,2,3\dots$), spanning the complete Hilbert space $\mathcal{H}={\mathcal{H}}_{\mathrm{odd}}\oplus {\mathcal{H}}_{\mathrm{even}}$. Such a global or complete covering guarantees the CPT symmetry and unitarity. Large $n$ yields the classical and continuum manifold, as it must be. (iii) The coherent and squeezed states and Wigner functions of quantum-space-time for black holes and de Sitter, and (iv) for the quantum space-imaginary time (instantons), black holes in particular. They encompass the semiclassical space-time behavior plus high quantum phase oscillations, and notably account for the classical–quantum gravity duality and trans-Planckian domain. The Planck scale consistently corresponds to the coherent state eigenvalue $\alpha =0$ (and to the $n=0$ level in the discrete representation). It is remarkable the power of coherent states in describing both continuum and discrete space-time. The quantum space-time description is regular, there is no any space-time singularity here, as it must be.

We study the accretion of relativistic Vlasov gas onto a Kerr black hole, regarding the particles as distributed throughout all of the space, rather than just in the equatorial plane. We solve the relativistic Liouville equation in the full $3+1$-dimensional framework of Kerr geometry. For the stationary and axially symmetric flow, we prove that the distribution function is independent of the conjugate coordinates. For an explicit distribution that can be approximated as a Maxwell-Jüttner distribution, we further calculate the particle current density, stress-energy-momentum tensor, and unit accretion rates of mass, energy, and angular momentum. The analytic results at large distance are shown to be consistent with the limits of the numerical ones computed at finite distance. In particular, we show that the unit mass accretion rate agrees with the Schwarzschild result in the case of the low-temperature limit. Furthermore, we find from the numerical results that the three unit accretion rates vary with the angle in the Kerr metric and the accretion of Vlasov gas would slow down the Kerr black hole. The closer to the equator, the faster it slows down the black hole.

The precise tuning required to observe critical phenomena in gravitational collapse poses a challenge for most numerical codes. First, threshold estimation searches may be obstructed by the appearance of coordinate singularities, indicating the need for a better gauge choice. Second, the constraint violations to which simulations are susceptible may be too large and force searches to terminate prematurely. This is a particularly serious issue for first-order formulations. We want our adaptive pseudospectral code bamps to be a robust tool for the study of critical phenomena so, having encountered both of these difficulties in work on the vacuum setting, we turn here to investigate these issues in the classic context of a spherically symmetric massless scalar field. We suggest two general improvements. We propose a necessary condition for a gauge choice to respect discrete self-similarity (DSS). The condition is not restricted to spherical symmetry and could be verified with any $3+1$ formulation. After evaluating common gauge choices against this condition, we suggest a DSS-compatible gauge source function in generalized harmonic gauge (GHG). To control constraint violations, we modify the constraint damping parameters of GHG, adapting them to collapse spacetimes. This allows us to improve our tuning of the critical amplitude for several families of initial data, even going from 6 up to 11 digits. This is the most precise tuning achieved with the first-order GHG formulation to date. Consequently, we are able to reproduce the well-known critical phenomena as well as competing formulations and methods, clearly observing up to three echoes.

In sonic models of special relativity, the fact that the sonic medium violates (ordinary) Lorentz symmetry is apparent to observers external to the sonic medium but not to a class of observers existing within the medium itself. We show that the situation is symmetric: internal observers will judge physics in the external laboratory to violate their own sonic Lorentz symmetries. We therefore treat all observers on an equal footing such that each is able to retain a commitment to their own Lorentz symmetries. We then generalize beyond the case of subsystem-environment decompositions to situations in which there exist multiple phonon fields, all obeying Lorentz symmetries but with different invariant speeds. In such cases, we argue that all observers have freedom to choose which field is symmetry preserving, and so—in a certain precise sense—which other fields are perceived as having an “ether.” This choice is influenced, but not determined, by a desire for simplicity in the description of physical laws. Sending information faster than sound serves as a model of tachyonic signaling to a distant receiver. Immutable causality of the laboratory setup when perceived externally to a sonic medium manifests internally through the confinement of the tachyons to an apparent ether (with a rest frame), which we call a “tachyonic medium,” thereby preventing tachyonic exchange from emulating the scenario of a round-trip signal traveling into an observer’s past causal cone. The assignment of sonic-Lorentz-violating effects to fields that obey “photonic” Lorentz symmetries thus ensures that causality associated with the “sonic” Lorentz symmetries is preserved.

In astronomy, gravitational lensing of light leads to the formation of multiple images, arcs, Einstein rings, and, most important, the shadow of black holes. Analogously in the vicinity of a massive compact object massive particles, following timelike geodesics, are gravitationally lensed. So far gravitational lensing of massive particles was mainly investigated in the weak and strong field limits. In this paper we will, for the first time, investigate exact gravitational lensing of massive particles using the example of the charged Newman-Unti-Tamburino (NUT) metric (and its special cases) which contains three physical parameters, the mass parameter $m$, the electric charge $e$, and the gravitomagnetic charge $n$. We will first discuss and solve the equations of motion for unbound timelike geodesics using elementary and Jacobi’s elliptic functions and Legendre’s elliptic integrals. Then we will introduce an orthonormal tetrad to relate the $z$ component of the angular momentum and the Carter constant to the energy $E$ of the particles along the timelike geodesics and latitude-longitude coordinates on the celestial sphere of a stationary observer in the domain of outer communication. We will use these relations to derive the angular radius of the particle shadow of the black hole, to formulate an exact lens equation, and to derive the travel time of the particles in terms of the time coordinate and the proper time. Finally, we will discuss the impact of the physical parameters and the energy of the particles on observable lensing features. We will also comment on how we can use these features alone and in a multimessenger context together with the corresponding features for light rays to determine if an astrophysical black hole can be described by the charged NUT metric or one of its special cases.

Models that address both the Hubble and $S_8$ tensions with the same mechanism generically cause a prerecombination suppression of the small scale matter power spectrum. Here we focus on two such models. Both models introduce a self-interacting dark radiation fluid scattering with dark matter, which has a step in its abundance around some transition redshift. In one model, the interaction is weak and with all of the dark matter whereas in the other it is strong but with only a fraction of the dark matter. The weakly interacting case is able to address both tensions simultaneously and provide a good fit to a the Planck measurements of the cosmic microwave background (CMB), the Pantheon Type Ia supernovae, and a combination of low and high redshift baryon acoustic oscillation data, whereas the strongly interacting model cannot significantly ease both tensions simultaneously. The addition of high-resolution CMB measurements (ACT DR4 and SPT-3G) slightly limits both model’s ability to address the Hubble tension. The use of the effective field theory of large-scale structures analysis of BOSS DR12 LRG and eBOSS DR16 QSO data additionally limits their ability to address the $S_8$ tension. We explore how these models respond to these datasets in detail in order to draw general conclusions about what is required for a mechanism to address both tensions. We find that in order to fit the CMB data the time dependence of the suppression of the matter power spectrum plays a central role.

It is well known that, during inflation, the conformal invariance of the electromagnetic action has to be broken in order to produce magnetic fields of strengths observed today. Often, to further enhance the strengths of the magnetic fields, parity is also assumed to be violated when the fields are being generated. In this work, we examine the evolution of the quantum state of the Fourier modes of the nonconformally coupled and parity-violating electromagnetic field during inflation. We utilize tools such as the Wigner ellipse, squeezing parameters and quantum discord to understand the evolution of the field. We show that the violation of parity leads to an enhancement of the squeezing amplitude and the quantum discord (or, equivalently, in this context, the entanglement entropy) associated with a pair of opposite wave vectors for one of the two states of polarization (and a suppression for the other state of polarization), when compared to the case wherein parity is conserved. We highlight the similarities between the evolution of the Fourier modes of the electromagnetic field when parity is violated during inflation and the behavior of the modes of a charged, quantum, scalar field in the presence of a constant electric field in a de Sitter universe. We briefly discuss the implications of the results we obtain.

The neutrinos in the diffuse supernova neutrino background (DSNB) travel over cosmological distances and this provides them with an excellent opportunity to interact with dark relics. We show that a cosmologically significant relic population of keV-mass sterile neutrinos with strong self-interactions could imprint their presence in the DSNB. The signatures of the self-interactions would be “dips” in the otherwise smooth DSNB spectrum. Upcoming large-scale neutrino detectors, for example Hyper-Kamiokande, have a good chance of detecting the DSNB and these dips. If no dips are detected, this method serves as an independent constraint on the sterile neutrino self-interaction strength and mixing with active neutrinos. We show that relic sterile neutrino parameters that evade x-ray and structure bounds may nevertheless be testable by future detectors like TRISTAN, but may also produce dips in the DSNB which could be detectable. Such a detection would suggest the existence of a cosmologically significant, strongly self-interacting sterile neutrino background, likely embedded in a richer dark sector.

Neutrino gases are expected to form in high-density astrophysical environments, and accurately modeling their flavor evolution is critical to understanding such environments. In this work, we study a simplified model of such a dense neutrino gas in the regime for which neutrino-neutrino coherent forward scattering is the dominant mechanism contributing to the flavor evolution. We show evidence that the generic potential induced by this effect is nonintegrable and that the statistics of its energy level spaces are in good agreement with the Wigner surmise. We also find that individual neutrinos rapidly entangle with all of the others present, which results in an equilibration of the flavor content of individual neutrinos. We show that the average neutrino flavor content can be predicted utilizing a thermodynamic partition function. A random phase approximation to the evolution gives a simple picture of this equilibration. In the case of neutrinos and antineutrinos, processes like ${\nu }_e{\overline{\nu }}_e\leftrightarrows {\nu }_{\mu }{\overline{\nu }}_{\mu }$ yield a rapid equilibrium satisfying $n({\nu }_e)n({\overline{\nu }}_e)=n({\nu }_{\mu })n({\overline{\nu }}_{\mu })=n({\nu }_{\tau })n({\overline{\nu }}_{\tau })$ in addition to the standard lepton number conservation in regimes where off-diagonal vacuum oscillations are small compared to $\nu -\nu$ interactions.

The Einstein Telescope (ET) is a third-generation gravitational wave detector that includes a room-temperature high-frequency (ET-HF) and a cryogenic low-frequency laser interferometer (ET-LF). The cryogenic ET-LF is crucial for exploiting the full scientific potential of the ET. We present a new baseline design for the cryogenic payload that is thermally and mechanically consistent and compatible with the design sensitivity curve of the ET. The design includes two options for the heat extraction from the marionette, based on a monocrystalline high-conductivity marionette suspension fiber and a thin-wall titanium tube filled with static He-II. Following a detailed description of the design options and the suspension thermal noise (STN) modeling, we present the sensitivity curves of the two baseline designs, discuss the influence of various design parameters on the sensitivity of ET-LF, and conclude with an outlook to future R&D activities.

Gravitational-wave observatories become more sensitive with each observing run, increasing the number of detected gravitational-wave signals. A limiting factor in identifying these signals is the presence of transient non-Gaussian noise, which generates glitches that can mimic gravitational-wave signals. Our work provides a quasiphysical model waveform for the four most common types of short transient glitches, which are particularly problematic in the search for high-mass black hole binaries. Our model has only a few, physically interpretable parameters: central frequency, bandwidth, phase, amplitude, and time. We demonstrate the accuracy of our glitch template by fitting and removing a large sample of glitches from a month of LIGO and Virgo data from the O3 observing run. We can effectively remove three of the four types of short transients. We finally map the ability of these glitches to mimic binary black hole signals.

We compute the structure function, transverse momentum dependent parton distributions (TMDs), and generalized parton distributions (GPDs) for the photon from the light-front quantum electrodynamics (QED) Hamiltonian, determined for its constituent bare photon and electron-positron Fock components within the basis light-front quantization framework. While the structure function and GPDs align well with expectations, some oscillatory behavior in the TMDs emerges as a finite-basis artifact. We also compute the GPD and the corresponding structure function for the longitudinal polarization mode of the massive photon. We further study the photon mass dependence of the calculated observables. After performing nonperturbative renormalization, we obtain a good quality description of the perturbative QED properties of the photon, as well as good agreement with the experimental data for the massless photon’s structure function.

We study the impact of renormalization group effects on QCD axion phenomenology. Focusing on the Dine-Fischler-Srednicki-Zhitnitsky model, we argue that the relevance of running effects for the axion couplings crucially depends on the scale where the heavier Higgs scalars are integrated out. We study the impact of these effects on astrophysical and cosmological bounds as well as on the sensitivity of helioscopes experiments such as IAXO and XENONnT, showing that they can be sizable even in the most conservative case in which the two Higgs doublets remain as light as the TeV scale. We provide simple analytical expressions that accurately fit the numerical solutions of the renormalization group equations as a function of the mass scale of the heavy scalars.

The success of analytic waveform modeling within the effective-one-body (EOB) approach relies on the precise understanding of the physical importance of each technical element included in the model. The urgency of constructing progressively more sophisticated and complete waveform models (e.g. including spin precession and eccentricity) partly defocused the research from a careful comprehension of each building block (e.g. Hamiltonian, radiation reaction, ringdown attachment). Here we go back to the spirit of the first EOB works. We focus first on nonspinning, quasicircular, black hole binaries and analyze systematically the mutual synergy between numerical relativity (NR) informed functions and the high post-Newtonian corrections (up to 5PN) to the EOB potentials. Our main finding is that it is essential to correctly control the noncircular part of the dynamics during the late plunge up to merger. When this happens, either using NR-informed nonquasicircular corrections to the waveform (and flux) or high-PN corrections in the radial EOB potentials $(D,Q)$, it is easy to obtain $\mathrm{EOB}/\mathrm{NR}$ unfaithfulness $\sim {10}^{-4}$ with the noise of either Advanced LIGO or 3G detectors. We then improve the teobresums-giotto waveform model (dubbed teobresumsv4.3.2) for quasicircular, spin-aligned black hole binaries. We obtain maximal $\mathrm{EOB}/\mathrm{NR}$ unfaithfulness ${\overline{\mathcal{F}}}_{\mathrm{EOBNR}}^{\max }\sim {10}^{-3}$ (with Advanced LIGO noise and in the total mass range $10–200M_{\odot }$) for the dominant $\ell =m=2$ mode all over the 534 spin-aligned configurations available through the Simulating eXtreme Spacetime catalog. The model performance, also including higher modes, is then explored using the NR surrogates nrhybsur3dq8 and nrhybsur2dq15, to validate teobresumsv4.3.2 up to mass ratio $m_1/m_2=15$. We find that, over the set of configurations considered, more than 98% of the total-mass-maximized unfaithfulness lie below the 3% threshold when comparing to the surrogate models.

The second postulate of special relativity states that the speed of light in vacuum is independent of the emitter’s motion. The test of this postulate so far remains unexplored for gravitational radiation. We analyze data from the LIGO-Virgo detectors to test this postulate within the ambit of a model where the speed of the emitted GWs ($c^{\prime }$) from a binary depends on a characteristic velocity $\tilde{v}$ proportional to that of the reduced one-body system as $c^{\prime }=c+k\tilde{v}$, where $k$ is a constant. We have estimated the upper bound on the 90% credible interval over $k$ to be $k\le 8.3\times {10}^{-18}$, which is several orders of magnitude more stringent compared to previous bounds obtained from electromagnetic observations. The Bayes’ factor supports the second postulate with a strong evidence that the data is consistent with the null hypothesis $k=0$, upholding the principle of relativity for gravitational interactions.

Highly accurate models of the gravitational wave signal from coalescing compact binaries are built by completing analytical computations of the binary dynamics with nonperturbative information from numerical relativity (NR) simulations. In this paper we present four sets of NR simulations of equal-mass black hole binaries that undergo strong-field scattering: (i) we reproduce and extend the nonspinning simulations first presented in [Damour et al., Strong-field scattering of two black holes: Numerics versus analytics, Phys. Rev. D 89, 081503 (2014).]; (ii) we compute two suites of nonspinning simulations at higher energies, probing stronger field interactions; (iii) we present a series of spinning simulations including, for the first time, unequal-spin configurations. When comparing the NR scattering angles to analytical predictions based on state-of-the-art post-Minkowskian (PM) calculations, we find that PM-expanded scattering angles show poor convergence towards NR data. By contrast, a resummed computation of scattering angles via a spin-dependent, radiation-reacted, effective-one-body potential shows excellent agreement for both nonspinning and spinning configurations.