Working in a semiclassical setting, we consider solutions of the Einstein equations that exhibit light trapping in finite time according to distant observers. In spherical symmetry, we construct near-horizon quantities from the assumption of regularity of the renormalized expectation value of the energy-momentum tensor, and derive explicit coordinate transformations in the near-horizon region. We examine the boundary conditions appropriate for embedding the model into a cosmological background, describe their evaporation in the linear regime and highlight the observational consequences, while also discussing the implications for the laws of black hole mechanics.

A modification of general relativity that is based on the gravitational standard-model extension and incorporates nondynamical background fields has recently been studied via the ADM formalism. Our objective in this paper is to develop a better understanding of the additional contributions that arise on the spacetime boundary $\partial \mathcal{M}$. An extension of the previously introduced boundary terms, which are relevant in the context of asymptotically flat spacetimes, follows from the decomposition of $\partial \mathcal{M}$ into timelike and spacelike hypersurfaces. Furthermore, we present an alternative method of deriving the field equations satisfied by the induced metric on the purely spacelike hypersurfaces of the foliated spacetime. This leads to the dynamical part of the Einstein equations modified by the background fields. Our results have the potential to be applicable in various contexts such as modified black holes and cosmology.

We investigate the production process of induced gravity waves due to large scalar fluctuations in the paradigm of quintessential inflation. We numerically solve the Mukhanov-Sasaki equation for different sets of parameters to obtain the power spectra. We demonstrate that the induced gravity wave signal generated in this framework can fall within the region of the NANOGrav data for chosen values of model parameters. We show that there is an allowed region of parameter space where the effect shifts to the high-frequency regime relevant to the Laser Interferometer Space Antenna and other available sensitivities.

The Universe at the present epoch is found to be a network of matter overdense and underdense regions. Usually, the overdense regions are dominated by the dark-matter (DM) filaments where massive gravitationally bound structures such as groups and clusters of galaxies form at the nodes. At the cosmological timescales, the baryonic matter follows the flow of DM only, and together they form the cosmic web. To date, this picture of the Universe is best revealed through cosmological large-volume simulations and large-scale galaxy redshift surveys, in which, the most important step is the appropriate identification of structures. So far, these structures are identified using various group finding codes, mostly based on the friend of friends (FoF) or spherical overdensity (SO) algorithms. Although, the main purpose is to identify gravitationally bound structures, surprisingly, the mass information has hardly been used effectively by these codes. Moreover, while it is an established fact that the bound structures can best be formed at some particular mass overdense regions and practically the large-scale structures are barely spherical in shape, the methods used so far either constrain the overdensity or use the real unstructured geometry only. Even though these are key factors in the accurate determination of structures-mass information that can precisely constrain the cosmological models of the Universe, hardly any attempt has been made as yet to consider these important parameters together while formulating the grouping algorithms. In this paper, we present our proposed algorithm called the measure of increased tie with gravity order which takes care of all the above-mentioned relevant features and ensures the bound structures by means of physical quantities, mainly mass and the total energy information. Unlike the usual FoF method where a statistically chosen single linking length is used for all grouping elements, we introduced a novel concept of physically relevant arm length for each element depending on their individual gravity leading to a distinct linking length for each unique pair of elements. This proposed algorithm is thus fundamentally new such that, not only able to catch the gravitationally bound, real unstructured geometry very well, it does identify it roughly within a predefined physically motivated density threshold. Such a thing could not be simultaneously achieved before by any of the usual FoF or SO-based methods. We also demonstrate the unique ability of the code in the appropriate identification of structures, both from large volume cosmological simulations as well as from galaxy redshift surveys, highlighting the fact that it mitigates a few shortcomings of the basic FoF and SO algorithms and strengthens the foundation of clustering or halo-finding methods in general.

Next-generation ultrahigh-energy (UHE) neutrino telescopes, presently under planning, will have the potential to probe the decay of heavy dark matter (DM) into UHE neutrinos, with energies in excess of ${10}^7\mathrm{GeV}$. Yet, this potential may be deteriorated by the presence of an unknown background of UHE neutrinos, cosmogenic or from astrophysical sources, not of DM origin and seemingly large enough to obscure the DM signature. We show that leveraging the angular and energy distributions of detected events safeguards future searches for DM decay against such backgrounds. We focus on the radio detection of UHE neutrinos in the planned IceCube-Gen2 neutrino telescope, which we model in state-of-the-art detail. We report promising prospects for the discovery potential of DM decay into UHE neutrinos, the measurement of DM mass and lifetime, and limits on the DM lifetime, despite the presence of a large background, without prior knowledge of its size and shape.

The stochastic gravitational-wave background is imprinted on the times of arrival of radio pulses from millisecond pulsars. Traditional pulsar timing analyses fit a timing model to each pulsar and search the residuals of the fit for a stationary time correlation. This method breaks down at gravitational-wave frequencies below the inverse observation time of the array; therefore, existing analyses restrict their searches to frequencies above 1 nHz. An effective method to overcome this challenge is to study the correlation of secular drifts of parameters in the pulsar timing model itself. In this paper, we show that timing model correlations are sensitive to sub-nHz stochastic gravitational waves and perform a search using existing measurements of pulsar spin decelerations and pulsar binary orbital decay rates. We do not observe a signal at our present sensitivity, constraining the stochastic gravitational-wave relic energy density to ${\mathrm{\Omega }}_{\mathrm{GW}}(f)<3.8\times {10}^{-9}$ at 450 pHz with sensitivity that scales as the frequency squared until approximately 10 pHz. We place additional limits on the amplitude of a power-law spectrum of $A_{\star }\lesssim 1.8\times {10}^{-14}$ for a reference frequency of $f_{*}=1{\mathrm{yr}}^{-1}$ and the spectral index expected from supermassive black hole binaries, $\gamma =13/3$. If detection of a supermassive black hole binary signal above 1 nHz is confirmed, this search method will serve as a critical complementary probe of the dynamics of galaxy evolution.

The AMS02 Collaboration has recently published high precision daily measurements of the spectra of cosmic ray protons, helium nuclei and electrons taken during a time interval of approximately 10 years from 2011 to 2020. Positron spectra averaged over distinct 27 day intervals have also been made public. The AMS02 Collaboration has shown some intriguing “hysteresis” effects observed comparing the fluxes of protons and helium nuclei or protons and electrons. In this work we address the question of the origin of these effects. We find that the spectral distortions generated by propagation in the heliosphere are significantly different for particles with electric charge of opposite sign (an effect already well established), with different behavior before and after the solar magnetic field polarity reversal at solar maximum. This results in hysteresis effects for the $p/e^{-}$ comparison that follow the 22-year solar cycle. On the other hand particles with electric charge of the same sign suffer modulations that are approximately equal. The hysteresis effects observed for a helium/proton comparison can then be understood as the consequence of the fact that the two particles have interstellar spectra of different shape, and the approximately equal spectral distortions generated by propagation in the heliosphere have a rigidity dependence that is a function of time. These hysteresis effects can in fact be observed studying the time dependence of the shape of the spectra of a single particle type, and also generate short time looplike structures in the hysteresis curves correlated with large solar activity events such as coronal mass ejections. A description of solar modulations that include these effects must go beyond the simple Force Field Approximation (FFA) model. A minimal, two-parameter generalization of the FFA model that gives a good description of the observations is presented.

The spins of black holes in merging binaries can reveal information related to the formation and evolution of these systems. Combining events to infer the astrophysical distribution of black hole spins allows us to determine the relative contribution from different formation scenarios to the population. Many previous works have modeled spin population distributions using low-dimensional models with statistical or astrophysical motivations. While these are valuable approaches when the observed population is small, they make strong assumptions about the shape of the underlying distribution and are highly susceptible to biases due to mismodeling. The results obtained with such parametric models are valid only if the allowed shape of the distribution is well motivated (i.e., for astrophysical reasons). Unless the allowed shape of the distribution is well motivated (i.e., for astrophysical reasons), results obtained with such models, thus, may exhibit systematic biases with respect to the true underlying astrophysical distribution, along with resulting uncertainties not being reflective of our true uncertainty in the astrophysical distribution. In this work, we relax these prior assumptions and model the spin distributions using a more data-driven approach, modeling these distributions with flexible cubic spline interpolants in order to allow for capturing structures that the parametric models cannot. We find that adding this flexibility to the model substantially increases the uncertainty in the inferred distributions but find a general trend for lower support at high spin magnitude and a spin tilt distribution consistent with isotropic orientations. We infer that 62%–87% of black holes have spin magnitudes less than $a=0.5$ and 27%–50% (90% credible levels) of black holes exhibit negative ${\chi }_{\mathrm{eff}}$. Using the inferred ${\chi }_{\mathrm{eff}}$ distribution, we place a conservative upper limit of 37% for the contribution of hierarchical mergers to the astrophysical binary black hole population. Additionally, we find that artifacts from unconverged Monte Carlo integrals in the likelihood can manifest as spurious peaks and structures in inferred distributions, mandating the use of a sufficient number of samples when using Monte Carlo integration for population inference.

The Telescope Array Collaboration has reported an evidence for existence of a source of ultrahigh-energy cosmic ray events in Perseus-Pisces supercluster. We show that the mere existence of such a source imposes an upper bound on the strength of intergalactic magnetic field (IGMF) in the Taurus void lying between the Perseus-Pisces supercluster and the Milky Way galaxy. This limit is at the level of ${10}^{-10}\mathrm{G}$ for a field with correlation length larger than the distance of the supercluster ($\sim 70\mathrm{Mpc}$). This bound is an order-of-magnitude stronger that the previously known bound on IGMF from radio Faraday rotation measurements and it is the first upper bound on magnetic field in the voids of the large-scale tructure. Our analysis indicates that the source has to be dominated by protons, because heavier nuclei are either photodisintegrated or are too strongly deflected by the Galactic magnetic field.

Dark matter particles in the Galactic Center and halo can annihilate or decay into a pair of neutrinos producing a monochromatic flux of neutrinos. The spectral feature of this signal is unique and it is not expected from any astrophysical production mechanism. Its observation would constitute a dark matter smoking gun signal. We performed the first dedicated search with a neutrino telescope for such signal, by looking at both the angular and energy information of the neutrino events. To this end, a total of five years of IceCube’s DeepCore data has been used to test dark matter masses ranging from 10 GeV to 40 TeV. No significant neutrino excess was found and upper limits on the annihilation cross section, as well as lower limits on the dark matter lifetime, were set. The limits reached are of the order of ${10}^{-24}{\mathrm{cm}}^3/\mathrm{s}$ for an annihilation and up to ${10}^{27}\mathrm{s}$ for decaying dark matter. Using the same data sample we also derive limits for dark matter annihilation or decay into a pair of Standard Model charged particles.

Hadron femtoscopy has turned into a powerful tool for accessing space-time information of heavy-ion collisions as well as for studying final-state interactions of hadrons. Recently, heavy-flavor femtoscopy has become feasible using the ALICE detector at the LHC. We compute the correlation function of $D$ mesons and light mesons using an off-shell $T$-matrix approach to access the two-meson wave function, and predict the correlation functions involving charged $D^{+},D^{*+},D_s^{+}$, and $D_s^{*+}$ with ${\pi }^{\pm }$ and $K^{\pm }$. From the obtained results—all of them accessible in $p+p$ collision experiments—we point up the case of $D^{+}{\pi }^{-}$, which is sensitive to the lower state of the two-pole $D_0^{*}(2300)$ system. The presence of such poles imprints a depletion on the correlation function, which could potentially be detected in experiments. While preliminary ALICE data do not show evidence of this effect, we suggest to look into the $D_s^{+}{K}^{-}$ system to explore the higher pole of the $D_0^{*}(2300)$, as the depletion in the correlation function is more pronounced. Using heavy-quark spin symmetry we also propose exploring the effect of the two poles of the $D_1(2430)$ and predict similar structures in the correlation functions of the $D^{*+}{\pi }^{-}$ and $D_s^{*+}{K}^{-}$ pairs.

In the wake of measurements on $B_c^{+}\to J/\psi K^{+}$, $B_c^{+}\to J/\psi {\pi }^{+}{\pi }^{-}{\pi }^{+}$, and $B_c^{+}\to J/\psi K^{+}{K}^{-}{\pi }^{+}$ at Large Hadron Collider experiments, we propose to study the decays $B_c^{+}\to J/\psi M^{+}$ comprehensively, with $M$ being the light charged pseudoscalar ($P$), vector ($V$), scalar ($S$), axial-vector ($A$), and tensor ($T$) mesons, within the improved perturbative QCD (iPQCD) formalism at leading order in the Standard Model. The theoretical predictions for experimental observables such as branching fractions, relative ratios, and longitudinal polarization fractions in the iPQCD formalism await near future examinations relying on the upgraded Large Hadron Collider, even the forthcoming Circular Electron-Positron Collider. We emphasize that the investigations on the factorizable-emission-suppressed or -forbidden decays like $B_c^{+}\to J/\psi S^{+}$, $B_c^{+}\to J/\psi A_{1{{}^{1}P}_1}^{+}$, and $B_c^{+}\to J/\psi T^{+}$, should go definitely beyond naive factorization to explore the rich dynamics, which could, in turn, further help understand the QCD nature of $B_c$ meson, as well as that of related hadrons. The future confirmations on those predictions about the relative ratios between the branching fractions of $B_c^{+}\to J/\psi b_1(1235{)}^{+}(a_0(980{)}^{+},a_0(1450{)}^{+},a_2(1320{)}^{+})$ and $B_c^{+}\to J/\psi {\pi }^{+}$ could further examine the reliability of this iPQCD formalism. Because of containing only tree-level $\overline{b}\to \overline{c}$ transitions, the $CP$ asymmetries in the $B_c^{+}\to J/\psi M^{+}$ decays exhibit naturally zero.

Dark matter (DM) could be a nonthermal relic that freezes in from extremely weak, sub-Hubble annihilation and decay of Standard Model (SM) particles. The case of Dirac DM freezing in via a dark photon mediator is a well-studied benchmark for DM direct detection experiments. Here, we extend prior work to take into account the possibility that DM is pseudo-Dirac with a small mass splitting. If the mass splitting is greater than twice the electron mass but less than the dark photon mass, there will be distinct cosmological signatures. The excited state ${\chi }_2$ is initially produced in equal abundance to the ground state ${\chi }_1$. Due to the small couplings needed to explain the observed relic abundance, the excited state population can decay at late cosmological times, primarily via the three-body process ${\chi }_2\to {\chi }_1{e}^{+}{e}^{-}$. This injects energetic electrons into the ambient environment, providing observable signatures involving big bang nucleosynthesis, cosmic microwave background spectral distortions and anisotropies, and the Lyman-$\alpha$ forest. Furthermore, the ground state particles that are populated from the three-body decay receive a velocity kick, with implications for DM clustering on small scales. Inelastic freeze-in thus gives a motivated decaying DM candidate, where the long lifetimes are connected to the relic abundance mechanism.

It is possible to formulate theories with many Lee-Wick particles such that a limit exists where the low-energy theory approaches the form of a ghost-free nonlocal theory. Such asymptotically nonlocal quantum field theories have a derived regulator scale that is hierarchically smaller than the lightest Lee-Wick resonance; this has been studied previously in the case of asymptotically nonlocal scalar theories, Abelian and non-Abelian gauge theories, and linearized gravity. Here we consider the dependence on center-of-mass energy of scattering cross sections in these theories. While Lee-Wick resonances can be decoupled from the low-energy theory, scattering amplitudes nonetheless reflect the emergent nonlocality at the scale where the quadratic divergences are regulated. This implies observable consequences in theories designed to address the hierarchy problem, even when the Lee-Wick resonances are not directly accessible.

We demonstrate that novel types of gravitational wave signatures arise in theories with new gauge symmetries broken at high energy scales. For concreteness, we focus on models with gauged baryon number and lepton number, in which neutrino masses are generated via the type I seesaw mechanism, leptogenesis occurs through the decay of a heavy right-handed neutrino, and one of the new baryonic fields is a good dark matter candidate. Depending on the scalar content of the theory, the gravitational wave spectrum consists of contributions from cosmic strings, domain walls, and first order phase transitions. We show that a characteristic double-peaked signal from domain walls or a sharp domain wall peak over a flat cosmic string background may be generated. Those new signatures are within the reach of future experiments, such as Cosmic Explorer, Einstein Telescope, DECIGO, Big Bang Observer, and LISA.

We study the Schwinger model with $N_{\mathrm{f}}\ge 2$ degenerate fermion flavors, by means of lattice simulations. We use dynamical Wilson fermions for $N_{\mathrm{f}}=2$, and reweighted quenched configurations for overlap-hypercube fermions with $N_{\mathrm{f}}\le 6$. In this framework, we explore an analogue of the QCD pion decay constant $F_{\pi }$, which is dimensionless in $d=2$, and which has hardly been considered in the literature. We determine $F_{\pi }$ by three independent methods, with numerical and analytical ingredients. First, we consider the 2-dimensional version of the Gell-Mann–Oakes–Renner relation, where we insert both theoretical and numerical values for the quantities involved. Next we refer to the $\delta$-regime, i.e., a small spatial volume, where we assume formulas from chiral perturbation theory to apply even in the absence of Nambu-Goldstone bosons. We further postulate an effective relation between $N_{\mathrm{f}}$ and the number of relevant, light bosons, which we denote as “pions”. Thus $F_{\pi }$ is obtained from the residual “pion” mass in the chiral limit, which is a finite-size effect. Finally, we address the 2-dimensional Witten–Veneziano formula: it yields a value for $F_{\eta }$, which we identify with $F_{\pi }$, as in large-$N_{\mathrm{c}}$ QCD. All three approaches consistently lead to $F_{\pi }\simeq 1/\sqrt{2\pi }$ at fermion mass $m=0$, which implies that this quantity is meaningful.

We explore the limit at which the effective baryonic Y-string model of the junction approaches the mesonic stringlike behavior. We calculate and compare the numerical values of the static potential and energy-density correlators of diquark-quark and quark-antiquark configurations. The gauge model is pure Yang-Mills $SU(3)$ lattice gauge theory at coupling $\beta =6.0$ and finite temperature. The diquark setup is approximated as two quarks confined within a sphere of radius 0.1 fm. The lattice data of the potential and energy show that the string binding the diquark-quark configuration displays an identical behavior to the quark-antiquark confining string. However, with the temperature increase to a small enough neighborhood of the critical point $T_c$, the gluonic similarities between the two systems do not manifest neither at short nor intermediate distance scales $R<1.0\mathrm{fm}$. The comparison between the potential and the second moment of the action-density correlators for both systems shows significant splitting. This suggests that subsisted baryonic decoupled states overlap with the mesonic spectrum. The baryonic junction’s model for the potential and the profile returns a good fit to the numerical lattice data of the diquark-quark arrangement. However, near the critical point, the mesonic string displays large deviations compared to fits of the corresponding quark-antiquark data.

It remains unclear in general how the pole skipping appears as a physical phenomenon, and we study the issue in the context of the anti–de Sitter soliton. The pole skipping has been discussed in black hole backgrounds, but the pole skipping occurs even in the anti–de Sitter soliton background. The geometry has a compact $S^1$ direction, and we compute the mass spectrum for the bulk scalar field, the bulk Maxwell field, and the gravitational perturbations with $S^1$ momentum. We show that the pole skipping leaves its fingerprint in the normal mode spectrum. The spectrum has some puzzling features because the wouldbe states are missing at pole-skipping points. The puzzling features disappear once one takes into account these pole-skipping points that we call “missing states.”

We propose a doubly holographic version of the semiclassical island formula for the entanglement negativity in the framework of the defect AdS/BCFT correspondence where the anti–de Sitter (AdS) bulk contains a defect conformal matter theory. In this context, we propose a defect extremal surface (DES) formula for computing the entanglement negativity modified by the contribution from the defect matter theory on the end-of-the-world brane. The equivalence of the DES proposal and the semiclassical island formula for the entanglement negativity is demonstrated in ${\mathrm{AdS}}_3/{\mathrm{BCFT}}_2$ framework. Furthermore, in the time-dependent ${\mathrm{AdS}}_3/{\mathrm{BCFT}}_2$ scenarios involving eternal black holes in the lower dimensional effective description, we investigate the time evolution of the entanglement negativity through the DES and the island formulas and obtain the analogs of the Page curves.

In this work we analyze the existence of electrically charged scalar clouds which are bound states of a complex-valued massive scalar field in the background of subextremal and extremal Kerr-Newman black holes (BH). In particular, we reanalyze neutral (uncharged) clouds in extremal Kerr BHs. For the extremal scenarios we have implemented a novel technique which allows us to obtain regular clouds at the BH horizon ${\mathcal{H}}^{+}$ which turn out to be connected “continuously” with the cloud solutions in the subextremal case even if some derivatives of the scalar field are unbounded at the horizon. In particular, for subextremal BHs we have established regularity conditions at ${\mathcal{H}}^{+}$, by demanding that the field and its radial derivatives are bounded there, but in the extremal scenarios we relax this last condition while demanding that some scalar invariants are well-behaved at ${\mathcal{H}}^{+}$. Furthermore we have implemented an integral technique to understand and justify in a simple and heuristic way the existence of such cloud configurations in those BH backgrounds.