We propose a new mechanism of absorption of dark matter particles in atoms which resembles the Migdal effect of inelastic dark matter scattering. In this process, atoms may be ionized upon absorption of a scalar particle through the scalar-nucleon Yukawa-type interaction. The crucial difference from the inelastic dark matter scattering on atoms is that the total energy of the particle, including its rest mass $m{c}^2$ term, is transferred to the electron. As a result, the emitted electron kinetic energy is about 6 orders in magnitude bigger than that in the dark matter scattering process. This absorption process allows one to probe dark matter particles with a relatively small mass, in the range from 1 to 100 keV, that cannot be detected in the scattering process. It is also possible to detect hypothetical scalar particles emitted from the Sun. We calculate absorption cross sections of this process in Na, Si, Ar, Ge, I, Xe, and Tl target atoms and extract limits on the scalar-nucleon interaction constant from null results of the XENONnT experiment.

We discuss a simple theory for neutrino masses where the total lepton number is a local gauge symmetry spontaneously broken below the multi-TeV scale. In this context, the neutrino masses are generated through the canonical seesaw mechanism and a Majorana dark matter candidate is predicted from anomaly cancellation. We discuss in great detail the dark matter annihilation channels and find out the upper bound on the symmetry-breaking scale using the cosmological bounds on the relic density. Since in this context the dark matter candidate has suppressed couplings to the Standard Model quarks, one can satisfy the direct detection bounds even if the dark matter mass is close to the electroweak scale. This theory predicts a light pseudo-Nambu-Goldstone boson (the Majoron) associated to the mechanism of neutrino mass. We discuss briefly the properties of the Majoron and the impact of the big bang nucleosynthesis bounds.

In this work, we investigate the momentum-dependent drag and diffusion coefficient of heavy quarks ($\mathrm{HQs}$) moving in the quark-gluon plasma background. The leading order scattering amplitudes required for this purpose have been obtained using the Gribov-Zwanziger propagator for the mediator gluons to incorporate the nonperturbative effects relevant to the phenomenologically accessible temperature regime. The drag and diffusion coefficients so obtained have been implemented to estimate the temperature and momentum dependence of the energy loss of the HQ as well as the temperature dependence of the specific shear viscosity ($\eta /s$) of the background medium. Our results suggest a higher energy loss of the propagating HQ compared to the perturbative estimates, whereas the $\eta /s$ is observed to comply with the AdS/CFT estimation over a significantly wider temperature range compared to the perturbative expectation.

In this paper, we demonstrate how black hole quasinormal modes can emerge from a Dirichlet brickwall model normal modes. We consider a probe scalar field in a Baños-Teitelboim-Zanelli geometry with a Dirichlet brickwall and demonstrate that as the wall approaches the event horizon, the corresponding poles in the retarded correlator become dense and yield an effective branch cut. The associated discontinuity of the correlator carries the information of the black hole quasinormal modes. We further demonstrate that a nonvanishing angular momentum nonperturbatively enhances the pole condensing. We hypothesize that it is also related to quantum chaotic features of the corresponding spectral form factor, which has been observed earlier. Finally, we discuss the underlying algebraic justification of this approximate thermalization in terms of the trace of the algebra.

We study general correlation functions of various quantum field theories in the holographic setup. Following the holographic proposal, we investigate correlation functions via a geodesic length connecting boundary operators. We show that this holographic description can reproduce the known two- and three-point functions of conformal field theory. Using this holographic method, we further study general two-point functions of a two-dimensional thermal conformal field theory (CFT) and of a scalar field theory living in a de Sitter or anti–de Sitter space. Due to the nontrivial thermal or curvature effect, the two-point functions in an IR limit show different scaling behaviors from those of the UV CFT. We study such nontrivial IR scaling behaviors by applying the holographic method.

We investigate the transition amplitudes of the Unruh-DeWitt detector within the Schwarzschild spacetime background and discover gravity-induced transparency phenomena akin to the earlier acceleration-induced transparency. This is confirmed through calculations performed in both the Hartle-Hawking and Unruh states. The similarity between free-falling detectors in these states and accelerated detectors in electromagnetic fields is noteworthy, as it parallels the scenario in which acceleration-induced transparency phenomena occur.

Ultracompact objects (UCOs) are horizonless compact objects that present light rings (LRs): circular photon orbits. As a result, they could be black hole mimickers. Some years ago, Cunha et al. established a theorem stating that, under general assumptions, UCOs formed from smooth, quasi-Minkowski initial data, must have at least a pair of LRs, one of which must be stable. These stable LRs are supposed to trigger a nonlinear instability in spacetime, potentially weakening UCOs’ ability to replicate black hole phenomenology. However, this LR theorem does not extend to wormholes, which represent topologically nontrivial spacetimes. We address the wormhole case by proving the following theorem: a stationary, axisymmetric, asymptotically flat, traversable wormhole in $1+3$ dimensions, connecting two different asymptotic regions, has at least one standard LR for each rotation sense. Thus, any (such) wormhole is an UCO. By filling this gap, our results not only broaden the horizon of knowledge on UCOs but also highlight their potential to closely mimic black hole phenomenology.

In this paper, we apply a novel approach based on physics-informed neural networks to the computation of quasinormal modes of black hole solutions in modified gravity. In particular, we focus on the case of Einstein-scalar-Gauss-Bonnet theory, with several choices of the coupling function between the scalar field and the Gauss-Bonnet invariant. This type of calculation introduces a number of challenges with respect to the case of general relativity, mainly due to the extra complexity of the perturbation equations and to the fact that the background solution is known only numerically. The solution of these perturbation equations typically requires sophisticated numerical techniques that are not easy to develop in computational codes. We show that physics-informed neural networks have an accuracy which is comparable to traditional numerical methods in the case of numerical backgrounds, while being very simple to implement. Additionally, the use of GPU parallelization is straightforward thanks to the use of standard machine learning environments.

The detection of a subsolar object in a compact binary merger is regarded as one of the smoking gun signatures of a population of primordial black holes (PBHs). We critically assess whether these systems could be distinguished from stellar binaries, for example composed of white dwarfs or neutron stars, which could also populate the subsolar mass range. At variance with PBHs, the gravitational-wave signal from stellar binaries is affected by tidal effects, which dramatically grow for moderately compact stars as those expected in the subsolar range. We forecast the capability of constraining tidal effects of putative subsolar neutron star binaries with current and future LIGO-Virgo-KAGRA (LVK) sensitivities as well as next-generation experiments. We show that, should LVK O4 run observe subsolar neutron-star mergers, it could measure the (large) tidal effects with high significance. In particular, for subsolar neutron-star binaries, O4 and O5 projected sensitivities would allow measuring the effect of tidal disruption on the waveform in a large portion of the parameter space, also constraining the tidal deformability at $\mathcal{O}(10\%)$ level, thus excluding a primordial origin of the binary. Vice versa, for subsolar PBH binaries, model-agnostic upper bounds on the tidal deformability can rule out neutron stars or more exotic competitors. Assuming events similar to the subthreshold candidate SSM200308 reported in LVK O3b data are PBH binaries, O4 projected sensitivity would allow ruling out the presence of neutron-star tidal effects at $\approx 3\sigma$ CL, thus strengthening the PBH hypothesis. Future experiments would lead to even stronger ($>5\sigma$) conclusions on potential discoveries of this kind.

In this study, we develop a numerical method to generate images on an observer’s screen, formed by radiation from hot spots on any timelike orbits outside a black hole. This method uses the calculation of fractional numbers, enabling us not only to produce the overall image but also to distinguish between primary, secondary, and higher-order images. Building upon this, we compute the images of hot spots from eight potential types of geodesic timelike orbits outside a Kerr black hole, summarizing the properties of both the overall and individual order images. Furthermore, we calculate the centroid motion and light curve. Notably, we observe flare phenomena across all orbit types and classify these flares into three categories based on the Doppler and gravitational redshift effects.

Galaxy angular momenta (spins) contain valuable cosmological information, complementing their positions and velocities. The baryonic spin direction of galaxies has been probed as a reliable tracer of their host halos and the primordial spin modes. Here we use the TNG100 simulation of the IllustrisTNG project to study the spin magnitude correlations between dark matter, gas, and stellar components of galaxy-halo systems and their evolutions across cosmic history. We find that these components generate similar initial spin magnitudes from the same tidal torque in Lagrangian space. At low redshifts, the gas component still traces the spin magnitude of the dark matter halo and the primordial spin magnitude. However, the traceability of the stellar component depends on the ex situ stellar mass fraction, $f_{\mathrm{acc}}$. Our results suggest that the galaxy baryonic spin magnitude can also serve as a tracer of their host halo and the initial perturbations, and the galaxy-halo correlations are affected by the similarity of their evolution histories.

We present a machine learning approach using normalizing flows for inferring cosmological parameters from gravitational wave events. Our methodology is general to any type of compact binary coalescence event and cosmological model and relies on the generation of training data representing distributions of gravitational wave event parameters. These parameters are conditional on the underlying cosmology and incorporate prior information from galaxy catalogues. We provide an example analysis inferring the Hubble constant using binary black holes detected during the O1, O2, and O3 observational runs conducted by the advanced LIGO/VIRGO gravitational wave detectors. We obtain a Bayesian posterior on the Hubble constant from which we derive an estimate and $1\sigma$ confidence bounds of $H_0=74.51_{-13.63}^{+14.80}\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$. We are able to compute this result in $\mathcal{O}(1)\mathrm{s}$ using our trained normalizing flow model.

The gravitational wave signals detected by the LIGO-Virgo-KAGRA collaboration can be explained by mergers of binary primordial black holes (PBHs) formed in the radiation dominated epoch. However, in early structures induced by the Poisson distribution of PBHs, a significant fraction of binaries are perturbed and avoid mergers. In addition, the internal dynamics of early halos lead to the formation of dense primordial black hole clusters within a few Hubble times from the moment of halo formation. In such clusters PBH binaries are effectively formed and their mergers potentially dominate in the modern era. We obtained that the PBH merger rate changes with redshift as $\mathcal{R}\propto (1+z{)}^{\beta }$, where $\beta =1.4–2.2$ reflects the influence of PBH clustering and depends on both $z$ and $f_{\mathrm{PBH}}$. The observed merger rate constraints the fraction of PBHs of tens solar masses in the composition of dark matter $f_{\mathrm{PBH}}\lesssim 0.001–0.1$ in dependence of the clustering efficiency.

I review and discuss the possible implications for inflation resulting from considering new physics in light of the Hubble tension. My study is motivated by a simple argument that the constraints on inflationary parameters, most typically the spectral index $n_s$, depend to some extent on the cosmological framework. To avoid broadening the uncertainties resulting from marginalizing over additional parameters (typical in many alternative models), I first adopt the same alternative viewpoint of previous studies and analyze what happens if a physical theory can fix extra parameters to nonstandard values. Focusing on the dark energy equation of state $w$ and the effective number of relativistic species $N_{\mathrm{eff}}$, I confirm that physical theories able to fix $w\approx -1.2$ or $N_{\mathrm{eff}}\approx 3.9$ produce values of $H_0$ from Cosmic Microwave Background and Baryon Acoustic Oscillations in line with the local distance ladder estimate. While in the former case I do not find any relevant implications for inflation, in the latter scenarios, I observe a shift toward $n_s\approx 1$. From a model-selection perspective, both cases are strongly disfavored compared to $\mathrm{\Lambda }$ cold dark matter. However, models with $N_{\mathrm{eff}}\approx 3.3–3.4$ could bring the $H_0$ tension down to $\sim 3\sigma$ while being moderately disfavored. Yet, this is enough to change the constraints on inflation so that the most accredited models (e.g., Starobinsky inflation) would no longer be favored by data. I then focus on Early Dark Energy (EDE), arguing that an EDE fraction $f_{\mathrm{EDE}}\sim 0.04–0.06$ (only able to mildly reduce the $H_0$ tension down to $\sim 3\sigma$) could already require a similar change in perspective on inflation. In fact, performing a full joint analysis of EDE and Starobinsky inflation, I find that the two models can hardly coexist for $f_{\mathrm{EDE}}\gtrsim 0.06$.

The nature of the GeV gamma-ray Galactic Center excess (GCE) in the data of Fermi-Large Area Telescope (LAT) is still to be unveiled. We present a new analysis of the inner Galaxy Fermi-LAT data at energies above 10 GeV, based on an innovative method which combines the skyFACT adaptive template fitting with and the 1pPDF pixel-count statistics. We find a strong evidence for the GCE also at high energies, $\sigma >5$ regardless of the GCE spatial template. Remarkably, our fits prefer the bulge morphological model over the dark matter one at high significance, and show no evidence for an additional dark matter template on top of the bulge component. Through the 1pPDF analysis, we find that the model best describing the gamma-ray data requires a smooth, diffuse GCE following a bulge morphology, together with sub-threshold point sources. The 1pPDF fit reconstructs a consistent population of faint point sources down at least to ${10}^{-12}\mathrm{ph}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. Between ${10}^{-12}\mathrm{ph}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ and ${10}^{-11}\mathrm{ph}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ the 1pPDF measures a number of point sources significantly higher than the ones in the Fermi 4FGL catalog. The robustness of our results brings further support to the attempt of explaining, at least partially, the high-energy tail of the GCE in terms of a population of point sources, likely corresponding to millisecond pulsars.

High-resolution infrared data have revealed several young stars in close proximity to Sgr A*. These stars may encounter extremely high dark matter densities. We examine scenarios where dark matter scatters on stellar gas, accumulates in stellar cores, and then annihilates. We study the stars S2, S62, S4711, and S4714 and find three observable effects. First, dark matter interactions can inhibit in situ star formation close to Sgr A*, favoring scenarios where these stars migrate into the Galactic Center. Second, dark matter interactions can delay main sequence evolution, making stars older than they appear. Third, very high dark matter densities can inject enough energy to disrupt main sequence stars, allowing S-star observations to constrain the dark matter density near Sgr A*.

We have phenomenologically investigated the decays $B_s^0\to X(3872){\pi }^{+}{\pi }^{-}(K^{+}{K}^{-})$ and $B_s^0\to \psi (2S){\pi }^{+}{\pi }^{-}(K^{+}{K}^{-})$. In our analysis, the scalar meson $f_0(980)$ is formed through the final state interactions of coupled channels $\pi \pi$ and $K\overline{K}$. Our findings indicate that the ${\pi }^{+}{\pi }^{-}$ invariant mass distribution of the $B_s^0\to \psi (2S){\pi }^{+}{\pi }^{-}$ decay can be accurately reproduced. Furthermore, we have explored the ${\pi }^{+}{\pi }^{-}(K^{+}{K}^{-})$ invariant mass distribution of the $B_s^0\to X(3872){\pi }^{+}{\pi }^{-}(K^{+}{K}^{-})$ decay, accounting for the different production mechanisms between $X(3872)$ and $\psi (2S)$, up to a global factor. It is found that the production rates for $X(3872)$ and $\psi (2S)$ are much different, which indicates that the structure of $X(3872)$ is more complicated than the $\psi (2S)$, which is a conventional $c\overline{c}$ state. Additionally, we have considered the contributions from $f_0(1500)$ to ${\pi }^{+}{\pi }^{-}$ and the $\varphi$ meson to $K^{+}{K}^{-}$ in our analysis. Utilizing the model parameters, we have calculated the branching fraction of $B_s^0\to X(3872)K^{+}{K}^{-}$, and anticipate that the findings of our study can be experimentally tested in the future.

We propose generalized no-scale supergravity, the simplest scenario for effective supernatural supersymmetry, naturally solving the supersymmetry electroweak fine-tuning problem and including natural dark matter. A light right-handed slepton bulk region is realized in $\mathcal{F}$-SU(5) and the phenomenological minimal supersymmetric standard model. The bulk may be beyond the LHC reach, although it can be probed at the 1000-day LUX-ZEPLIN, Future Circular Collider at CERN, Circular Electron-Positron Collider, and Hyper-Kamiokande.