We investigate fluctuations of hot and dense QCD plasma by using the gauge/gravity duality. To this end, we carry out a comprehensive classification and analysis of quasinormal modes of charged black holes in the holographic V-QCD model. It turns out that the Chern-Simons term determined by the flavor anomalies of QCD is strong enough to drive a modulated instability. While such an instability is expected at high densities, we find that the unstable phase extends to surprisingly low densities and high temperatures, close to the region where data from lattice simulations are available. We also analyze the limit of small temperature which is controlled by a quantum critical ${\mathrm{AdS}}_2$ point. We study in detail the signatures of the critical point in the quasinormal mode spectrum, focusing on the interplay between the hydrodynamic modes and other modes.

We discuss the scattering process of a scalar field having a time-dependent mass with another scalar field having a constant mass as a toy model of the scattering problems during preheating after inflation. Despite a general difficulty of analytically solving such models, in our previous work [QFT approach to dressed particle processes in preheating and non-perturbative mechanism in kinematically-forbidden regime, J. High Energy Phys. 02 (2023) 048], we considered an exactly calculable model of such scattering processes with a time-dependent mass of the form $m^2(t)\supset {\mu }^4{t}^2$ and the time-dependence never disappears formally. In this work, we discuss another exactly calculable model with a time-dependent mass that has a spike/peak but asymptotes to a constant, which effectively appears in the preheating model of Higgs inflation with a nonminimal coupling. Thanks to the localized time-dependence of the mass, the daughter particle number density behaves in a physically reasonable way contrary to the one in our previous model due to the infinite time-dependent mass in the asymptotic future. On the other hand, we find that the daughter particle experiences the kinematically forbidden process, which is a nonperturbative phenomenon found in our previous work. As in the previous model, the kinematically forbidden process produces daughter particles exponentially more than the parent particle having the time-dependent mass, which never happens for particle decay processes without time-dependent backgrounds. This result supports the existence of such a nonperturbative particle production process in general time-dependent backgrounds.

We classify all possible cosmological homogeneous and isotropic Landsberg-type Finsler structures, in four dimensions. Among them, we identify viable nonstationary Finsler spacetimes, i.e., those geometries leading to a physical causal structure and a dynamical universe. Noting that any nonstationary and non-Riemannian Landsberg metric must be actually also non-Berwald (i.e., it should be a so-called “unicorn”), we construct the unique Finsler, non-Berwaldian Landsberg generalization of Friedmann-Lemaître-Robertson-Walker geometry.

We study stationary clouds of a gauged, complex scalar field on a magnetically (and possibly electrically as well) charged Kerr-Newman black hole (BH). The existence of a magnetic charge $Q_m$ promotes a north-south asymmetry of the scalar clouds. This breakdown of the clouds’ ${\mathbb{Z}}_2$-symmetry carries through to the spacetime geometry for the nonlinear continuation of the clouds: a family of magnetically charged (or dyonic) BHs with synchronized gauged scalar hair, which we construct. Their distinct phenomenology is illustrated by their imaging, exhibiting skewed shadows and lensing. Such hairy BHs could, in principle, result from the superradiant instability of magnetically charged Kerr-Newman BHs, unveiling a dynamical mechanism for creating north-south asymmetric BHs from standard ${\mathbb{Z}}_2$-symmetric electrovacuum BHs.

The general motion of spinning test particles to the leading-order approximation of spin in the braneworld spacetime is investigated. Analytical integrations for the equations of motion and linear shifts in orbital frequency are obtained. As a result, we found that both the nodal precession and the periastron one become larger when the tidal charge $b$ of the braneworld spacetime becomes smaller. For the periastron precession, the effect is further amplified as the spin increases. Energy and angular momentum fluxes under the quadrupole approximation and the orbit in extreme mass ratio inspirals are also calculated, hence providing a viable framework to the study of gravitational waveforms with spin in the braneworld spacetime.

With the aim of testing massive gravity in the context of black hole physics, we investigate the gravitational radiation emitted by a massive particle plunging into a Schwarzschild black hole from slightly below the innermost stable circular orbit. To do so, we first construct the quasinormal and quasibound resonance spectra of the spin-2 massive field for odd and even parity. Then, we compute the waveforms produced by the plunging particle and study their spectral content. This allows us to highlight and interpret important phenomena in the plunge regime, including (i) the excitation of quasibound states, with particular emphasis on the amplification and slow decay of the post-ringdown phase of the even-parity dipolar mode due to harmonic resonance; (ii) during the adiabatic phase, the waveform emitted by the plunging particle is very well described by the waveform emitted by the particle living on the innermost stable circular orbit, and (iii) the regularized waveforms and their unregularized counterparts constructed from the quasinormal mode spectrum are in excellent agreement. Finally, we construct, for arbitrary directions of observation and, in particular, outside the orbital plane of the plunging particle, the regularized multipolar waveforms, i.e., the waveforms constructed by summing over partial waveforms.

We study the wave form emitted by a particle moving along an arbitrary (in general open) geodesic of the Schwarzschild geometry. The mathematical problem can be phrased in terms of quantities in $\mathcal{N}=2$ supersymmetric gauge theories that can be calculated by using localization and the Alday-Gaiotto-Tachikawa correspondence. In particular through this mapping, the post-Newtonian expansion of the wave form is expressed as a double instanton sum with rational coefficients that resums all tail contributions into Gamma functions and exponentials. The formulas we obtain are valid for generic values of the orbital quantum numbers $\ell$ and $m$. For $\ell =2$, 3 we check explicitly that our results agree with the small mass ratio limit of the wave forms derived in the multipole post-Minkowskian and the amplitudes approaches. We show how the so-called tails and tails-of-tails contributions to the wave form arise in our approach. Finally, we derive a universal formula for the soft limit of the wave form that resums all logarithmic terms of the form ${\omega }^{n-1}(\log \omega {)}^n$.

Superradiance, the process by which waves are amplified through energy and angular momentum transfer, can also occur in horizonless objects like boson stars, due to both the real space and internal field space rotations. In this work, we study superradiance in the frequency and time domains for static and spinning boson stars, constructed within general relativity and with a self-interacting complex scalar field as a matter source. Using linear perturbation theory and three dimensional nonlinear simulations, we calculate amplification factors and analyze energy and angular momentum transfer in scattering processes, with results showing consistency between approaches. Wave scattering inside a cavity containing a boson star is also examined, demonstrating the effects of confinement on amplification.

We study strong gravitational lensing by a specific one-parameter extension of Kerr spacetime, a Kerr-like wormhole, characterized by a single parameter specifying the throat’s location. We classify the roots of the radial potential derived from the null geodesic equations. We focus on the conditions required for the throat, together with the other roots, to become either a double root or a triple root, potentially leading to the divergence of the deflection angle of the light rays in the strong deflection limit (SDL). In particular, while a logarithmic divergence of the deflection angle is known to occur as the closest distance $r_0$ of an incident light trajectory around a black hole approaches a double root, a stronger power-law (nonlogarithmic) divergence is found as $r_0$ approaches a triple root especially in a wormhole. In addition, the effective potential in terms of the proper distance from the throat is constructed, with which one can see how the light rays can either travel within a single spacetime, where both the source and the observers are located, or pass from the source through the throat into another spacetime where different observers reside. Observational effects, such as relativistic images resulting from the deflection of light by wormholes, are discussed, and they could serve as a unique feature of wormholes.

The reheating temperature plays a crucial role in the early Universe’s evolution, marking the transition from inflation to the radiation-dominated era. It directly impacts the number of $e$-folds and, consequently, the observable parameters of inflation, such as the spectral index of scalar perturbations. By establishing a relationship between the gravitational reheating temperature and the spectral index, we can derive constraints on inflationary models. Specifically, the range of viable reheating temperatures imposes bounds on the spectral index, which can then be compared with observational data, such as those from the Planck satellite, to test the consistency of various models with cosmological observations. Additionally, in the context of dark matter production, we demonstrate that gravitational reheating provides a viable mechanism when there is a relationship between the mass of the dark matter particles and the mass of the particles responsible for reheating. This connection offers a pathway to link dark matter genesis with inflationary and reheating parameters, allowing for a unified perspective on early Universe dynamics.

Cold new early dark energy (cold NEDE) addresses the Hubble tension through a triggered vacuum phase transition in the dark sector. In this paper, we constrain a phenomenological fluid model using recent cosmic microwave background likelihoods based on Planck NPIPE data alongside baryonic acoustic oscillations (BAO) and supernovae data from Pantheon+. Exploiting the enhanced constraining power of the datasets, we introduce and study an extended version of the NEDE fluid model in which the equation of state parameter $w_{\mathrm{NEDE}}$, characterizing the fluid after the phase transition, is allowed to evolve with nonvanishing derivatives $d{w}_{\mathrm{NEDE}}/d\ln a$ and $d^2{w}_{\mathrm{NEDE}}/d(\ln a{)}^2$. Our results indicate that data is compatible with a rather simple time dependence that could arise from a mixture of radiation and a stiff fluid. With the updated datasets, the base and extended models still show a significant reduction of the difference of the maximum a posteriori tension from $6.3\sigma$ in $\mathrm{\Lambda }\mathrm{CDM}$ down to $3.5\sigma$ with a small simultaneous reduction of the $S_8$ tension, slightly improving over recent findings for the axionlike early dark energy model. Finally, we also provide a first test of the model against new BAO data from the dark energy spectroscopic instrument survey. Replacing the previous BAO constraints in our analysis with the new ones, the tension is further reduced to $2.6\sigma$, reaffirming the cold NEDE model as a promising solution to the Hubble tension.

We derive new constraints on the $E_G$ statistic as a test of gravity, combining the cosmic microwave background (CMB) lensing map estimated from Data Release 6 (DR6) of the Atacama Cosmology Telescope with Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (SDSS BOSS) CMASS and LOWZ galaxy data. We develop an analysis pipeline to measure the cross-correlation between CMB lensing maps and galaxy data, following a blinding policy and testing the approach through null and consistency checks. By testing the equivalence of the spatial and temporal gravitational potentials, the $E_G$ statistic can distinguish $\mathrm{\Lambda }\mathrm{CDM}$ from alternative models of gravity. We find $E_G(z_{\mathrm{eff}}=0.555)=0.31_{-0.05}^{+0.06}$ for Atacama Cosmology Telescope (ACT) and CMASS data at 68.28% confidence level, and $E_G(z_{\mathrm{eff}}=0.316)=0.49_{-0.11}^{+0.14}$ for the ACT and LOWZ. Systematic errors are estimated to be 3% and 4%, respectively. Including CMB lensing information from Planck PR4 results in $E_G(z_{\mathrm{eff}}=0.555)=0.34_{-0.05}^{+0.05}$ with CMASS and $E_G(z_{\mathrm{eff}}=0.316)=0.43_{-0.09}^{+0.11}$ with LOWZ. These are consistent with predictions for the $\mathrm{\Lambda }\mathrm{CDM}$ model that best fits the Planck CMB anisotropy and SDSS BOSS baryon acoustic oscillations (BAO), where $E_G^{\mathrm{GR}}(z_{\mathrm{eff}}=0.555)=0.401\pm 0.005$ for CMB lensing combined with CMASS and $E_G^{\mathrm{GR}}(z_{\mathrm{eff}}=0.316)=0.452\pm 0.005$ combined with LOWZ. We also find $E_G$ to be scale independent, with probability to exceed $>5\%$, as predicted by general relativity. The methods developed in this work are also applicable to improved future analyses with upcoming spectroscopic galaxy samples and CMB lensing measurements.

Axionic dark matter can form miniclusters and minicluster halos (MCHs) from inhomogeneities in the early Universe. If MCHs are sufficiently massive, then their existence can be revealed by small-scale gravitational tidal perturbation to halolike wide binary star systems in the Galaxy. The observed population of the Milky Way’s wide-separation binaries with $a\gtrsim 0.1$ parsec offer a sensitive test to dynamic evaporation from MCHs. Considering data from recent GAIA observations, we derive significant constraints on the MCH fraction of the Galactic dark matter halo. For several scenarios including dense MCHs and isolated minicluster models, these limits will apply to axionlike particles in the mass range $m_a\sim {10}^{-15}–{10}^{-12}\mathrm{eV}$ and $m_a\sim {10}^{-19}–{10}^{-16}\mathrm{eV}$, respectively.

Tidal disruption event iPTF16fnl shows a relatively low optical flare with observationally very weak x-ray emission and the spectroscopic property that the helium emission line from the source dominates over the hydrogen emission line at early times. We explore these observed signatures by calculating spectral emission lines with the publicly available code cloudy. We estimate five physical parameters by fitting the observed optical UV spectra on multiple days to a theoretical model of a steady-state, slim disk with a spherical outflow. The resultant key parameters among them are black hole mass $M_{•}\sim 4.43\times {10}^5{M}_{\odot }$, stellar mass $M_{\star }\sim 0.46M_{\odot }$, and wind velocity $v_{\mathrm{w}}\sim 5382.7\mathrm{km}{\mathrm{s}}^{-1}$. The disk-wind model also estimates the radiative efficiency to be $0.01\lesssim \eta \lesssim 0.04$ over the observational time, resulting in the disk being radiatively inefficient. In our cloudy model, the filling factor of the wind is also estimated to be 0.8, suggesting that the wind is moderately clumpy. We reveal that the helium-to-hydrogen number density ratio of the wind lies between 0.1 and 0.15, which is nearly the same as the solar case, suggesting the tidally disrupted star is originally a main sequence star. Because the optical depth of the helium line is lower than the hydrogen line by 2 orders of magnitude, the helium line is significantly optically thinner than the hydrogen line. Consequently, our results indicate that the helium line luminosity dominates the hydrogen line luminosity due to the optical depth effect despite a small helium-to-hydrogen number density ratio value.

We investigate the influence of inelastic neutrino microphysics in general-relativistic magnetohydrodynamics simulations of a hypermassive neutron star. In particular, we include species/energy groups coupled neutrino-matter interactions, such as inelastic neutrino-electron scattering and electron-positron annihilation kernels, into simulations up to 50 ms. Neutrino-electron inelastic scattering is known to have effective neutrino-matter energy exchange. We show that, with neutrino-electron inelastic scattering, simulations predict 75% higher disc mass with slightly different mass-averaged compositions, and 18% more ejected mass with similar distributions. The enhancement of the mass of the disc and the ejecta results in stronger baryon pollution, leading to less favorable jet launching environments. Furthermore, neutrino luminosities are about 50%, 40%, and 30% higher for electron neutrino, electron antineutrino, and heavy-lepton neutrinos. In contrast, we do not see any significant impacts due to electron-positron annihilation.

We study the next-to-leading order (NLO) electroweak (EW) corrections to the $\gamma \gamma \to {\tau }^{+}{\tau }^{-}$ process in a Pb-Pb ultraperipheral collision (UPC). We find that the EW correction $\delta {\sigma }_{\mathrm{EW}}$ decreases the total cross section ${\sigma }_{\mathrm{NLO}}={\sigma }_{\mathrm{LO}}+\delta {\sigma }_{\mathrm{EW}}$ by $-3\%$ at Pb-Pb center-of-mass energy $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. The weak correction plays a significant role whose contribution is about–4 times that of QED. The CMS and ATLAS Collaborations use the reaction $\gamma \gamma \to {\tau }^{+}{\tau }^{-}$ in Pb-Pb and proton-proton UPCs to constrain tau’s anomalous magnetic moment $a_{\tau }$. By parametrizing the $\gamma \tau \tau$ vertex with two form factors $F_{1,2}$, the cross section can be written as ${\sigma }_{a_{\tau }}={\sigma }_{\mathrm{LO}}+\delta {\sigma }_{a_{\tau }}$, where $\delta {\sigma }_{a_{\tau }}$ is proportional to $a_{\tau }$. The impact of NLO EW corrections on $a_{\tau }$ bounds in a Pb-Pb UPC is limited, as the current experimental bounds are loose. We also find that various differential distributions of the two ratios $\mathrm{d}{\sigma }_{\mathrm{NLO}}/\mathrm{d}{\sigma }_{\mathrm{LO}}$ and $\mathrm{d}{\sigma }_{a_{\tau }}/\mathrm{d}{\sigma }_{\mathrm{LO}}$ have different line shapes. This work is significant to precisely study the interaction of $\gamma \tau \tau$ via the $\gamma \gamma \to {\tau }^{+}{\tau }^{-}$ process.

Many motivated extensions of the standard model include new light bosons, such as axions and dark photons, which can mix with the ordinary photon. This latter, when in a dilute plasma, can be dressed by an effective plasma mass. If this is equal to the mass of the new degree of freedom, then a resonance takes place and the probability of transition between states is enhanced. This phenomenon of resonant conversion is at the very basis of multiple probes of dark matter, and it is typically studied within the so-called Landau-Zener approximation for level crossings. This latter is known to break down in a variety of scenarios, such as multiple level crossings or when the de Broglie wavelength of the new boson is comparable to the scale over which the background plasma varies. We develop a flexible code adopting a $3+1$ formalism in flat spacetime to perform nonlinear simulations of systems with photons and new ultralight bosons in the presence of plasma. Our code currently allows to evolve one-dimensional systems, which are the ones of interest for this first study, but can be extended to treat three-dimensional spaces, and can be adapted to describe a plethora of realistic astrophysical and cosmological situations. Here we use it to study the breakdown of the Landau-Zener approximation in the case of multiple level crossings and when the slowly varying plasma approximation ceases to be valid. In this first paper we detail our code and use it to study nonturbulent plasma, where small-scale fluctuations can be neglected; their treatment will be considered in an upcoming publication.

We compute the baryon asymmetry in decay and scattering processes involving the electromagnetically charge-neutral fermion $\chi$ that carries the nonzero baryon number and interacts with quarklike fermions $U$, $D$ via a vector-vector dimension-six effective operator, in the theory we developed in our earlier work. Majorana masses for the $\chi$ break the baryon number and split the Dirac fermion $\chi$ into a pair of Majorana fermions ${\mathcal{X}}_n$ with an indefinite baryon number. We identify loop amplitudes for ${\mathcal{X}}_n$ decay and scattering processes that are sensitive to the baryon number violation. The phases in the Majorana mass and couplings, in conjunction with the phase from intermediate on-shell states, lead to $C$ and $CP$ violation in these processes. For some representative parameter choices, we numerically compute the decay and scattering baryon asymmetries between the process and its conjugate process and find that the asymmetry generated is very interesting for explaining the baryon asymmetry of the Universe.

We propose the ${\mu }^{-}\to e^{-}\gamma$ process in a muonic atom as a novel means to investigate charged lepton flavor violation (CLFV). We demonstrate its sensitivity in probing effective CLFV operators associated with both single and double photon fields. In comparison to ${\mu }^{+}\to e^{+}\gamma$ using free positive muon decays at rest, the emitted electron and photon in ${\mu }^{-}\to e^{-}\gamma$ exhibit nonmonochromatic spectra, presenting nontrivial case. We derive the decay rate formula and demonstrate that the potential rate of the process is significant enough to motivate exploration in future muon CLFV experiments.

Experimentally, the doubly charm tetraquark channel $cc\overline{q}\overline{q}$ with $q=u$, $d$ features an exotic hadron, $T_{cc}$, with isospin $I=0$ near the $D{D}^{*}$ threshold, while no peak was observed for $I=1$. We present a lattice QCD study of this channel with $I=1$, $J^P=1^{+}$, and $m_{\pi }\simeq 280\mathrm{MeV}$. Finite-volume energies calculated across five charm quark masses consistently feature a positive energy shift with respect to noninteracting energies, indicating repulsive interaction at energies near the threshold. These energies are used to compute the $D{D}^{*}$ scattering amplitude using both the standard Lüscher method and the recently proposed effective field theory-based approach in the plane wave basis, which incorporates the long-range interactions and the left-hand cut. Both analyses render a small negative scattering length and a scattering amplitude that does not feature any poles in the energy region near the $D{D}^{*}$ threshold, in line with the LHCb results. We identify that the Wick contraction, resembling $t$-channel isovector-vector meson exchanges between $D$ and $D^{*}$, plays a key role in distinguishing between the $I=0$ and $I=1$ channels, leading to repulsion in the $I=1$ and attraction in the $I=0$ channel.