We explore the quantum superposition of boundary conditions in the context of the Poincaré patch of the two-dimensional anti–de Sitter space. Focusing on Robin (mixed) boundary conditions, we investigate the response function of the Unruh-DeWitt (UDW) detector interacting with two or more scalar fields, each respecting a different boundary condition. The role of this quantum superposition is twofold: (i) it may represent different fields propagating on the same spacetime and interacting with an UDW detector or (ii) it may describe an UDW detector on a superposition of spacetimes, each one with an inequivalent propagating field.

We provide a detailed decomposition of Wigner’s particles, defined as unitary irreducible representations of the Poincaré group, in terms of unitary representations of its Lorentz subgroup. As pointed out before us, this decomposition only involves Lorentz representations belonging to the principal continuous series, and further underpins the connection between scattering amplitudes and conformal correlation functions discussed in the context of celestial holography. We provide very explicit formulas for the decomposition of particles of arbitrary mass and (half-)integer spin and for any spacetime dimension. We emphasize that this decomposition is unique and comes equipped with a specific inner product on the corresponding Hilbert space. We also confirm that unitary translations mix Lorentz representations within the principal continuous series only, as required. Implications to the celestial holography program are indicated.

A finite duration of cosmic inflation can result in features ${\mathcal{P}}_{\mathcal{R}}(k)=|{\alpha }_k-{\beta }_k{\mathrm{e}}^{\mathrm{i}{\delta }_k}{|}^2{\mathcal{P}}_{\mathcal{R}}^{(0)}(k)$ in the primordial power spectrum that carry information about a quantum gravity phase before inflation. While the almost scale-invariant power spectrum ${\mathcal{P}}_{\mathcal{R}}^{(0)}$ for the quasi-Bunch-Davies vacuum is fully determined by the inflationary background dynamics, the Bogoliubov coefficients ${\alpha }_k$ and ${\beta }_k$ for the squeezed vacuum depend on new physics beyond inflation and have been used to produce phenomenological templates for the features. The phase ${\delta }_k$ vanishes in de Sitter space and therefore is often neglected, but it results in nontrivial effects in quasi–de Sitter inflationary geometries. Here we consider a large class of effective theories of inflation and provide a closed-form expression for ${\delta }_k$ and for the fully expanded power spectrum up to next-to-next-leading order (N2LO) in the Hubble flow expansion. In particular, for the Starobinsky model of inflation we find that this relative phase can be expressed in terms of the scalar tilt $n_{\mathrm{s}}$ as ${\delta }_{k*}=\frac{\pi }{2}(n_{\mathrm{s}}-1)-\frac{\pi }{4}(n_{\mathrm{s}}-1{)}^2\ln (k/k_{*})$. The relative phase results in a negative shift and a running frequency that have been considered in the most studied phenomenological templates for primordial features, thus providing precise theoretical predictions for upcoming cosmological observations.

Black hole solutions in general scalar-tensor theories are known to permit hair, i.e., nontrivial scalar profiles and/or metric solutions different from the ones of general relativity (GR). Imposing that some such solutions—e.g., Schwarzschild or de Sitter solutions motivated in the context of black hole physics or cosmology—should exist, the space of scalar-tensor theories is strongly restricted. Here we investigate precisely what these restrictions are within general quadratic/cubic higher-order scalar-tensor theories for stealth solutions, whose metric is given by that in GR, supporting time-dependent scalar hair with a constant kinetic term. We derive, in a fully covariant approach, the conditions under which the Euler-Lagrange equations admit all (or a specific set of) exact GR solutions, as the first step toward our understanding of a wider class of theories that admit approximately stealth solutions. Focusing on static and spherically symmetric black hole spacetimes, we study the dynamics of linear odd-parity perturbations and discuss possible deviations from GR. Importantly, we find that requiring the existence of all stealth solutions prevents any deviations from GR in the odd-parity sector. In less restrictive scenarios, in particular, for theories only requiring the existence of Schwarzschild(–de Sitter) black holes, we identify allowed deviations from GR, derive the stability conditions for the odd modes, and investigate the generic deviation of a nontrivial speed of gravitational waves. All calculations performed in this paper are reproducible via companion Mathematica notebooks.

It has been shown that black hole quasinormal modes are subject to spectral instability, typically triggered by metric perturbations. These perturbations, which can introduce a minor bump in the effective potential of the wave equation, give rise to a novel branch of asymptotic quasinormal modes, dubbed the echo modes, which lie mainly parallel to the real frequency axis. This study explores the evolution of the echo modes and their interplay with the outward spiral motion observed in low-lying quasinormal modes. As the bump in the effective potential moves away from the central black hole, the echo modes collectively shift toward the real axis, with the spacing between successive modes decreasing uniformly. This collective motion occurs simultaneously with the spiral of the low-lying modes until the echo modes eventually take over the fundamental quasinormal mode. In the time domain, such a takeover coincides with a transition point for the temporal waveform, where the distinction between the original black hole’s ringdown and the echoes becomes clear. This marks a transition in the characteristics of the waveform from primarily damped oscillations, dominated by the damping rate of the fundamental mode, to echo waves, characterized by periodic echo pulses. We argue that this phenomenon is universal by employing analytical and numerical analyses. We first elucidate our arguments using explicit but simplified toy models, where the effective potential barriers are disjoint. The derivations are then generalized to scenarios where perturbations are introduced on top of a black hole metric with a continuous effective potential. The observational implications, particularly the causality dilemma, are elaborated. We show that the echo modes can be extracted by applying the Fourier transform to ringdown waveforms, which can be important for gravitational wave observations.

Analog gravity systems have the unique opportunity to probe theoretical aspects of black hole physics in a controlled laboratory environment that one cannot easily observe for astrophysical black holes. In this work, we address the question of whether one could use controlled initial perturbations to excite the black hole ringdown and infer the effective black hole metric. Using a theory-agnostic ansatz for the effective metric described by the Rezzolla-Zhidenko metric and evolving perturbations on that background, we quantify with Bayesian analysis what regions of the effective spacetime could be constrained in experiments. In contrast to standard ringdown analyses based on quasinormal mode extraction, a laboratory-controlled setup, in combination with our framework, allows one to model the entire signal, including the prompt response and possible effects of late-time tails. Therefore, it has the intriguing advantage of not relying on start and end times when the superposition of quasi-normal modes is a good signal approximation. It also avoids the nontrivial question of how many modes are present. We demonstrate that this approach is feasible in principle and discuss opportunities beyond this study.

Understanding the characteristics of the remnant black hole formed in a binary black hole merger is crucial for conducting gravitational wave astronomy. Typically, models of remnant black holes provide information about their mass, spin, and kick velocity. However, other information related to the supertranslation symmetries of the BMS group, such as the memory effect, is also important for characterizing the final state of the system. In this work, we build a model of the BMS transformation that maps a binary black hole’s inspiral frame to the remnant black hole’s canonical rest frame. Training data for this model are created using high-precision numerical relativity simulations of quasicircular systems with mass ratios $q\le 8$ and spins parallel to the orbital angular momentum with magnitudes ${\chi }_1$, ${\chi }_2\le 0.8$. We use Gaussian process regression to model the BMS transformations over the three-dimensional parameter space $(q,{\chi }_1^z,{\chi }_2^z)$. The physics captured by this model is strictly nonperturbative and cannot be obtained from post-Newtonian approximations alone, as it requires knowledge of the strong nonlinear effects that are sourced during the merger. Apart from providing the first model of the supertranslation induced by a binary black hole merger, we also find that the kick velocities predicted using Cauchy-characteristic evolution waveforms are, on average, $\sim 5\%$ larger than the ones obtained from extrapolated waveforms. Our work has broad implications for improving gravitational wave models and studying the large-scale impact of memory, such as on the cosmological background. The fits produced in this work are available through the python package surfinbh under the name nrsur3dq8bmsremnant.

The minimal warm inflation scenario proposed in [K. V. Berghaus et al., Warm inflation with the standard model, arXiv:2503.18829.]—featuring an axionlike inflaton coupled to Standard Model (SM) gluons via the standard interaction $\varphi G\tilde{G}$—offers a compelling bridge between inflationary dynamics and SM particle content. While the model retains only the inflaton as a beyond-SM field, its original analysis relied on some approximate treatments of warm inflation’s (WI) dynamics. Here, we revisit this scenario using wi2easy, a precision computational tool for WI dynamics [G. S. Rodrigues and R. O. Ramos, wi2easy: Warm inflation dynamics made easy, arXiv:2504.17760.], to rigorously evaluate the model’s viability and full range of model’s parameters compatible with the observational parameters. Overall, we find that the results of Berhaus et al. hold, but with significant differences in the weak and strong dissipative regimes of WI.

The Hubble tension, a significant discrepancy between the Hubble constant ($H_0$) values derived from early-time [cosmic microwave background (CMB) and baryon acoustic oscillations] and late-time [Cepheid-calibrated Type Ia Supernovae (SNe Ia)] measurements, remains a major challenge in cosmology. Traditional attempts to resolve this tension have struggled to maintain consistency with dynamical and geometrical probes at redshifts $0.01<z\lesssim 2.5$. We explore a novel model introducing new degrees of freedom in local physical laws affecting calibrators like Cepheids and Type Ia Supernovae within a distance of $d\lesssim 50\mathrm{Mpc}$ ($z\lesssim 0.01$). Specifically, we incorporate a gravitational transition causing a change in the gravitational constant ($G$) at a specific distance, affecting the Cepheid period-luminosity relation and the absolute magnitude of SNe Ia. We verify the inverse scaling of SN luminosity $L$ with Chandrasekhar mass $M_C$ in a changed $G$ scenario, as predicted using a semianalytical model in a recent theoretical study [Type Ia supernovae, standardizable candles, and gravity, Phys. Rev. D 97, 083505 (2018).]. Fixing $\mathrm{\Delta }G/G\approx 0.04$, our model naturally resolves the Hubble tension, yielding a best-fit $H_0$ value consistent with the Planck measurement, even without using Planck data. This approach suggests a potential resolution to the Hubble tension by aligning $H_0$ with high-redshift CMB measurements.

We investigate whether the pre-big-bang (PBB) scenario from string cosmology can explain the stochastic gravitational wave background signal reported in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 15-yr dataset. Using Bayesian analysis techniques, we constrain the key parameters of the PBB model by comparing its theoretical predictions with the observed data. Our analysis yields $\beta =-0.12_{-0.21}^{+0.06}$ (90% credible interval) for the dilaton-dynamics parameter, which lies outside the theoretically allowed range $0\lesssim \beta <3$ with more than $5\sigma$ confidence. Additionally, model comparison strongly favors a simple power-law spectrum over the PBB scenario, with a Bayes factor of approximately 468. These results demonstrate that the PBB scenario, in its current formulation, cannot adequately explain the NANOGrav observations, highlighting the need for either significant modifications to the model or alternative explanations for the observed signal.

The number density and redshift evolution of optically selected galaxy clusters offer an independent measurement of the amplitude of matter fluctuations, $S_8$. However, recent results have shown that clusters chosen by the redMaPPer algorithm show richness-dependent biases that affect the weak lensing signals and number densities of clusters, increasing uncertainty in the cluster mass calibration and reducing their constraining power. In this work, we evaluate an alternative cluster proxy, outskirt stellar mass, $M_{\mathrm{out}}$, defined as the total stellar mass within a [50, 100] kpc envelope centered on a massive galaxy. This proxy exhibits scatter comparable to redMaPPer richness, $\lambda$, but is less likely to be subject to projection effects. We compare the Dark Energy Survey Year 3 redMaPPer cluster catalog with a $M_{\mathrm{out}}$ selected cluster sample from the Hyper-Suprime Camera survey. We use weak lensing measurements to quantify and compare the scatter of $M_{\mathrm{out}}$ and $\lambda$ with halo mass. Our results show $M_{\mathrm{out}}$ has a scatter consistent with $\lambda$, with a similar halo mass dependence, and that both proxies contain unique information about the underlying halo mass. We find $\lambda$-selected samples introduce features into the measured $\mathrm{\Delta }\mathrm{\Sigma }$ signal that are not well fit by a log-normal scatter only model, absent in $M_{\mathrm{out}}$ selected samples. Our findings suggest that $M_{\mathrm{out}}$ offers an alternative for cluster selection with more easily calibrated selection biases, at least at the generally lower richnesses probed here. Combining both proxies may yield a mass proxy with a lower scatter and more tractable selection biases, enabling the use of lower mass clusters in cosmology. Finally, we find the scatter and slope in the $\lambda -M_{\mathrm{out}}$ scaling relation to be $0.49\pm 0.02$ and $0.38\pm 0.09$.

We construct a model for stationary and axisymmetric black hole magnetospheres by solving the vacuum Maxwell equations in Kerr backgrounds. The poloidal magnetic field is generated by a toroidal electric current in a thin disk on the equatorial plane with an inner edge, and the poloidal electric field is induced due to the black hole spin. We assume a current distribution whose direction reverses at a radius on the disk. The magnetospheric structure is divided into the inner region and the outer one due to the current reversal. In the inner region, some magnetic field lines connect the black hole and the disk, and others surround the inner edge of the disk. In the outer region, the field lines connect the disk and infinity. We investigate the black hole spin dependence of the magnetospheric structure. In the magnetosphere around the Kerr black hole, the electric fields are generated by the black hole spin. In our model, the charge distribution is induced on the disk and the event horizon. Except near the black hole, the electric field strength is proportional to the black hole spin, while the direction of the electric field remains almost the same regardless of the spin. On the other hand, the electromagnetic field near the event horizon strongly depends on the spin. In the maximally rotating case, the magnetic field lines are expelled from the event horizon and the electric equipotential surface coincides with the horizon.

We explore the big-bang nucleosynthesis (BBN) constraint on heavy neutrino that is a mixture of gauge-singlet fermion and active neutrinos in the Standard Model. We work in the minimal model with only two parameters, the heavy neutrino mass $m_4$ and the mixing parameter $|U_{a4}{|}^2$, where $a=e$, $\mu$, or $\tau$ stands for the active neutrino flavor. We show that both the early Universe production mechanism and decay products of the heavy neutrino are determined by $m_4$ and $|U_{a4}{|}^2$, with little room for further assumptions. This predictability allows us to present a portrait of the entire BBN excluded parameter space. As a novel result, we derive the lower boundary of the BBN exclusion in the $|U_{a4}{|}^2$ versus $m_4$ parameter space. Our analysis includes various effects including temporary matter domination, energy injections in the form of charged mesons, photons, and light neutrinos. The BBN constraint is complementary to the terrestrial search for heavy neutrinos (heavy neutral leptons) behind the origin of neutrino masses and a portal to the dark sector.

In this paper, we investigate the semileptonic decays $B_c\to {\eta }_c\ell {\overline{\nu }}_{\ell }$ using the quantum chromodynamics (QCD) sum rules within the framework of Standard Model (SM). We further explore the potential to probe signatures of new physics (NP) beyond the SM through these decays. First, we derive the $\xi$-moments $⟨{\xi }_{2;{\eta }_c}^n⟩$ of the ${\eta }_c$-meson leading-twist distribution amplitude ${\varphi }_{2;{\eta }_c}$ using the QCD sum rules within the background field theory. Considering contributions from the vacuum condensates up to dimension-six, the first two nonzero $\xi$-moments at the scale of 4 GeV are found to be $⟨{\xi }_{2;{\eta }_c}^2⟩=0.103_{-0.009}^{+0.009}$ and $⟨{\xi }_{2;{\eta }_c}^4⟩=0.031_{-0.003}^{+0.003}$. Using these moments, we then fix the Gegenbauer expansion series of ${\varphi }_{2;{\eta }_c}$ and apply it to compute the $B_c\to {\eta }_c$ transition form factors (TFFs) using QCD light cone sum rules. Second, we extrapolate those TFFs to physically allowable $q^2$-range via a simplified series expansion, and we obtain $R_{{\eta }_c}{|}_{\mathrm{SM}}=0.308_{-0.062}^{+0.084}$. Furthermore, we explore the potential impacts of various NP scenarios on $R_{{\eta }_c}$. Specifically, we compute the forward-backward asymmetry ${\mathcal{A}}_{\mathrm{FB}}(q^2)$, the convexity parameter ${\mathcal{C}}_F^{\tau }(q^2)$, and the longitudinal and transverse polarizations ${\mathcal{P}}_L(q^2)$ and ${\mathcal{P}}_T(q^2)$ for $B_c\to {\eta }_c$ transitions within both the SM and two types of NP scenarios. Our results contribute to a deeper understanding of $B_c$-meson semileptonic decays and provide insights into the search for the NP beyond the SM.

We present a detailed study of the partial decay widths of a spin-parity resonance $J^P=3/2^{-}$ $N^{*}$ with a mass of $\simeq 2070\mathrm{MeV}$ obtained from the coupled channel $s$-wave vector-baryon $\rho N$, $\omega N$, $\varphi N$, $K^{*}\mathrm{\Lambda }$, and $K^{*}\mathrm{\Sigma }$ dynamics. This state, which couples strongly to the $K^{*}\mathrm{\Sigma }$ channel, corresponds to a nucleon with a hidden strange quark content, in analogy to the $P_c$ states discovered by the LHCb Collaboration, and we denote it as $P_s(2080)$. A state with such a nature can decay to vector-baryon, pseudoscalar-baryon, and pseudoscalar-baryon resonance channels, involving triangular loops in the latter two cases. As we will show, the partial decay widths to pseudoscalar-baryon resonance channels, like $\pi N^{*}(1535)$, $\pi N^{*}(1650)$, $K\mathrm{\Lambda }(1405)$, are comparable to those related to ground state baryons in the final state, like $\pi N$, $\eta N$, $K\mathrm{\Lambda }$. In this way, reactions involving such lighter baryon resonances in the final state can be used as an alternative source of information on the properties of an $N^{*}$ with hidden strangeness.

The D3-D7 holographic model is used to describe the core of the hybrid star, composed by quark matter, while its crust is modeled from a hadronic relativistic mean field (RMF) model capable of reproducing low-energy nuclear physics data as well as some astrophysical observations. The D3-D7 brane configuration and the RMF model lead to an equation of state that is used to solve the Tolman-Oppenheimer-Volkoff equations. For different model parameters, the mass-radius diagram is presented. The conditions for the dynamic stability of stellar configurations are discussed, considering the radial oscillation criterion for hybrid stars with slow phase transitions. Strikingly, it is shown that the models generate stable star configurations with a core of quarks. We compare our results with NICER observational data for the pulsars PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$ and show that the compact stars generated from this method fall within the corresponding observational regions.

We propose a novel pathway to generate the electroweak scale (EW) via nonperturbative dynamics of a dark gauge sector based on the SU(N) gauge group. Imposing the scale invariance of the theory, we investigate the electroweak symmetry breaking (EWSB) which is triggered dynamically via the condensation of gauge fields. Instead of the usual dimension-4 triggered breaking, a dimension 6 term (with Wilson coefficient compatible with Standard Model Effective Field Theory (SMEFT) bounds) coupling the Higgs boson and the Yang-Mills field quadratic term in the Lagrangian provides feedback from the gauge to the Higgs sector. We provide a novel method to estimate a nonperturbative EW scale generation using the exact solution of a truncated set of the background equations of motion in Yang-Mills theory in terms of Jacobi elliptic functions and the exact beta-function valid in the strongly coupled regimes via the Dyson-Schwinger approach. Particularly, we find an analytical result for the renormalization group equation (RGE) of the gauge coupling in the $SU(N)$ sector in the strongly coupled regime. The dynamics studied in this paper pave the way to a more realistic model building with possible resolution to the hierarchy problem and, in general, dynamical generation of scales.

The decrease of the chiral pseudocritical temperature $T_{pc}$ with an applied strong magnetic field has been extensively investigated by various QCD low-energy effective models and lattice QCD at the physical point. We find that this decreasing feature may not hold in the case with a weak magnetic field and still depends on quark masses: when the quark masses get smaller, $T_{pc}$ turns to increase with the weak magnetic field. This happens due to the significant electromagnetic scale anomaly contribution in the thermomagnetic medium. We demonstrate this salient feature by employing the Nambu-Jona-Lasinio model with $2+1$ quark flavors including the electromagnetic scale anomaly contribution. We observe that at $(m_{0c},m_{sc})\simeq (2,20)\mathrm{MeV}$ for the isospin symmetric mass for up and down quarks, $m_0$, and the strange quark mass, $m_s$, $T_{pc}$ decreases with the magnetic field if the quark masses exceed the critical values, and increases as the quark masses become smaller. Related cosmological implications, arising when the supercooled electroweak phase transition or dark QCD cosmological phase transition is considered along with a primordial magnetic field, are also briefly addressed.

Charged scalars appear in many motivated extensions beyond the Standard Model. We analyze the constraints on charged scalar pair production via the Drell-Yan process at the Large Hadron Collider and interpret them in terms of weak isospin quantum numbers. Leveraging the experimental limits from existing LHC data and phenomenological recast analyses, we place bounds on the branching ratio of the charged scalar as a function of its mass, electric charge, and isospin. This approach enables us to determine limits on the branching ratios directly from experimental data, without appealing to a specific model. We provide a detailed analysis for singly and doubly charged scalars across various weak isospin scenarios, focusing on decays into leptonic and bosonic final states, and we validate this approach in extended Higgs sectors such as the Higgs triplet model and the Georgi-Machacek model.

We study the finite-temperature behavior of the $Sp(4)$ Yang-Mills lattice theory in four dimensions, by applying the logarithmic linear relaxation algorithm. We demonstrate the presence of coexisting (metastable) phases, when the system is in the proximity of the transition. We measure observables such as the free energy, the expectation value of the plaquette operator and of the Polyakov loop, as well as the specific heat, and the Binder cumulant. We use these results to obtain a high-precision measurement of the critical coupling at the confinement-deconfinement transition, and assess its systematic uncertainty, for one value of the lattice extent in the time direction. Furthermore, we perform an extensive study of the finite-volume behavior of the lattice system, by repeating the measurements for fixed lattice time extent, while increasing the spatial size of the lattice. We hence characterize the first-order transition on the lattice and present the first results in the literature on this theory for the infinite volume extrapolation of lattice quantities related to latent heat and interface tension. Gauge theories with $Sp(4)$ group have been proposed as new dark sectors to provide a fundamental origin for the current phenomenological evidence of dark matter. A phase transition at high temperature, in such a new dark sector, occurring in the early Universe, might have left a relic stochastic background of gravitational waves. Our results represent a milestone toward establishing whether such a new physics signal is detectable in future experiments, as they enter the calculation of the parameters, $\alpha$ and $\beta$, controlling the power spectrum of gravitational waves. We also outline the process needed in the continuum extrapolation of our measurements and test its feasibility on one additional choice of temporal extent of the lattice.