Hermiticity is usually treated as a foundational axiom of quantum mechanics, guaranteeing real spectra and unitary time evolution. In this work we argue that Hermiticity is more naturally understood as a symmetry law as a consequence of the global conservation of an inner-product current. We show that in spacetimes admitting complete Cauchy surfaces without boundary flux, this conservation reduces to the familiar condition $H^{†}=H$ in the canonical inner product. However, in the presence of causal horizons—most strikingly in black hole geometries—this conservation law is obstructed for restricted observers. Tracing over inaccessible degrees of freedom inevitably yields completely positive trace-preserving dynamics with an effective non-Hermitian generator. Using quantum thermodynamics and the monotonicity of relative entropy, we demonstrate that the generalized second law may be reinterpreted as an entropy balance compensating precisely for the flux of inner-product charge through the horizon. The structure of Einstein’s equations, via the Bianchi identity and the Raychaudhuri focusing equation, provides the geometric mechanism underlying this balance. We also show that black hole ringdown could be a realistic observational probe for this idea, with it also being an avenue to provide quantitative upper bounds on the strength of horizon-induced inner-product flux. In this way, gravity, entropy production and effective non-Hermiticity are unified under a single structural principle, with Hermiticity emerging as the special case of globally conserved inner-product symmetry.

The inflationary Lyth bound relates the primordial tensor amplitude to the inflaton field excursion. In ekpyrotic, bouncing, and cyclic cosmologies, there is no analogous universal tensor-to-field-distance relation because scalar and tensor perturbations depend on entropy conversion, matching through the bounce, and the specific mechanism that violates or evades the null energy condition. Here, we propose a phase-resolved criterion for the accumulated scalar field trajectory length in a noninflationary smoothing history. The quantity constrained in this study is not, in general, the geodesic distance between the initial and final field-space points. Rather, it is the invariant path length accumulated along the actual cosmological trajectory. Therefore, the resulting inequalities should be understood as sufficient, conservative trajectory length criteria for small-field control, not as model-independent necessary exclusions based on geodesic distance swampland reasoning. We also impose Belinski-Khalatnikov-Lifshitz (BKL) anisotropy suppression as an additional constraint on the ekpyrotic phase. In the canonical phase of the ekpyrotic contraction, we recover the known small-field scaling and embed it in a total trajectory length budget inequality. We impose three requirements: a BKL anisotropy suppression that is parametrized separately, a phenomenological cutoff-corrected distance budget inspired by tower of states logic, and observational conversion windows from residual isocurvature and non-Gaussianity. Furthermore, we propose a new master formula that provides a conditional lower limit on the value of the parameter ${\epsilon }_{\mathrm{ek}}$ that depends on the remaining distance available after conversion and the cosmological bounce. We also derive a curvature constraint for scale-invariant entropy perturbations in curved field space which shows that the small total distance and the observed red tilt seem to indicate ultrafast-roll ekpyrosis, sharp turns, short or strongly modified bounces, and/or significant negative sectional curvature of the scalar manifold. Finally, we demonstrate methods for testing the distance budget against observational data. Examples include $n_s$ running, primordial non-Gaussianity, isocurvature, a stochastic gravitational waves background, and late-time dark energy distance constraints. The observational discussion is organized into explicit diagnostic maps, which are used to identify and analyze specific features and patterns in the data. We also apply the formalism to exponential and cyclic ekpyrotic scalar field potentials, providing a mechanism-resolved interpretation of the bounce or crossover contribution for several specific realizations.

We present a unified study of scalar, vector, and tensor quasinormal modes (QNMs) of Schwarzschild black holes corrected by a Gauss-Bonnet (GB) term in higher dimensions. Using a high-precision Chebyshev spectral method, we map the QNM spectra across $D\in \{5,6,7,8,10,11,12,26\}$ well beyond the regime where sixth-order Wentzel-Kramers-Brillouin and characteristic-integration techniques remain reliable. Across the three spin sectors, we find several robust signatures of higher-curvature dynamics: the appearance of overdamped purely imaginary modes, nonmonotonic behavior in the real parts of higher overtones, and a strong amplification of the dimensionless QNM frequencies in string-motivated dimensions. In the scalar and vector sectors, we uncover an exact isospectrality between the scalar monopole ($\ell =0$) and vector dipole ($\ell =1$) at vanishing GB coupling, and we provide an analytic proof based on a Darboux factorization of the corresponding Hamiltonians. In the tensor sector, we obtain the first numerical confirmation of the long-predicted instability in six dimensions; its onset is sharply captured by the Cohn-Calogero bound and leads to the mass threshold $GM\le 158.1{\alpha }^{3/2}$. No analogous instability is found for $D\ge 7$, and no tensor isospectrality occurs. Converting the dimensionless frequencies to physical units suggests that the amplified modes in higher dimensions may enter the sensitivity window of future space-based detectors such as DECIGO. The merged analysis provides a comprehensive benchmark for QNMs in Einstein-Gauss-Bonnet gravity and highlights the limitations of standard approximation schemes in the strong-coupling and high-overtone regimes.

Dynamical tidal deformations play a crucial role in the gravitational waves emitted by binary neutron-star systems during their late inspiral. In this work, we systematically explore how relativistic (dynamical and dissipative) tidal deformations depend on the internal structure of a neutron star using two analytic classes of equations of state. The first class is a nucleonic model that is parametrized by nuclear-physics observables, such as the symmetry energy coefficients and saturation properties. The second class is a toy model of quark matter, the MIT bag model. To model tidal dissipation, we self-consistently include contributions from weak-interaction-driven bulk-viscous effects while considering both the nucleonic and the quark-matter equations of state. The dissipative tide is sensitive to frequency and temperature, but its magnitude, as predicted by weak-interaction-driven bulk-viscous effects, is too small (within the equation-of-state models studied here) to be detectable by current or future observations. However, we find that the (conservative) dynamical tidal response function depends strongly on the slope of the symmetry energy and on higher-order coefficients of the symmetry energy. This indicates that the (conservative) dynamical tide is sensitive to higher-order coefficients, motivating a dedicated parameter-estimation study to assess how well they can be constrained.

We investigate the scale dependence of the primordial power spectrum by combining Planck, ACT DR6, SPT-3G, and eBOSS Lyman-$\alpha$ forest data, extending sensitivity to smaller comoving scales than those probed by the cosmic microwave background (CMB) alone. Within a parametrization based on a Taylor expansion around the pivot scale, we constrain the running of the spectral index ${\alpha }_s$ and its running ${\beta }_s$. By using eBOSS likelihoods exhibiting a suppression of small-scale power either in amplitude or spectral index, we show that the latter can be accommodated by correlated variations of $({\alpha }_s,{\beta }_s)$, leading to a preference for nonzero running. We show that inflationary potentials with localized features—such as Gaussian dips, bumps, or axion-monodromy modulations—can reproduce the inferred scale dependence while remaining compatible with current CMB constraints. We release the public pipe code to enable systematic tests of inflationary potentials against current CMB datasets.

domain-wall (DW) networks are known to approach a relativistic scaling regime on fixed radiation- and matter-dominated backgrounds, forming the basis of the no-frustration conjecture. However, this picture assumes that the defect network remains gravitationally subdominant. We investigate the self-consistent evolution of DWs by coupling the velocity-dependent one-scale model to the Friedmann equation and radiation energy transfer. The resulting autonomous system allows the cosmic expansion history to evolve dynamically rather than being imposed externally. We demonstrate analytically that gravitational backreaction qualitatively changes the phase-space structure: the radiation-era scaling solution, which is a stable attractor on a fixed background, becomes a saddle once the expansion rate is promoted to a dynamical degree of freedom. Furthermore, we establish that no stable fixed point exists within the physical phase space. Consequently, the scaling regime survives only as a transient stage, and all trajectories are driven toward a wall dominated and kinematically frustrated state in which the walls freeze in comoving coordinates. Our results demonstrate that the scaling attractor is not preserved in self-gravitating DW networks and reveal the generic late-time frustration dynamics of wall domination.

The neutron–to–mirror-neutron transitions in neutron stars could possibly result in significant effects. In this work, we show that collisional decoherence entails exponential relaxation in lieu of oscillations. Decoherence is a great many orders of magnitude faster than the expected oscillations. The admixture of mirror neutrons at all times remains very small with respect to the ordinary-neutron component.

We develop a framework for testing quantum gravity through the stochastic gravitational-wave background produced by evaporating near-Planck-mass primordial black holes. Because gravitons freestream from the emission region without rescattering, they preserve a direct spectral record of the black-hole temperature–mass relation $T(M)$, a relation that is erased for all other Hawking-radiated species by rapid thermalization. We translate six representative phenomenological beyond-semiclassical frameworks (the generalized uncertainty principle, loop quantum gravity, noncommutative geometry, asymptotic safety, string/Hagedorn physics, and tunneling backreaction) into distinct $T(M)$ parameterizations and compute the resulting gravitational-wave spectra numerically within a hybrid semiclassical-phenomenological framework. Modifications that suppress $T(M)$ shift the spectral peak by up to 10 decades in frequency, in some cases into the sensitivity bands of next-generation interferometers or resonant-cavity detectors, while models imposing a hard evaporation cutoff produce distinctive peak morphologies that distinguish between phenomenological classes of modified evaporation. We further discuss the impact of different choices for post-inflationary conditions in the very early Universe and note that breaking the remaining cosmological degeneracies and connecting these signatures to specific quantum-gravity theories requires complementary observables. We find that the relative spectral displacement between the standard Hawking prediction and any modified model is cosmology-independent, and hence spectral shape rather than absolute peak frequency provides the cleanest probe of Planck-scale physics.

We present a systematic study of the masses of light excited $q\overline{q}$ mesons using quantum chromodynamics (QCD) sum rules at next-to-leading order (NLO). To probe excited states, we construct several interpolating currents with covariant derivatives inserted. The calculation is carried out up to dimension-8 condensates, including NLO perturbative and $m⟨\overline{q}q⟩$ corrections. Employing Gaussian sum rules, we obtain several $J^P=2^{\pm }$ nonets with masses that agree well with experiments. Several $J=0$, 1 states compatible with experiments are also obtained using both Gaussian and Laplace sum rules. In particular, the $J^{PC}=2^{++}$ current couples to two distinct $2^{++}$ resonances. This work demonstrates the efficacy of operators with covariant derivatives for studying excited hadrons.

In this paper, we derive the upper bounds on the coupling of axionlike particles (ALPs) with photon as a function of the mass by considering axion-photon conversion in the Crab Nebula. Previous studies have not considered the influence of the magnetic field within the Crab Nebula. The magnetic field plays a crucial role through the synchrotron self-Compton process, in which high-energy electrons produce synchrotron radiation that is subsequently upscattered by the same electrons via inverse Compton scattering to generate $\gamma$ rays. Therefore, neglecting the magnetic field in modeling leads to theoretical inconsistencies. In this work, we investigate the significance of the magnetic field effect and demonstrate that even differences in magnetic field modeling can substantially alter the conversion probability. We thus, for the first time, point out that proper consideration of the magnetic field is essential in ALP searches using $\gamma$ rays from the Crab Nebula. The resulting constraints reach up to a coupling of $g_{a\gamma \gamma }\lesssim 1\times {10}^{-11}{\mathrm{GeV}}^{-1}$ for ALP masses in the range ${10}^{-10}\mathrm{eV}\lesssim m_a\lesssim {10}^{-6}\mathrm{eV}$.

We investigate $2P\text{−}1F$ mixing in charmonium, focusing on the close-in-mass ${\chi }_{c2}(2P)$ and ${\chi }_{c2}(1F)$ states. The conventional tensor force yields negligible mixing, motivating the inclusion of coupled-channel effects. Our unquenched calculation reveals sizable mixing angles of 7.5° and 15.4°. We predict the corresponding two-photon and two-gluon decay widths as key observables for experimental verification. Additionally, we discuss the production of these two $2P\text{−}1F$ mixed states of charmonium via $\gamma \gamma$ fusion. Current data are insufficient to determine the mixing, highlighting the need for precise future measurements to resolve this aspect of charmonium spectroscopy.

The Wigner distributions (WDs) in boost-invariant longitudinal space for unpolarized, longitudinally polarized, and linearly polarized gluons within a proton are presented in the framework of the light-front gluon spectator model inspired by AdS/QCD. The boost-invariant longitudinal space defined by the coordinate $\sigma =\frac{1}{2}{b}^{-}{P}^{+}$, can be accessed through the Fourier transformation over skewness $\xi$ to the gluon-gluon correlator of generalized transverse momentum dependent distributions (GTMDs). The model results for gluon WDs in $\sigma$-space show an oscillatory behavior analogous to the diffraction scattering of a wave in optics. The diffraction pattern is more sensitive to the momentum fraction $x$ and passively varies with the total energy transfer to the electron-proton scattering $-t$, both of which are analogous to an effective slit width. The leading-twist gluon WDs in the impact-parameter space and their skewness sensitivity are investigated extensively for unpolarized, longitudinally polarized, and transversely polarized protons. The gluon spin-orbital angular momentum correlation is also reported and compared with existing models and lattice results.

We consider the dynamics of an expanding superfluid modeled by Mueller-Israel-Stewart theory coupled to a complex scalar field with a $U(1)$ symmetry that is spontaneously broken. This is a manageable theoretical setting for explorations of the chiral phase transition of expanding quark-gluon plasma. We study the late proper-time behavior of Bjorken flow in this physical system and find that asymptotic solutions can be expressed as a transseries of a novel form, which contains factors like ${\tau }^{-\ln \tau }$. This transseries describes how the information encoded in the initial data is diluted in the course of dissipative evolution. These solutions retain memory of the symmetry-breaking transition and describe two qualitatively different late-time behaviors of the dynamical variables, depending on condensate relaxation rate: either a purely damped falloff or damped oscillations. The possibility that such oscillations could be imprinted in the observed outcomes of heavy ion collision experiments is the main physical insight that follows from our analysis.

A search is performed for a new resonance $X$ decaying into a Higgs boson and a new scalar boson $Y$ ($HY$) including the case where $Y$ is assumed to be a second Higgs boson ($HH$), using proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. This study performs a comprehensive exploitation of the $bbZZ$ events, encompassing the following decay topologies. One $H$ candidate is identified through its decay into a bottom quark-antiquark pair, while the other $H$ or the $Y$ candidate is selected through its decay into a pair of $Z$ bosons. One $Z$ boson is required to decay leptonically and the other, to decay into a pair of quarks or neutrinos. Events of interest are categorized based on the Lorentz boosts of the hadronically decaying $H$ and $Z$ bosons. Machine-learning-based discriminants, together with the reconstructed resonance mass, are employed across the different categories to separate signal from backgrounds, and their corresponding distributions are included in a simultaneous fit. No significant deviations from the standard model predictions are observed. Upper limits at the 95% confidence level are set on the $HY$ and $HH$ production cross sections. For $HY$ production, the upper limit on the cross section of the process $pp\to X\to HY\to bbZZ$ ranges from 500 to 5 fb, with the most stringent constraints achieved for high-mass $X$ resonances and $Y$ masses near the threshold for decay into a pair of massive vector bosons. This is comparable to the sensitivity achieved in other analyses, which focus on $H$ decays to $\gamma \gamma$ or $\tau \tau$ and $Y$ decays into a pair of bottom quarks or massive vector bosons. For resonant $HH$ production, the upper limit on the cross section of $pp\to X\to HH$ production is 1 pb for a high-mass resonance.

In recent years, many interesting works providing a topological description for black hole (BH) properties have appeared in the literature. In particular, in this framework BHs correspond to topological defects in an enlarged (off shell) parameter space, with an associated total topological charge. In gauge/gravity duality the transition from the confined to the deconfined phase is mapped into the dominance of a BH phase on the gravity side. Here we show, using a holographic anti–de Sitter (AdS)/QCD model, that the introduction of an energy scale in AdS space results in a change in the topological class. Such a modification corresponds to the existence of confined and deconfined phases, separated by a Hawking-Page transition at a finite critical temperature.

In dynamically formed binaries, the spins of the black holes tend to be misaligned with the system’s orbital angular momentum. This causes the spins to precess and leads to an asymmetric emission of gravitational waves. The resulting gravitational-wave multipole asymmetries directly source the recoil of the remnant black hole and are the critical element in fully describing precession. Recoil and precession are of significant astrophysical importance, but multipole asymmetries contribute only minimally to the overall signal strength. Consequently, most current gravitational-wave models either do not incorporate asymmetries at all, or only consider the dominant ones. Here we highlight the importance of subdominant multipole asymmetries for an accurate recoil velocity calculation and discuss their detectability with third generation detectors. Neglecting subdominant asymmetries leads to velocity differences of up to $210\mathrm{km}/\mathrm{s}$ and can, in particular, introduce systematic biases in the inference of masses and the spin geometry. We further discuss universal characteristics of subdominant multipole asymmetries in order to prepare the ground for potential future asymmetry models. In the inspiral regime, the average antisymmetric frequencies can be described by a multiple of the orbital frequency. During ringdown, however, they become equal to their corresponding symmetric frequencies.

The oscillation modes of stars play an important role in observations, and on the understanding of stellar stability properties. The role of viscosity in the oscillation modes of compact stars has been so far understood very loosely only, in absence of a well-posed framework. We use recent breakthroughs in the formulation of a causal and stable theory of relativistic hydrodynamics to study oscillation modes of neutron stars. We characterize the axial spectrum of compact stars and uncover new, viscosity-driven families of modes, without a perfect fluid counterpart. Our results show mode avoidance in some of these families, and a spectrum of long-lived modes, whose role in astrophysical, dynamical processes is yet to be understood.

Numerical-relativity simulations with nontrivial matter configurations require initial data that satisfy the Hamiltonian and momentum constraints of the Einstein equations. We construct constraint-satisfying scalar-field initial data using the extended conformally flat condition (XCFC) formalism, in which the matter variables are conformally rescaled and an auxiliary vector field is introduced. In doing so, we overcome the issues of local uniqueness and convergence of the solutions that arise in the second-order elliptic equations associated with the constraints. Using an iterative solver method, we demonstrate the convergence of the XCFC approach to a solution for several scalar-field matter systems. Those include Gaussian-like profiles, topological torus configurations, and equal-mass boson star binaries. In particular, for the latter case, it is common to employ the superposition of two isolated boson star solutions in order to build the initial data. We show that our formalism significantly improves upon a superposition approach by generating genuinely constraint-satisfying initial data for boson star binaries.

We investigate the geodesic structure of realistic static and spherically symmetric spacetimes embedding neutron stars in metric $f(R)$ gravity, focusing on the quadratic Starobinsky model $f(R)=a{R}^2$ with $a<0$. Neutron-star solutions are obtained by numerically solving the modified Tolman-Oppenheimer-Volkoff system for several realistic equations of state. Such solutions are then matched consistently to the exterior vacuum geometry by enforcing the full set of junction conditions required in metric $f(R)$ theories. Using an effective potential approach, we show that stable circular orbits appear in discrete radial bands separated by forbidden regions, with a dominant principal band of stability that depends sensitively on the stellar central pressure, the equation of state, and the magnitude of the parameter $|a|$. Outside the stable bands, massive particles can have bound but unstable precessing trajectories as well as unbounded motions. On the other hand, for null geodesics, we find no evidence for photon spheres outside the neutron star within the parameter range studied.

We demonstrate that primordial black holes (PBHs) lighter than ${10}^9\mathrm{g}$, which evaporated before the big bang nucleosynthesis, can induce significant isocurvature perturbations due to their biased clustering amplitude and the branching ratio of the Hawking radiation differing from the abundance ratio. By leveraging the upper bound on the isocurvature perturbations from the cosmic microwave background anisotropies reported by the Planck collaboration, we derive a new upper bound on the abundance of these light PBHs in the presence of primordial non-Gaussianity as a working example.