We build an effective field theory of multifield inflationary fluctuations based on the adiabatic perturbation and any number of matter fluctuations in the nonadiabatic sector, without imposing extra symmetries on the latter. Focusing on terms with at most two derivatives in the fields’ fluctuations, we argue that taking the decoupling limit—in which gravitational interactions are neglected—is justified in a quasi–de Sitter spacetime with a slow-varying Hubble scale. With these working hypotheses, we find simple forms of multifield mixings (quadratic order) and interactions (cubic order). We explain how to break degeneracies among various terms, and we compare the predictions of the effective field theory to those of nonlinear sigma models of inflation and a more general multifield Lagrangian in the traditional model approach. We stress that several multifield cubic interactions are dictated by nonlinearly realized spacetime symmetries and are therefore given in terms of parameters already present in the quadratic action. We propose various directions to systematically explore the phenomenology generic to multifield inflation and beyond the lamppost of known models.

A consistency condition of general relativity as an effective field theory in Minkowskian background uniquely fixes the value of the cosmological constant. In two-loop calculations, including the interaction of gravitons with matter fields, it has been shown that this value of the cosmological constant leads to vanishing vacuum energy, under the assumption that the energy-momentum tensor of the gravitational field is given by the pseudotensor of Landau-Lifshitz’s classic textbook. Here, we demonstrate that this result also holds when the self-interaction of a scalar field is taken into account. That is, our two-loop-order calculation suggests that, in an effective field theory of metric and scalar fields, one arrives at a consistent theory with massless gravitons if the cosmological constant is fixed from the condition of vanishing vacuum energy. Vice versa, imposing the consistency condition in Minkowskian background leads to a vanishing vacuum energy.

It has been known that warped-product spacetimes such as spherically symmetric ones admit the Kodama vector. This vector provides a locally conserved current made by contraction of the Einstein tensor, even though there is no Killing vector. In addition, a quasilocal mass, Birkhoff’s theorem, and various properties are closely related to the Kodama vector. Recently, it is shown that the notion of the Kodama vector can be extended to three-dimensional axisymmetric spacetimes even if the spacetimes are not warped product. This implies that warped product may not be a necessary condition for a spacetime to admit the Kodama vector. We show properties of the Kodama vector originate from the conformal Killing-Yano 2-form. In particular, the well-known spacetimes that admit the Kodama vector have a closed conformal Killing-Yano 2-form. Furthermore, we show the Kodama vector provides local conserved currents for each order of the Lovelock tensor as well as the Einstein tensor.

Singularity theorems demonstrate the inevitable breakdown of the concept of continuous, classical spacetime under highly general conditions. Quantum gravity is expected to intervene to avoid singularities, and models so far hint toward several regularized geometries, in which limited spacetime regions requiring full quantum gravitational description can be safely covered by an extension of some suitable spacetime geometry. Motivated by these premises, in recent years, a systematic, quantum gravity agnostic study has been carried out to catalog all the conceivable nonsingular, continuous, and globally hyperbolic geometries arising from evading Penrose’s focusing theorem in gravitational collapse. In this study, we extend this inquiry by systematically examining all potential nonsingular, continuous, and globally hyperbolic extensions into the past of Friedmann-Lemaître-Robertson-Walker metrics. As in the black-hole case, our investigation reveals a remarkably limited set of alternative scenarios. The stringent requisites of homogeneity and isotropy drastically restrict the viable singularity-free geometries to merely three discernible nonsingular cosmological spacetimes: a bouncing universe (where the scale factor reaches a minimum in the past before reexpanding), an emergent universe (where the scale factor reaches and maintains a constant value in the past), and an asymptotically emergent universe (where the scale factor diminishes continually, asymptotically approaching a constant value in the past). We also discuss the implications of these findings for the initial conditions of our Universe, and the arrow of time.

We study lensing of gravitational waves by a black hole in the deep wave optics regime, i.e., when the wavelength is much larger than the black hole Schwarzschild radius. We apply it to triple systems, with a binary of stellar-mass objects in the inspiraling phase orbiting around a central massive black hole. We describe the full polarization structure of the wave and derive predictions for the polarization modes of the scattered wave measured by the observer. We show that lensing in the wave optics regime is not helicity preserving, as opposed to lensing in the geometric optics regime. The amplitude of the total wave is modulated due to interference between the directly transmitted and lensed components. The relative amplitude of the modulation is fixed by the lensing geometry and can reach unity in the most favorable settings. This indicates that wave optics lensing is potentially detectable by the Laser Interferometer Space Antenna for sufficiently high SNR systems. Our findings show that in the wave optics regime it is necessary to go beyond the usual lensing description where the amplification factor is assumed to be the same for both helicity modes. While motivated by GW190521 and the active galactic nuclei formation scenario, our results apply more broadly to stellar-mass binaries orbiting a third body described as a Schwarzschild black hole, with a period comparable to the gravitational wave observation time.

We identify axion miniclusters collapsing in the radiation-dominated era and follow them to redshift $z=99$ with $N$-body simulations. We find that the majority of the densest miniclusters end up in the center of larger minicluster halos at late times. Soon after their formation, the miniclusters exhibit Navarro-Frenk-White (NFW) profiles but they subsequently develop a steeper inner slope approaching $\rho \sim r^{-2}$ on small scales. Using the so far most highly resolved axion structure formation simulation with ${2048}^3$ particles we examine the structure of previously studied minicluster halos. While the density profiles of their subhalos are NFW-like we confirm that a modified NFW profile with a steeper inner slope provides a better description for minicluster halos with masses above $\sim {10}^{-12}{M}_{\odot }$. We show that miniclusters with a higher central density might be in contrast to pure NFW halos dense enough to induce gravitational microlensing. Likewise, more compact minicluster halos will have immediate implications for direct and indirect axion detection.

There has recently been some considerable interest expressed in a highly speculative model of black-hole evolution—allegedly by a postulated direct coupling between black holes and cosmological expansion independent of accretion or mergers. We wish to make several cautionary comments in this regard—at least three exact solutions corresponding to black holes embedded in a Friedmann-Lemaître-Robertson-Walker background are known (Kottler, McVittie, Kerr–de Sitter), and they show no hint of this claimed effect, thereby implying that this claimed effect (if it exists at all) is certainly nowhere near ubiquitous.

We investigate how vector-isoscalar and vector-isovector interactions can be determined within the density regime of neutron stars (NSs), while fulfilling nuclear and astrophysics constrains. We make use of the chiral mean field model, a SU(3) nonlinear realization of the sigma model within the mean-field approximation, for the first time within a Bayesian analysis framework. We show that neutron-matter chiral effective field theory constraints at low density are only satisfied if the vector-isovector mixed interaction term is included, e.g., a ${\omega }^2{\rho }^2$ term. We also show the behavior of the model with respect to the conformal limit. We demonstrate that the chiral mean field model is able to predict a value for the parameter $d_c$ related to the trace anomaly and its derivative takes values below 0.2 above four times saturation density within a hadronic version of the model that does not include hyperons or a phase transition to deconfined matter. We compare these effects with results from other (nonchiral) relativistic mean field models to assess how different approaches to incorporating the same physical constraints affect predictions of NS properties and dense matter uations of state. We also include data from the gravitation wave event GW230529 detected by the LIGO-Virgo-KAGRA collaboration and the most recent radius measurement of PSR J0437-4715 from the NASA NICER mission. Our analysis reveals that this new NICER measurement leads to an average reduction of approximately $\sim 0.1\mathrm{km}$ radius in the posterior of the NS mass-radius relationship.

We demonstrate a novel mechanism for producing dark compact objects and black holes through a dark sector, where all the dark matter can be dissipative. Heavy dark sector particles with masses above ${10}^4\mathrm{GeV}$ can come to dominate the Universe and yield an early matter-dominated era before big bang nucleosynthesis (BBN). Density perturbations in this epoch can grow and collapse into tiny dark matter halos, which cool via self-interactions. The typical halo size is set by the Hubble length once perturbations begin growing, offering a straightforward prediction of the halo size and evolution depending on one’s choice of dark matter model. Once these primordial halos have formed, a thermal phase transition can then shift the Universe back into radiation domination and standard cosmology. These halos can continue to collapse after BBN, resulting in the late-time formation of fragmented dark compact objects and sub-solar-mass primordial black holes. We find that these compact objects can constitute a sizable fraction of all of dark matter. The resulting fragments can have masses between ${10}^{20}$ and ${10}^{32}\mathrm{g}$, with radii ranging from ${10}^{-2}$ to ${10}^5\mathrm{m}$, while the black holes can have masses between ${10}^8$ and ${10}^{34}\mathrm{g}$. Furthermore, a unique feature of this model is the late-time formation of black holes which can evaporate today. We compare where these objects lie with respect to current primordial black hole and massive (astrophysical) compact halo object constraints.

The potential role of a cosmic vacuum dark component in the properties of neutron stars is investigated. It is assumed that the static, spherically symmetric distribution of matter within neutron stars is supported by two distinct components: ordinary matter and a vacuum fluid. For normal matter we use a set of state-of-the-art nuclear matter equations of state, each grounded in nuclear physics experiments. The vacuum energy component is inhomogeneously distributed within the star and obeys the standard equation of state ($p_v=-{\epsilon }_v$). This is characterized by an energy density fraction $y={\epsilon }_m/({\epsilon }_m+{\epsilon }_v)$, which we model as either a constant or radius-dependent. Our findings reveal that the inclusion of vacuum energy significantly affects the mass-radius relationships in neutron stars, influencing both the maximum achievable masses and the qualitative form of these relationships. Some constraints from current multimessenger observational data limiting the amount of vacuum energy within neutron stars are also discussed.

Neutrinos are known to undergo flavor conversion among their three flavors. In the theoretical modeling of core-collapse supernova, there has been a great deal of attention to recent discoveries of a new type of neutrino flavor conversions, namely collisional flavor instability (CFI), in which the instability is induced by the flavor-dependent decoherence due to the disparity of neutrino-matter interactions among flavors. In this paper, we study how the appearance of on-shell muons and associated neutrino-matter interactions can impact CFIs based on linear stability analysis of flavor conversions. Some striking results emerge from the present study. First, we analytically show that breaking beta and pair equilibrium is a necessary condition to trigger CFIs. This also indicates that CFIs with on-shell muons could appear in $e\tau$ and $\mu \tau$ neutrino mixing sectors in very high-density region ($\gtrsim {10}^{13}\mathrm{g}/{\mathrm{cm}}^3$), exhibiting a possibility of large impacts of CFIs on core-collapse supernova. Second, resonancelike CFIs, having a much higher growth rate than normal CFIs, can be triggered by muons. The resonance point of CFIs is different between $e\tau$ and $\mu \tau$ sectors; the former (latter) occurs at ${\mu }_{e(\mu )}={\mu }_n-{\mu }_p$, where ${\mu }_i$ denotes the chemical potential of $i$ constitute ($n$ and $p$ represent neutrons and protons, respectively). Our result suggests that the nonlinear evolution of CFI with on-shell muons would induce flavor conversions with the complex interplay among all three different neutrino-mixing sectors.

We revisit the contribution to the strong $CP$ parameter $\overline{\theta }$ from leptonic $CP$ violation at one-loop level in the minimal left-right symmetric model in the case of generalized parity as the left-right symmetry. The Hermitian neutrino Dirac mass matrix $M_D$ can be calculated using the light and heavy neutrino masses and mixings. We propose a parametrization of the right-handed neutrino mixing matrix $V_R$ and construct the heavy neutrino mass that maintains the Hermiticity of $M_D$. We further apply it to evaluate the one-loop $\overline{\theta }$, denoted as ${\overline{\theta }}_{\mathrm{loop}}$, as a function of the sterile neutrino masses for explicit examples of $V_R$. By requiring the magnitude of ${\overline{\theta }}_{\mathrm{loop}}\lesssim {10}^{-10}$, we derive the upper limits on the sterile neutrino masses, which are within reach of direct searches at the Large Hadron Collider and neutrinoless double beta decay experiments. Furthermore, our parametrization is pertinent for other phenomenological investigations.

$T_{cc}^{+}$ is an isoscalar 4-quark state with mass lying barely below the $D^{*+}{D}^0$ threshold, and several times further below the $D^{*0}{D}^{+}$ threshold. It allows both dimeson molecular and elementary diquark-antidiquark $(cc)(\overline{u}\overline{d})$ substructures. The diabatic generalization of the adiabatic approximation within the Born-Oppenheimer formalism rigorously incorporates the mixing of such elementary eigenstates with states corresponding to two-particle thresholds. We examine the separate influence of the two $D^{*}D$ isospin channels and find that the influence of $D^{*+}{D}^0$ is larger than that of $D^{*0}{D}^{+}$ but not overwhelmingly so, and that $T_{cc}^{+}$ contains an $O(10\%)$ $(cc)(\overline{u}\overline{d})$ component. We then explore the variation of these results if the isospin breaking between the dimeson thresholds is varied, and also the sensitivity of our results to variation of the mixing-potential parameters.

Using $(27.12\pm 0.14)\times {10}^8$ $\psi (3686)$ events collected with the BESIII detector, we present the first observation of the decays ${\chi }_{cJ}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\omega$, where $J=0$, 1, 2, with statistical significances of $11.7\sigma$, $11.2\sigma$, and $11.8\sigma$. The branching fractions of these decays are determined to be $\mathcal{B}({\chi }_{c0}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\omega )=(2.37\pm 0.22\pm 0.25)\times {10}^{-4}$, $\mathcal{B}({\chi }_{c1}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\omega )=(1.01\pm 0.10\pm 0.11)\times {10}^{-4}$, and $\mathcal{B}({\chi }_{c2}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\omega )=(1.40\pm 0.13\pm 0.17)\times {10}^{-4}$, where the first uncertainties are statistical and the second are systematic. We observe no clear intermediate structures.

We search for excited charmed baryons in the ${\mathrm{\Lambda }}_c^{+}\eta$ system using a data sample corresponding to an integrated luminosity of $980{\mathrm{fb}}^{-1}$. The data were collected by the Belle detector at the KEKB $e^{+}{e}^{-}$ asymmetric-energy collider. No significant signals are found in the ${\mathrm{\Lambda }}_c^{+}\eta$ mass spectrum, including the known ${\mathrm{\Lambda }}_c(2880{)}^{+}$ and ${\mathrm{\Lambda }}_c(2940{)}^{+}$. Clear ${\mathrm{\Lambda }}_c(2880{)}^{+}$ and ${\mathrm{\Lambda }}_c(2940{)}^{+}$ signals are observed in the $p{D}^0$ mass spectrum. We set upper limits at 90% credibility level on ratios of branching fractions of ${\mathrm{\Lambda }}_c(2880{)}^{+}$ and ${\mathrm{\Lambda }}_c(2940{)}^{+}$ decaying to ${\mathrm{\Lambda }}_c^{+}\eta$ relative to ${\mathrm{\Sigma }}_c(2455)\pi$ of $<0.13$ for the ${\mathrm{\Lambda }}_c(2880{)}^{+}$ and $<1.11$ for the ${\mathrm{\Lambda }}_c(2940{)}^{+}$. We measure ratios of branching fractions of ${\mathrm{\Lambda }}_c(2880{)}^{+}$ and ${\mathrm{\Lambda }}_c(2940{)}^{+}$ decaying to $p{D}^0$ relative to ${\mathrm{\Sigma }}_c(2455)\pi$ of $0.75\pm 0.03(\mathrm{stat})\pm 0.07(\mathrm{syst})$ for the ${\mathrm{\Lambda }}_c(2880{)}^{+}$ and $3.59\pm 0.21(\mathrm{stat})\pm 0.56(\mathrm{syst})$ for the ${\mathrm{\Lambda }}_c(2940{)}^{+}$.

We investigate a long-overlooked $CP$ violation effect—the double-mixing $CP$ asymmetry—in a type of cascade decay that involves at least two mixing neutral mesons in the decay chain. It is induced by the interference between different oscillation paths of the neutral mesons in the decay process. The double-mixing $CP$ asymmetry is of critical importance for phenomenology, providing opportunities for clean determination of Cabibbo-Kobayashi-Maskawa phase angles free of uncertainties induced by the strong dynamics. To illustrate this point, we perform a phenomenological analysis on two examples: $B_s^0\to {\rho }^{0}K\to {\rho }^0({\pi }^{-}{\ell }^{+}{\nu }_{\ell })$ and $B^0\to D^{0}K\to D^0({\pi }^{+}{\ell }^{-}{\overline{\nu }}_{\ell })$. Our results demonstrate that the double-mixing $CP$ asymmetry can be numerically significant in the absence of strong phases, as shown by the former example. Additionally, the latter example showcases a direct extraction of weak and strong phases from data, without the need for theoretical inputs.

We report the result of a search for the rare decay $B^0\to \gamma \gamma$ using a combined dataset of $753\times {10}^{6}B\overline{B}$ pairs collected by the Belle experiment and $387\times {10}^{6}B\overline{B}$ pairs collected by the Belle II experiment from decays of the $\mathrm{\Upsilon }(4\mathrm{S})$ resonance produced in $e^{+}{e}^{-}$ collisions. A simultaneous fit to the Belle and Belle II data sets yields ${11.0}_{-5.5}^{+6.5}$ signal events, corresponding to a $2.5\sigma$ significance. We determine the branching fraction $\mathcal{B}(B^0\to \gamma \gamma )=({3.7}_{-1.8}^{+2.2}(\text{stat})\pm 0.5(\text{syst}))\times {10}^{-8}$ and set a 90% credibility level upper limit of $\mathcal{B}(B^0\to \gamma \gamma )<6.4\times {10}^{-8}$.

We examined the quantum properties of scalar-tensor gravity with a coupling to the Gauss-Bonnet term in the low-energy limit, exploring both linear and quadratic couplings. We calculated the leading-order corrections to the nonrelativistic one-body gravitational potential and the metric by studying the gravitational field of a pointlike scalar particle. We studied lightlike scattering and compared it with the classical theory. We found that the nonminimal coupling does not contribute to the small-angle scattering for the quadratic coupling but does in the case of linear coupling. The results provide an opportunity to constrain the linear nonminimal coupling to the Gauss-Bonnet term with forthcoming observational data.

Near horizons, quantum fields of low spin exhibit densities of states that behave asymptotically like $1+1$ dimensional conformal field theories. In effective field theory, imposing some short-distance cutoff, one can compute thermodynamic quantities associated with the horizon, and the leading cutoff sensitivity of the heat capacity is found to equal to the leading cutoff sensitivity of the entropy. One can also compute contributions to the thermodynamic quantities from the gravitational path integral. For the cosmological horizon of the static patch of de Sitter space, a natural conjecture for the relevant heat capacity is shown to equal the Bekenstein-Hawking entropy. These observations allow us to extend the well-known notion of the generalized entropy to a generalized heat capacity for the static patch of de Sitter (dS). The finiteness of the entropy and the nonvanishing of the generalized heat capacity suggest it is useful to think about dS as a state in a finite dimensional quantum gravity model that is not maximally uncertain.

We apply an algebraic double copy construction of gravity from gauge theory to three-dimensional (3D) Chern-Simons theory. The kinematic algebra $\mathcal{K}$ is the 3D de Rham complex of forms equipped, for a choice of metric, with a graded Lie algebra that is equivalent to the Schouten-Nijenhuis bracket on polyvector fields. The double copied gravity is defined on a subspace of $\mathcal{K}\otimes \overline{\mathcal{K}}$ and yields a topological double field theory for a generalized metric perturbation and two 2-forms. This local and gauge invariant theory is non-Lagrangian but can be rendered Lagrangian by abandoning locality. Upon fixing a gauge this reduces to the double copy of Chern-Simons theory previously proposed by Ben-Shahar and Johansson. Furthermore, using complex coordinates in ${\mathbb{C}}^3$ this theory is related to six-dimensional (6D) Kodaira-Spencer gravity in that truncating the two 2-forms and one equation yields the Kodaira-Spencer equations on a 3D real slice of ${\mathbb{C}}^3$. The full 6D Kodaira-Spencer theory can instead be obtained as a consistent truncation of a chiral double copy.