Given two otherwise decoupled $D$-dimensional CFTs which possess a common (finite) symmetry subcategory, one can consider entangled boundary states of their ($D+1$)-dimensional symmetry topological field theories (SymTFTs). This roughly corresponds to performing a gauging of the tensor product of two CFTs, and we call this phenomena “SymTFT entanglement” (or “S entanglement” for short). In the case when these CFTs have semiclassical holographic duals, the S entanglement relates the bulk gauge charges between two otherwise disconnected AdS spacetimes as we highlight in several top-down examples. We show that taking partial traces of such S-entangled states leads to a streamlined approach to preparing ensemble-averaged CFTs in string theory. This ensemble averaging coincides with that generated by $\alpha$ states in the baby universe Hilbert space, and we propose a symmetry-enriched generalization of this Hilbert space via generalized global symmetries. We quantify how this symmetry-governed averaging violates holographic factorization and leads to the emergence of bulk global symmetries. We also consider the eternal (two-sided) AdS black hole geometries, where our SymTFT entanglement considerations imply that there exist refinements of the usual theromofield double state preparation of the system. We show that one may prepare the system in such a way that the total CFT data does not factorize into left and right copies. As anticipated by Marolf and Wall [Classical Quantum Gravity 30, 025001 (2013)], we highlight that such considerations are necessary to define the gauge charges of eternal black holes and, in certain cases, can imply that there exist extended bulk objects stretching across the wormhole which cannot be expressed in terms of a product of left and right CFT operators.

We demonstrate that $n$-way junctions in three-dimensional gravity correspond to coupled $n-1$ strings each satisfying the Nambu-Goto equation in the smoothened background and with sources consisting of Monge-Ampère like terms which couple the strings. For $n\ge 3$, these $n-1$ degrees of freedom survive the tensionless limit implying that matterlike behavior can arise out of pure gravity. We interpret these stringy degrees of freedom of gravitational junctions holographically in terms of wave packets, which collectively undergo perfect reflection at the multi-interface in the dual conformal field theory.

The fuzzy onion model formed by connecting a set of concentric fuzzy spheres of increasing radius is motivated by studies of quantum space but can also be used to study standard physics. The main feature of the model is that functions in three-dimensional space—like scalar fields or wave functions—are expressed in terms of Hermitian matrices of a certain structure. Relevant equations are then matrix equations, and some problems, such as searching for the energy spectrum for fixed quantum numbers $(l,m)$, can be expressed as an eigenvalue problem. We show how this simple approach can reproduce the results of other studies analyzing the hydrogen atom in a spherical cavity. We also test the effect of the short-distance quantum structure of the space on these solutions—not looking for the phenomenological consequences, as the scale of quantum space is many orders below the order of the Bohr radius, but to understand the effect of quantum space in general. We observe a set of solutions without a classical counterpart which have been suggested also in a former theoretical study.

Why (and how) the Universe was born is one of the ultimate questions in physics. Another big puzzle is about the arrow of time: Why is there only one direction of time? Are these two issues related? One way to solve both puzzles at one stroke is to posit that our Universe was pair-created with a twin, whose time arrow is opposite to ours. If so, then the twins must naturally be quantum entangled. In Euclidean quantum gravity, this implies the existence of a Euclidean wormhole bridging the twin universes. Each universe is then in a mixed state, and the mutual entanglement shall leave signatures in the cosmic microwave background (CMB) power spectrum. Invoking the Klebanov-Susskind-Banks wormhole as a toy model for the sake of tractability, we show that the entanglement selects a novel and unique nonthermal global vacuum for the total inflaton perturbations in both universes. This is equivalent to imposing a simple harmonic oscillator boundary condition on the Euclidean wave function of the total perturbations, and it turns out that the entanglement enhances the CMB power spectrum for long-wavelength modes. Such a birthmark renders our notion refutable.

Recent advances in holography and quantum gravity have shown that conformal field theories (CFTs) with classical gravity duals can implement nonlocal quantum computation protocols that appear local from the bulk perspective. We examine the extent to which current prescriptions for holographic complexity support this claim, focusing on the $\mathrm{complexity}=\text{volume}$ (CV) proposal. The reformulation of CV in terms of Lorentzian threads suggests that bulk computations are performed with local gates. However, we find that the original formalism is insufficient when it comes to analyzing the complexity of subsystems and their inequalities. Specifically, standard Lorentzian threads cannot account for the negativity of mutual complexity and its higher-partite generalizations. To address this deficiency, we modify the Lorentzian threads program by introducing multiple flavors of threads. Our analysis reveals that an optimal solution for this new program implies the existence of additional types of gates that enable nonlocal computations in the dual CFT. We give a tentative interpretation of the multiflavor program in terms of Lorentzian hyperthreads, in analogy with the Riemannian case.

We show that the chiral algebra bootstrap, which computes form factors of twistorial theories, can help determine two-loop amplitudes in massless QCD. We give an $n$-gluon result for a previously unknown partial amplitude of the two-loop all-plus-helicity QCD amplitude by utilizing supersymmetry Ward identities and known chiral algebra bootstrap results. We then show that the full-color two-loop $n$-gluon amplitude of QCD with $n_f$ quark flavors can be obtained from certain two-loop form factors of twistorial theories and one-loop and tree-level amplitudes. Chiral algebra bootstrap results exist for these form factors when all gluons have positive helicities. Hence, the bootstrap simplifies the computation of these two-loop amplitudes by one loop level.

We compute the parity-odd part of the Weyl anomaly for chiral fermions in a background gravitational field. We start from a manifestly real form of the Lagrangian (that is, not only real up to a total derivative), and we regularize it by means of Pauli-Villars fermions. All parity-odd terms in the anomaly cancel in the integrand, so that the result of the anomaly is necessarily parity even.

We study the number of degrees of freedom (DOFs) in quadratic scalar-nonmetricity (QSN) theory, whose Lagrangian is the linear combination of five quadratic nonmetricity invariants with coefficients depending on a dynamical scalar field. Working in the coincident gauge, we perform the Arnowitt-Deser-Misner decomposition and classify QSN models into 13 cases according to the numbers of their primary constraints. For cases that are physically viable in the sense that both a consistent cosmological background and tensor gravitational waves exist, we count the number of DOFs based on two approaches. First, we investigate the linear cosmological perturbations around a Friedmann-Lemaître-Robertson-Walker background. Then we perform a Dirac-Bergmann Hamiltonian constraint analysis to count the number of DOFs at the nonperturbative level. We focus on three representative cases. In case II, both the perturbative and nonperturbative approaches yield the same result, which indicates that the theory propagates 10 degrees of freedom. In contrast, in cases V and VI, the Hamiltonian analysis yields 8 degrees of freedom, while only 6 and 5 modes are visible at linear order in perturbations, respectively. This indicates that additional modes are strongly coupled on cosmological backgrounds.

The Euclidean action provides a bridge between gravitational thermodynamics and the partition function. In this work, we further investigate the gravitational partition function under a fixed-volume constraint, generalizing the fixed-volume on-shell geometry in the massless case. Moving beyond this massless configuration, we construct solutions with nonvanishing mass functions, which give rise to a new class of volume-constrained Euclidean geometries (VCEGs). These geometries possess both a boundary and a horizon. However, closer inspection indicates that the boundary is not intrinsic, but rather artificially introduced and can be extended, leading to the extended volume-constrained Euclidean geometries (EVCEGs). The EVCEGs contain two horizons, each generically associated with a conical singularity. Their Euclidean action is given by one quarter of the sum of the areas of the two horizons. In general, the conical singularities at the two horizons cannot be simultaneously eliminated, except at a critical mass $m=m^{*}$, which defines the critical EVCEG. Configurations with unavoidable conical singularities are naturally interpreted as constrained gravitational instantons. An analysis of their contributions to the partition function, together with their topological properties, reveals a close analogy between the EVCEGs and the Euclidean Schwarzschild-de Sitter static patch. This suggests that the volume constraint effectively plays a role analogous to that of a cosmological constant in semiclassical quantum gravity.

The theory of force-free electrodynamics (FFE) provides a robust framework for modeling the magnetospheres of compact objects, where the electromagnetic field’s energy density dominates the surrounding plasma. Central to this theory is the existence of two-dimensional integral submanifolds, or field sheets, which foliate the spacetime. While it is established that every null force-free field possesses an associated 2-D null geodesic foliation [see Govind Menon, Classical Quantum Gravity 38, 045011 (2021) for details], the converse—identifying which null geodesic congruences can support a force-free solution—remains a nontrivial computational challenge. In this paper, we extend the foliation-based approach to null FFE by addressing two primary obstacles to the existence of a solution: the equipartition of null mean curvature and the involutivity of the field sheet distribution. We prove a general existence theorem demonstrating that for any given null geodesic congruence, there always exists a local rotation of a 2-D basis transverse to the geodesic congruence that satisfies the equipartition condition. Furthermore, we establish that a shear-free null geodesic congruence is sufficient to guarantee the existence of an arbitrary function of three variables such that any choice of such a function will generate a null field sheet foliation. Additionally, each unique foliation will be associated with a null force-free field that further contains an arbitrary function of two variables. These results are formally linked to the vanishing of the shear tensor, providing a coordinate-independent geometric criterion for the existence of null FFE solutions. We illustrate these theorems with explicit examples in Schwarzschild and Kerr geometries and present new, nontrivial exact null solutions in flat spacetime and for the C-metric.

We present a new approach to measuring cosmic shear: the one-component kinematic lensing (KL) method. This technique provides a simplified implementation of KL that reduces shape noise in weak lensing (WL) by combining kinematic information with imaging data, while requiring less observational effort than the full two-component KL. We perform simulated likelihood analyses to assess the performance of the one-component KL and demonstrate its applicability to future radio surveys. Our forecasts indicate that, for radio surveys, the one-component KL is not yet competitive with traditional WL due to the shallow redshift distribution of Hi-selected galaxies. However, when applying this method to deeper spectroscopic surveys with stronger emission lines, the one-component KL approach could surpass WL in constraining power, offering a promising and efficient pathway for future shear analyses.

We study a minimal type-I seesaw framework in which a first-order phase transition, driven by a singlet scalar $\varphi$, produces right-handed neutrinos (RHNs) through bubble collisions, realizing a cosmic-scale collider that probes ultrahigh energy scales. The resulting inhomogeneous RHN distribution sources a novel low-frequency gravitational-wave (GW) signal in addition to the standard bubble-collision contribution. A stable lightest RHN can account for the observed dark-matter (DM) relic abundance for masses as low as $M_1\equiv m_{\mathrm{DM}}\gtrsim {10}^6\mathrm{GeV}$, with the associated novel GW signal accessible in the Laser Interferometer Space Antenna, Einstein Telescope (ET), and upcoming LIGO-Virgo-KAGRA (LVK) detectors. If the RHNs are unstable, their $CP$-violating decays generate the baryon asymmetry via leptogenesis for $M_1\gtrsim {10}^{11}\mathrm{GeV}$ and phase transition temperatures $T_{*}\gtrsim {10}^6\mathrm{GeV}$, yielding the novel GW signatures within the reach of ET, Big Bang Observer (BBO), and upcoming LVK detectors. Part of the parameter space is already constrained by the LVK $\mathcal{O}(3)$ data. If RHN decays populate a dark sector fermion $\chi$ with mass $m_{\chi }\in [{10}^{-4},{10}^4]\mathrm{GeV}$, successful cogenesis of baryons and asymmetric dark matter is achieved for $T_{*}\gtrsim {10}^7\mathrm{GeV}$ and $M_1\gtrsim {10}^9\mathrm{GeV}$, naturally explaining ${\mathrm{\Omega }}_{\mathrm{DM}}\simeq 5{\mathrm{\Omega }}_{\mathrm{B}}$. The corresponding GW signals are testable with Laser Interferometer Space Antenna, ET, and BBO. Finally, we analyze a UV-complete multi-Majoron model based on a global $U(1{)}_N\times U(1{)}_{\mathrm{B}-\mathrm{L}}$ extension of Standard Model, motivated from the hierarchy of lepton masses, in which a distinctive GW signature associated with a cosmic Majoron collider arises from scalar production during $U(1{)}_N$ symmetry breaking, detectable by BBO, ET, and upcoming LVK. Successful leptogenesis is realized for the heaviest RHN mass $M_3\sim {10}^{10}\mathrm{GeV}$ and a $U(1{)}_N$ breaking vacuum expectation value $v_2\sim \mathcal{O}(\mathrm{TeV})$ that sets the seesaw scale.

The multimessenger detection of the binary neutron star (NS) merger GW170817 has revolutionized the field of gravitational wave (GW) astronomy. However, several important questions remain to be answered. One of these is the nature of the compact remnant leftover by GW170817 (short- or long-lived NS versus black hole). A key goal going forward is to understand the diversity of NS-NS merger remnants, and how such diversity maps onto their viability as gamma-ray burst (GRB) central engines. Here, we present a study aimed at assessing the sensitivity of triggered searches for intermediate-duration, postmerger GWs powered by long-lived GRB remnants using networks of current and future ground-based GW detectors and the cross-orrelation algorithm (CoCoA). We develop a python-based framework to efficiently estimate CoCoA distance horizons for a broad range of postmerger secular bar-mode waveforms and for different GW detector networks. This framework can be used to identify the most promising regions of parameter space in which to concentrate search efforts, helping to design future search strategies to optimally balance search sensitivity and related parameter space gridding schema against computational cost.

Building on the first-ever application of neural networks in transverse momentum distribution (TMD) phenomenology—“Extraction of the Sivers function with deep neural networks”—we now present a momentum-space, physics-informed deep-learning framework for the direct extraction of unpolarized transverse-momentum-dependent parton distribution functions (TMDs) from fixed-target Drell-Yan data (E288, E605). Rather than transforming to impact-parameter space, we remain in $k_{\perp }$ and embed a normalized integrand $s(x,k_{\perp };Q)$ whose autoconvolution produces the observed $q_T$ spectra. We introduce two phenomenological objects in this data-driven approach: the transverse structure kernel $S(q_T,x_1,x_2;Q)$ and the intrinsic-transverse-momentum profile $s(x,k_{\perp };Q)$. The extraction proceeds in two steps. Stage I learns the structure kernel $S(q_T,x_1,x_2;Q_M)$ by regressing the cross section with known kinematic prefactors and charge-weighted parton distribution function (PDF) combinations factored out; experimental and PDF uncertainties are propagated with Monte Carlo replicas. Stage II reconstructs $s(x,k_{\perp };Q)$ with an end-to-end differentiable $k_{\perp }$ quadrature layer. Applied to Fermilab cross-section data from experiments E288 and E605, the method reproduces the measured $q_T$ spectra across the $Q_M$ bins and yields $x$- and $Q$-dependent TMDs that broaden with $Q$, with uncertainty bands that consistently propagate experimental, PDF, algorithmic, and methodological components. The approach is minimally biased (no factorized Ansätze and no $b_T$ transform) and provides a transferable template for polarized TMDs and related quantum chromodynamics inverse problems.

We present a perturbative closed-time-path (in-in) formulation of an optomechanical system in which a quantum field interacts with a moving mirror via radiation-pressure. We derive the effective action governing the dynamics of the moving mirror, incorporating the full backreaction of the field. These effects are encoded in fluctuation and dissipation kernels, that we show satisfy fluctuation-dissipation relations, and whose spectral structure reveals a direct connection with the underlying physical mechanism responsible for the backreaction, that is particle creation by the dynamical Casimir effect. By deriving the semiclassical equations of motion for the moving mirror, and computing the energy radiated into the field using the in-out formalism of quantum field theory, we verify the energy balance between the mechanical energy dissipated by the optical backreaction forces acting on the mirror and the energy carried by the particles created in the field.

Recent results from the Large Hadron Collider have demonstrated quantum entanglement of top quark–antiquark pairs using the spin degrees of freedom. Based on the doubly differential measurement of the spin density matrix of the top quark and antiquark performed by the CMS collaboration in the helicity and beam bases, we evaluate a set of quantum observables, including discord, steerability, Bell correlation, and magic. These observables allow for a quantitative characterization of the quantum correlations present in a top quark–antiquark system, thus enabling an interpretation of collider data in terms of quantum states and their properties. Discord is observed to be greater than zero with a significance of more than 5 standard deviations ($\sigma$) in several regions of phase space, some of which correspond to separable quantum states. Evidence for steerability is established for the first time in a high-energy system, with a significance of more than $3\sigma$. No Bell correlation is observed within the currently probed phase space, in agreement with the theoretical prediction. These results experimentally corroborate the hierarchy of quantum correlations in top quarks with discord being the most basic form of quantum correlation, followed by entanglement, steerability, and Bell correlation. The significance of nonzero magic, which is a complementary observable to the quantum correlation hierarchy, is found to exceed $5\sigma$ in several regions of phase space.

In this study, we explore temperature-dependent $CPT$ violation during big bang nucleosynthesis (BBN) through electron-positron mass asymmetries parametrized by $b_0(T)=\alpha T^2$. The $T^2$ scaling naturally evades stringent laboratory bounds at zero temperature while allowing for significant $CPT$ violation at MeV scales in the early Universe [S. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024)]. Using a modified version of the BBN code PRyMordial with dynamically-solved chemical potentials and appropriate finite-mass corrections, we constrain electron-positron mass differences from observed abundances of helium-4, deuterium, and $N_{\mathrm{eff}}$. We find that $\alpha$ must be greater than or approximately equal to ${10}^{-6}{\mathrm{GeV}}^{-1}$ for keV-scale mass differences at BBN. All three observables show no simultaneous $1\sigma$ overlap, though pairwise combinations allow for constrained regions of parameter space. We present two toy models demonstrating how $b_0(T)\propto T^2$ arises from field-theoretic mechanisms, including temperature-driven phase transitions. These results provide the most stringent constraints on early-Universe $CPT$ violation in this regime, probing parameter space inaccessible to laboratory experiments.

Accurate signal predictions are essential for interpreting and optimizing fixed-target searches for new physics. Even in minimal models such as the dark photon ($A^{\prime }$) or millicharged particles (mCPs), theoretical uncertainties in hadronic production can be substantial. We introduce a data-driven framework that predicts both the rate and kinematic distributions of $A^{\prime }$ and mCP production directly from measured dilepton events, without relying on specific theoretical production models. This method uses the close correspondence between amplitudes for emission of $A^{\prime }$ or mCPs, and for off-shell Standard Model photon production, the latter being experimentally measurable in full differential form. We demonstrate that normalizing flow models can learn these distributions from data and serve as a fast, realistic Monte Carlo generator for dark sector signal simulations.

We study methods for efficient preparation of approximate ground states of $SU(3)$ lattice gauge theory on quantum hardware. Working in a variant of the electric basis, we introduce a refinement of the irrep truncation based on the energy density of site singlets, which provides a finer gradation of simulation complexity. Using strong-coupling perturbation theory as a guide, we develop simple ansatz circuits for ground state preparation and test them via classical simulation on small lattices, including the $2\times 2$ plaquette lattice in $d=2$ and the cube in $d=3$. We contrast state fidelities and resource requirements of variational methods against adiabatic state preparation and introduce a method that hybridizes the two approaches. Finally, we report on the public release of ymcirc—a package of tools for building $SU(3)$ circuits and processing measurements—and pyclebsch, a package for efficiently computing $SU(N)$ Clebsch–Gordan coefficients.

The role of spin degrees of freedom in the quark-gluon plasma (QGP) has attracted significant interest in recent years. Spin hydrodynamics extends conventional hydrodynamics by incorporating spin via the spin tensor. In the mean-field limit of the Nambu–Jona-Lasinio (NJL) model under rigid rotation, spin degrees of freedom manifest naturally as axial-vector, or spin, condensate. We investigate the interplay between chiral and spin condensates in this framework. While rotation typically suppresses the formation of a chiral condensate, the presence of a spin condensate may counteract this effect, enhancing the chiral condensate. Moreover, it can alter the nature of the chiral transition from second to first order.