We show that the Lagrangian of a Nambu-Goto $p$-brane satisfies the identity ${\mathcal{L}}_{[p]}=T_{[p]}/(p+1)$, with $T_{[p]}$ denoting the trace of the corresponding energy-momentum tensor, independently of the properties of the gravitational field. While for $p=0$ this reduces to the standard ${\mathcal{L}}_{[0]}=T_{[0]}$ relation, which determines the on-shell Lagrangian of point particles and their fluids, more generally it depends explicitly on the $p$-brane dimensionality. We explore the implications of this Lagrangian identity for the dynamics of non-self-intersecting cosmic string loops in a homogeneous and isotropic universe within nonminimally coupled scalar-tensor gravity, showing that, unlike in general relativity, their rest mass can evolve in response to the cosmological evolution of the background spacetime, regardless of their small size or tension. We further generalize this analysis to closed $p$-branes in ($N+1$)-dimensional Friedmann-Lemaître-Robertson-Walker spacetimes, showing that the evolution of the rest mass depends explicitly on the dimensionality of the brane, and therefore that the cosmological evolution of particlelike objects in theories of gravity with nonminimal matter couplings is sensitive to their internal structure.

Oscillating ultralight scalar fields are a natural explanation for the dark matter in our Universe, as long as a mechanism, often called a misalignment mechanism, exists to explain the amplitude of the scalar oscillations. If the dark matter scalar couples to the Standard Model, then the dynamics of ordinary matter can influence the behavior of dark matter in the early Universe. In this work, we show how this changes the expected value of the scalar field and the resulting amplitude of late-time scalar oscillations and therefore the abundance of dark matter at late times. For dark matter scalars that interact quadratically with Standard Model fields, we derive estimates of the size of this effect as a function of the strength of the coupling, and for axionlike fields we show that interactions with dark sector matter can temporarily destabilize the field, leading to large field displacements.

We investigate the current viability of a well-known coupled dark energy scenario in which cold dark matter (CDM) interacts with a spin-0 dark energy component through a nontrivial field dependence of the dark matter (DM) mass. This ultralight scalar mediates a fifth force between DM particles, which can leave signatures on cosmological scales. We use state-of-the-art data on the cosmic microwave background from Planck’s camspec likelihood, baryon acoustic oscillations from the second DESI data release as well as the supernovae of Type Ia (SNIa) from $\mathrm{Pantheon}+\mathrm{and}$ DES-Dovekie. We perform the analysis considering both a flat potential and a Peebles-Ratra (PR) potential for the scalar field in order to assess the impact of the potential slope on the fitting performance of the model. While for a constant potential the scalar field dynamics is insensitive to the sign of the coupling parameter $\beta$, the PR potential breaks the existing symmetry in the solutions at late times and could induce a difference at the phenomenological level between positive and negative values. We study for the first time if it is actually the case, finding no important asymmetry in the fitting results, essentially due to shifts in other parameters, which can lead to significant compensating effects. In the light of the aforesaid datasets, we find in all cases a peak at $|\beta |\sim 0.03$—less pronounced than reported in some recent works—excluding the no-coupling scenario at $\sim 95\%$ CL at most. The model is able to explain an effective crossing of the phantom divide, with the equation-of-state parameter lying within the $2\sigma$ bands of model-agnostic reconstructions, albeit with important differences in the shape of the central curves. Our results are very robust under changes in the SNIa sample used in the analysis and is not significantly altered when we replace a constant potential with the PR one, although the latter is crucial to produce the aforesaid crossing. In passing, we also provide constraints obtained with the PR potential in the uncoupled case.

Universal relations provide a particularly useful way to extract physical information from neutron star observables in the presence of various uncertainties by reducing the dependence on uncertain model parameters and microphysical inputs. In this study, we examine the oscillation frequencies of mirror dark matter admixed neutron stars using a two-fluid description, where the outer and inner fluids give rise to two distinct fundamental frequencies. We confirm that the universal relation between the mass-scaled fundamental frequency of the outer-fluid-led mode and the stellar compactness, established previously for self-interacting dark matter admixed neutron stars, also holds in the mirror dark matter scenario. However, this universal relation becomes less robust when metric perturbations are included, compared with the corresponding results in the Cowling approximation. We further find that the inner-fluid-led fundamental frequency can also be expressed as a compactness-dependent relation that is largely independent of the normal matter equation of state, provided that the dark matter mass fraction is fixed. These results suggest that the simultaneous detection of the two fundamental frequencies could provide a way to constrain the dark matter mass fraction, even when the equation of state of normal matter remains uncertain. Finally, we find that the Cowling approximation estimates the fundamental frequency associated with the outer fluid with an accuracy comparable to that found for standard neutron stars without dark matter, while it performs even better for the frequency associated with the inner fluid.

By monitoring the times of arrival of radio pulses from millisecond pulsars, pulsar timing arrays (PTAs) serve as unique gravitational wave (GW) laboratories in the nanohertz band. To date, the primary astrophysical sources of GWs targeted in this frequency range have been inspiraling supermassive black hole binaries (SMBHBs) on circular and eccentric orbits. In this work, we demonstrate that, thanks to the so-called pulsar term in the timing residual waveform of GW signals, PTAs can probe individual SMBHBs that merged before timing observations began. We refer to the latter as zombie binaries. Using SMBHB population models consistent with current PTA constraints, we find that while the probability of detecting such systems in existing PTA datasets remains low, the Square Kilometer Array observatory is expected to achieve sufficient sensitivity to have a few zombie binaries with optimal matched filter signal-to-noise ratios exceeding 3 in its data. Although their confident identification might be challenging, this new class of PTA sources opens a novel window for studying the most massive SMBHBs in our local universe.

The equation-of-state (EOS) parameter $\varphi \equiv P/ϵ$, defined as the ratio of pressure to energy density, encapsulates the fundamental response of matter under extreme compression. Its value at the center of the most massive neutron star (NS), $\mathrm{X}\equiv P_{\mathrm{c}}/{ϵ}_{\mathrm{c}}$, provides an upper bound on the maximum attainable central EOS parameter of cold visible matter. Remarkably, owing to the intrinsically nonlinear structure of the EOS in general relativity (GR), this bound lies far below the naive special relativity (SR) limit of unity. In this work, we refine the theoretical upper bound on $\mathrm{X}$ in a self-consistent manner by incorporating, in addition to the causality constraint from SR, the mass-sphere stability condition associated with the mass evolution pattern in the vicinity of the NS center. This condition is formulated within the intrinsic and perturbative analysis of the dimensionless Tolman–Oppenheimer–Volkoff equations (IPAD-TOV) framework. The combined constraints yield an improved bound, $\mathrm{X}\lesssim 0.385$, which is slightly above but fully consistent with the previously derived causal-only limit, $\mathrm{X}\lesssim 0.374$. We further derive an improved scaling relation for NS compactness and demonstrate its robustness across a broad set of 284 realistic EOSs, including models with first-order phase transitions, exotic degrees of freedom, continuous crossover behavior, and deconfined quark cores. Within the IPAD-TOV framework, the resulting bound on $\mathrm{X}$ provides a new EOS-insensitive probe of the microphysics of cold superdense matter compressed by strong-field gravity in GR.

We study scalar field perturbations of a static and spherically symmetric spacetime describing a dyonic black bounce geometry. Depending on the electric and magnetic charges, the spacetime can represent either a regular black hole or a horizonless compact object. We derive the effective potential for massless scalar perturbations and analyze its structure for different parameter regimes. In the black hole phase, the quasinormal mode spectrum is calculated using the Wentzel-Kramers-Brillouin (WKB) approximation and compared with the eikonal formula derived from null geodesics. The two approaches show good agreement in the large multipole limit. When the charge parameters exceed a critical value, the event horizon disappears, and the spacetime becomes a horizonless compact object. In this case, the effective potential develops a characteristic double-barrier structure that forms a trapping cavity for perturbations. The time-domain evolution reveals the presence of the echoes produced by repeated reflections of waves inside this cavity. These results suggest that the dyonic black bounce geometry can naturally generate echo signals without introducing artificial boundary conditions, providing a possible observational probe to distinguish horizonless compact objects from classical regular black holes in gravitational-wave observations.

We present a framework to study the orientation distribution of nearby double white dwarf binaries with LISA, explicitly accounting for the fourfold degeneracy in the polarization angle. Exploiting the beltlike sky distribution of the nearby sample along the Galactic plane, we show that the low-multipole extraction can be recast as an effectively one-dimensional Fourier analysis along Galactic longitude, within a spherical-harmonic expansion based on the Wigner-$D$ formalism. The symmetry with respect to the Galactic plane governs the sensitivity: modes even under reflection across the plane remain accessible, while odd modes are strongly suppressed. For a fiducial sample of about 500 binaries within $\lesssim 4\mathrm{kpc}$, corresponding to roughly 5% of the resolved Galactic population, the method yields an uncertainty of order 0.02 for the reflection-even coefficients with $\ell \le 3$, and is readily applicable to the forthcoming LISA catalog.

All standard scalar quantum-information measures—concurrence, negativity, entanglement entropy, the optimized Clauser-Horne-Shimony-Holt bound, and quantum Fisher information—are $CP$ blind in ideal $\mathrm{spin}\text{−}0\to f\overline{f}$ decays because the two-qubit spin state is maximally entangled for every $CP$ angle. We show that the stabilizer Rényi entropy, evaluated in the physical Pauli frame of spin analysis, escapes this blind spot: it admits an exact closed form, vanishing at $CP$-definite and Clifford phases and peaking at maximal non-Clifford mixing. Two experimentally accessible, nonstabilizerness-inspired $CP$ witnesses follow; the linear amplitude is 14.3 times more efficient than its quartic counterpart and reaches discovery-level sensitivity at the HL-LHC for $H\to {\tau }^{+}{\tau }^{-}$.

We employ deep neural networks to represent the field derivative of the scale-dependent effective potential in the functional renormalization group (fRG) framework for nonperturbative quantum field theory. By embedding the fRG flow equations directly into the loss function, the network parameters are determined so as to provide a continuous and differentiable representation of the scale- and field-dependent effective potential without relying on precomputed training data. Focusing on the $O(N)$ scalar field theory within the local potential approximation at finite temperature, we demonstrate that this neural network representation accurately captures the renormalization group flow across symmetric, broken, and critical regimes. A key ingredient is a decomposition of the representation into an analytically known large-$N$ contribution and a learned finite-$N$ correction, which efficiently mitigates numerical stiffness associated with convexity restoration in the broken phase. The physics-driven solutions show excellent agreement with established finite-difference and discontinuous Galerkin methods. We further apply the same strategy to the Wilson-Fisher fixed-point equation in three dimensions, illustrating that neural network representations provide a unified framework for both scale-dependent flows and fixed-point problems. For fixed points, the large-field asymptotic form alone can replace the exact large-$N$ reference, while a composite small- and large-field ansatz further improves accuracy, extending the method to problems without an analytically solvable limit. Our results indicate that physics-driven deep learning offers a robust and flexible numerical tool for functional renormalization group studies.

The first study of charge-dependent two-particle differential number ($B$) and momentum balance functions ($P_2^{\mathrm{CD}}$) with respect to an event shape variable, transverse spherocity, is reported. Results are presented from pythia8 and epos-lhc model calculations in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$. To distinguish between back-to-back jetlike topologies and isotropic events, low and high transverse spherocity values are chosen. The correlation functions are measured as a function of charged-particle multiplicity classes in relative pseudorapidity ($\mathrm{\Delta }\eta$) and relative azimuthal angle ($\mathrm{\Delta }\varphi$) with $|\eta |<2.4$ and $0.2<p_{\mathrm{T}}<2.0\mathrm{GeV}$. A narrowing of the balance function width is observed in $\mathrm{\Delta }\eta$ and $\mathrm{\Delta }\varphi$ from low- to high-multiplicity collisions. Wider balance functions are found in isotropic events as compared to jet-like events. However, for the momentum correlations, a nearly flat dependence is observed with charged particle multiplicity. This study investigates charge conservation mechanisms and their correlations for events classified with jetlike and isotropic topologies. To isolate medium-driven effects, we compare epos-lhc with its hydrodynamic core enabled and disabled and observed narrowing patterns in $B$ and $P_2^{\mathrm{CD}}$ as a quantitative handle on radial-flow–induced localization of charge-balancing pairs.

Solving path integrals in quantum field theories often involves the numerical handling of noncommuting Grassmann fields, which is in many cases a highly nontrivial and numerically inefficient task, especially in large systems and at higher dimensions. In this paper a radial basis function type neural network construction is used to approximate fermionic path integrals that include local couplings in their hopping terms. By isolating the interaction terms from the purely fermionic components using a radial basis function expansion, the path integral can be approximated by a few percent accuracy even for very large lattice sizes. The method has been developed and tested using staggered fermions in one, and in two dimensions, through calculating the partition functions, and expectation values.

If the Universe underwent a cosmic phase transition, it may have left behind a network of cosmic strings. When these strings arise from the breaking of a gauge symmetry, their decay produces a significant stochastic background of gravitational waves. In contrast, if they originate from the breaking of a global symmetry, their decay predominantly yields Nambu-Goldstone bosons, which can persist as dark matter or dark radiation. In this work, we assess the detectability of this particle spectrum using a range of cosmological probes. We employ seminumerical methods to estimate the resulting energy density and compute the associated matter power spectrum. We then compare these predictions with observations of the cosmic microwave background, Lyman-$\alpha$ forest, large-scale structure surveys, and the UV luminosity function, thereby deriving constraints on the Nambu-Goldstone boson mass and the symmetry-breaking scale. Finally, we present projections for the sensitivity of upcoming cosmic microwave background missions.

We explore the sensitivity of the upcoming MAGIX experiment at the MESA facility to light Beyond the Standard Model (BSM) mediators in the few to hundred MeV mass range. Utilizing high-intensity electron beams of 55 MeV and 105 MeV on a heavy ${}^{181}\mathrm{Ta}$ target, we investigate the production of scalar, pseudoscalar, vector, and axial vector mediators via the Bethe-Heitler process. By optimizing the asymmetric kinematic acceptance of the double-spectrometer setup to enhance the signal over background ratio, we demonstrate that MAGIX can probe mediator-electron couplings down to $\mathcal{O}({10}^{-4})$, offering a competitive probe of the dark sector in the sub-GeV mass range.

Electroweak triplet Higgs sector extensions are well-motivated scenarios to address lepton flavor observations. These models can also be strongly constrained by combining precise, indirect low-energy measurements with direct searches for exotic, doubly-charged Higgs bosons. Together, these searches set competitive constraints on the type-II seesaw mechanism. In this work, we consider extensions of the type-II seesaw, specifically through the lens of a modified collider phenomenology. Surveying motivated extensions, we map out changes in expected correlations, focusing on the modified production and decay phenomenology of exotic Higgs particles. This enables us to assess the robustness of the type-II seesaw collider constraints against extended new-physics contributions that modify standard sensitivity expectations and projections.

Leptophilic dark matter (DM) is a well-motivated thermal weakly interacting massive particle framework that can evade stringent nuclear-recoil searches while remaining testable via DM-induced heating of neutron stars (NSs). In this work, we study leptophilic scalar DM in a $\mathrm{U}(1{)}_{L_{\mu }-L_{\tau }}$ gauge extension of the Standard Model, which provides a common leptophilic portal for all scenarios considered. To reproduce the observed relic abundance while suppressing direct-detection signals, we investigate three benchmark realizations: (i) a secluded DM scenario in which the relic density is set by annihilation into $\mathrm{U}(1{)}_{L_{\mu }-L_{\tau }}$ gauge bosons and two pseudo-Nambu-Goldstone boson (pNGB) DM models based on (ii) an SO(4) symmetry and (iii) an SO(3) symmetry. In the SO(4) pNGB model, the DM mass arises at tree level from a soft breaking term, while the elastic scattering amplitude is suppressed by a symmetry-protected cancellation. In the SO(3) pNGB model, the DM mass is generated radiatively at one loop via the $\mathrm{U}(1{)}_{L_{\mu }-L_{\tau }}$ gauge interaction, and we show that this gauging preserves the same cancellation mechanism, maintaining compatibility with direct-detection null results. We perform a systematic parameter scan imposing relic density, direct and indirect detection, and neutrino trident constraints and identify viable sub-TeV to TeV DM candidates. Under the optimistic maximal-heating assumption that the capture rate reaches the geometric limit and that the captured DM population efficiently thermalizes and attains capture-annihilation equilibrium inside NSs, we find that the remaining parameter space can be tested by near-infrared observations of old NSs, providing sensitivity complementary to terrestrial searches in regions that are currently weakly constrained.

Relativistic wavefunctions of nucleon excitations are scrutinized to understand their node structure and the underlying role of local interpolating fields in generating the nucleon spectrum. In addressing quark model perspectives, approximately 4000 propagators are employed on the heaviest PACS-CS ensemble at $m_{\pi }\simeq 702\mathrm{MeV}$. We examine the ground and four lowest-lying excited states at zero momentum for both positive- and negative-parity spectra, where the proton’s $d$-quark wavefunction is calculated about the two $u$ quarks at the origin. This is achieved using two local interpolating fields that each carry the quantum numbers of the nucleon but with differing spin-flavor structures, one of which vanishes in the nonrelativistic limit. We find that two distinct types of wavefunction nodes are manifest: “superposition nodes” formed through a linear combination of interpolating fields and novel “built-in nodes” that are fundamentally built in to the $s$-wave Dirac components of an individual interpolating field. These are investigated qualitatively through visualizations in the form of both volume and surface renderings and quantitatively by the calculation of radial wavefunctions. Combined, these findings build a comprehensive picture of the single-particle nucleon spectrum and how its properties derive from fundamental lattice operators.

We present a solvable Hamiltonian that realizes an exact lattice chiral ${\mathrm{U}(1)}_{\mathrm{V}}\times {\mathrm{U}(1)}_{\mathrm{A}}$ symmetry. Nielsen-Ninomiya-type no-go theorems are evaded by using lattice bosons rather than fermions. The continuum limit is a compact boson field theory with an axionlike coupling. The ${\mathrm{U}(1)}_{\mathrm{V}}$ symmetry shifts the scalar, while ${\mathrm{U}(1)}_{\mathrm{A}}$ acts on local operators associated with short axion strings and is transmuted into a higher-form symmetry in the continuum limit. We demonstrate the chiral anomaly by showing that the lattice theta angle is shifted by an axial rotation when ${\mathrm{U}(1)}_{\mathrm{V}}$ is gauged. Gauging either ${\mathrm{U}(1)}_{\mathrm{V}}$ or ${\mathrm{U}(1)}_{\mathrm{A}}$ leads to lattice noninvertible and 2-group symmetries, respectively, matching the continuum picture.

We study the analytic structure of the QCD phase diagram by treating temperature as a complex variable. The nearest Yang-Lee edge singularities in the complex-$T$ plane bound the domain of analyticity of temperature-dependent thermodynamic observables and complement the more commonly studied singularities in the complex chemical-potential plane. Our analysis combines three complementary perspectives: universal critical scaling, a first-principles extraction from lattice-QCD data, and explicit illustrations in effective models. We illustrate the resulting structure in a random-matrix model and in a quark-meson model, where the singularity trajectories can be followed explicitly. At small real chemical potential, the leading complex-temperature singularity admits an analytic expansion in ${\mu }^2$, while near a critical point it crosses over to the universal Puiseux form dictated by Ising critical scaling. We show that the complex-$T$ and complex-$\mu$ trajectories are controlled by the same scaling variables and mapping coefficients, so their comparison provides a stringent consistency test of critical-point searches and constrains the extent of the critical scaling regime. Finally, we analyze lattice-QCD data at $\mu =0$ using an iterated conformal-Padé approach and extract the continuum location of the nearest complex-temperature singularity. The result is consistent with the expectation that, at physical quark masses, the real part of the leading singularity lies between the chiral-limit transition temperature and the physical-mass chiral-susceptibility peak temperature, while its imaginary part remains nonzero.