Self-interacting dark matter (SIDM) theories predict that dark matter halos experience core-collapse in late-stage evolution, a process where the halo’s inner region rapidly increases in density and decreases in size. This process can be modeled by treating the dark matter as a gravothermal fluid, and solving the fluid equations to predict the density profile evolution. This model is incomplete without calibration to $N$-body simulations, through a constant factor $\beta$ included in the thermal conductivity for the long-mean-free-path limit. The value of $\beta$ employed in the gravothermal fluid formalism has varied between studies, with no clear universal value in the literature. In this work, we use the $N$-body code arepo to conduct a series of isolated core-collapse simulations across a range of scattering cross sections, halo concentrations, and halo masses to calibrate the heat transfer parameter $\beta$. We find that $\beta$ is independent of cross section, halo concentration, and halo mass for velocity independent elastic scattering cross sections. We present a model for an effective $\beta$ as a function of a dimensionless cross section, to describe halo evolution in the long mean free path limit, and show that it accurately captures halo evolution as long as the cross section is not too large. This effective model facilitates comparisons between simulations and the gravothermal model and enables fast predictions of the dark matter density profile at any given time without running $N$-body simulations.

Perturbation theory, as well as most thermal field resummation methods widely used to study finite-temperature quantum field theories, presents a non-negligible renormalization scale dependence. To address this limitation, we propose an alternative method that combines the renormalization group improvement prescription for the thermal effective potential with the optimized perturbation theory variational resummation technique. Here, we apply this new framework, termed variational renormalization group, to evaluate the effective potential of the scalar $\lambda {\varphi }^4$ theory at finite temperatures, which represents a benchmark model for phase transition studies. We show that the proposed approach significantly improves scale stability, compared to the use of optimized perturbation theory alone, across key thermodynamic quantities, including the effective potential, critical temperature, and pressure. These results establish the variational renormalization group as a robust alternative tool for precision studies of thermal phase transitions, with direct implications for cosmological applications (e.g., early-Universe thermodynamics) and condensed matter systems.

In this work, we study leptonic decays of hadrons as probes of light neutrinophilic scalars that mediate enhanced neutrino self-interactions. Such scalars can be emitted in processes involving neutrinos, turning two-body decays into three-body final states and producing characteristic spectral distortions. We compute these effects for charged pion decay and nuclear electron capture decay, including both on-shell and off-shell scalar emission, as well as the loop-induced renormalization required to cancel divergences. Using these results, we derive the projected sensitivity of PIONEER and assess the current and future reach of BeEST. The resulting low-energy spectral tails provide a characteristic signal for light neutrinophilic scalars, making upcoming hadron decay experiments powerful probes of light mediators of nonstandard neutrino self-interactions.

We investigate a scenario where strongly interacting massive particle (SIMP) dark matter interacts with an axionlike particle (ALP) that couples exclusively to electrons. This minimal setup provides interactions which enforce thermal equilibrium between dark matter and the standard model (SM) in the early Universe. We analyze the cosmological evolution of the dark sector and the constraints arising from dark matter annihilations, ALP laboratory searches and astrophysical observations. Our results show that the allowed parameter space is wider than previous studies and an ALP with mass $m_a\sim \mathcal{O}(10)\mathrm{MeV}$ can act as a viable portal between the visible and dark sectors. Interestingly, this mass range overlaps with the parameter space suggested by the reported $X_{17}$ anomaly. Furthermore, the introduction of nonvanishing $\theta$ angle in the dark sector of the model opens up the parameter space to heavy ALP masses.

Minimal flavor violation (MFV) provides a compelling framework for exploring physics beyond the Standard Model, in which new QCD-singlet fields transforming under the global $\mathrm{SU}(3{)}^3$ quark flavor symmetry can naturally be stable and act as dark matter (DM) candidates. We show that the DM–MFV framework naturally accommodates the excess in either $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ or $B^{+}\to K^{+}\nu \overline{\nu }$, while a unified explanation of both channels simultaneously cannot be achieved within a minimal setup containing only a single dark matter multiplet with nearly degenerate masses. Overall, our findings underscore the intricate interplay between MFV-based model building, flavored dark matter scenarios, and precision flavor experiments, highlighting flavored dark matter as a framework that is both theoretically robust and experimentally testable.

The Cabibbo-favored decay ${\mathrm{\Lambda }}_c^{+}\to n{\overline{K}}^0{\pi }^{+}$ offers a unique window to explore unresolved puzzles in the low-energy baryon spectroscopy and the isospin dynamics of the $\overline{K}N$ system. Recent experimental results present a, for now, contradiction: LHCb and Belle analyses of ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ suggest the $p{K}^{-}$ ($I=0$) component dominates, while the Beijing Spectrometer III (BESIII) hints at significant contributions from both isospin 0 and 1 in the $n{\overline{K}}^0$ system of ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$. Furthermore, the measured branching fraction of ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$ exceeds SU(3) symmetry predictions by a factor of 3–4, signaling strong contributions from low-lying resonances. In this work, we provide a theoretical analysis of ${\mathrm{\Lambda }}_c^{+}\to n{\overline{K}}^0{\pi }^{+}$ within the coupled-channel chiral unitary approach, where the $N(1535)$ and $\mathrm{\Lambda }(1670)$ can be dynamically generated. Our calculations show a narrow peak from $N(1535)$ in the ${\pi }^{+}n$ invariant mass spectrum and a distinct dip from $\mathrm{\Lambda }(1670)$ in the ${\overline{K}}^{0}n$ spectrum. The dip structure is qualitatively consistent with the $\mathrm{\Lambda }(1670)$ manifestation in $\overline{K}N\to \overline{K}N$ scattering, supporting its molecular interpretation. This study not only connects the experimental observations but also highlights ${\mathrm{\Lambda }}_c^{+}\to n{\overline{K}}^0{\pi }^{+}$ as a crucial process to disentangle the nature of $N(1535)$ and $\mathrm{\Lambda }(1670)$. Future precise measurements of this decay channel by the BESIII, Belle II, LHCb, and the proposed Super Tau-Charm Facility are strongly encouraged.

To decode the near-threshold dynamics of the $X_{0,1}(4140)$ and $X_1(4685)$ states, we investigate the OZI-suppressed $\{D_s{\overline{D}}_s,J/\psi \varphi ,D_s^{*}{\overline{D}}_s^{*}\}$ coupled-channel scattering in $B\to D_s{\overline{D}}_{s}K$ decays using the effective range expansion. We demonstrate that the $X_0(4140)$, associated with a dip in the line shape, corresponds to a dynamically generated pole near the $J/\psi \varphi$ threshold. The single-channel $J/\psi \varphi$ scattering length is extracted to be $1.11\pm 0.65\mathrm{fm}$, yielding an effective scattering length of ${0.12}_{-0.10}^{+0.20}+i0.78_{-0.40}^{+0.20}\mathrm{fm}$ when coupled channels are included. By treating the spin-spin interaction as a subleading effect, we predict a $J^{PC}=1^{++}$ virtual state near the $J/\psi \varphi$ threshold, which naturally resolves the empirical ambiguities surrounding the $X_1(4140)$ width. Extending this framework via heavy quark spin symmetry, we further interpret the $X_1(4685)$ as a $\psi (2S)\varphi$ hadronic molecule. Ultimately, these findings highlight how the $X(4140)$ family and $X_1(4685)$ serve as unique theoretical windows into the Fierz rearrangement and OZI suppression mechanisms in low-energy strong interactions.

In previous papers we developed the light front formulation for Hamiltonians and wave functions (WFs) for mesons and baryons, with both confinement and chiral symmetry breaking. For baryons limited to the lowest Fock component with three quarks, the longitudinal WF is valued in an equilateral triangle with momentum fractions $x_i,i=1$, 2, 3. In this paper we extend this analysis to light quark pentaquarks ($n=5$) at angular momenta $L=0$ and $L=1$, in which case the longitudinal WF is defined on 4d simplex $A_4$ with 5 corners. The WF was developed both numerically and using a basis function that diagonalizes the Laplacian with Dirichlet boundary conditions. From the WF follows many predictions, we discuss PDFs of antiquarks specifically. We then focus on mixing between baryons with 27 $L=1$ pentaquark states, via two operators related to adding pionlike and sigmalike $\overline{q}q$ pairs. While similar mechanisms of introduction of nonzero angular momentum and flavor asymmetry of the antiquark sea was discussed before, our pentaquark-based approach is unique in providing WFs with full Fermi statistics of 4 quarks.

We extend our previous work on the energy loss of a heavy fermion in a QED plasma to the quark-gluon plasma, using the same Bhatnagar-Gross-Krook collisional kernel. The calculation is carried out with a theoretical method where the hard-thermal-loop resummed gluon propagator is used for arbitrary momentum transfer in the scattering processes. Encoding the collision effect in a self-consistent manner, the resummed gluon propagator regulates the infrared divergence in the scattering amplitude without introducing an artificial cutoff for the transferred momenta and makes the analysis on the hard and soft processes in a unified framework. To place our computation on a more solid foundation, we also explicitly demonstrate the gauge independence of the interaction rate as well as the elimination of unphysical gluon polarizations by the ghost field under the use of the resummed gluon propagator. In addition, with our complete QCD calculation by including both quark-quark and quark-gluon scatterings, we provide a quantitatively reliable result on the collisional energy loss of a heavy quark where the new contribution from quark-gluon scatterings accounts for a larger portion of the total energy loss. In general, collisions between the thermal partons result in an increased energy loss which becomes more pronounced with increasing gauge coupling. Considering a typical coupling constant in QCD, ${\alpha }_s=0.3$, the energy loss increases $\sim 8\%$ at large incident velocities as compared to the collisionless limit. Such a collision-induced correction is still moderate, although it is slightly suppressed as compared to our previous estimate based on a QED calculation using couplings consistent with those expected to be generated in the quark-gluon plasma.

Heavy particle effective theory applied to spinning black holes provides a natural framework in which propagators linearize and numerators exponentiate. In this work, we exploit these two features to introduce Kerr generating functions, which describe the scattering of any probe on a Kerr black hole background to all loop orders. These generating functions can be used to perform the tensor reduction of multiloop integrands simply by differentiation with respect to the spin. As a first application of the Kerr generating functions, we study the leading nonlinear tidal effects of a neutron star in a Kerr black hole background. We organize the integrand by the helicity configuration of the exchanged gravitons and provide compact all-loop-order results for several helicity sectors and a full four-loop $\mathcal{O}(G^5)$ result for the leading nonlinear tidal operators.

Next-generation ground-based gravitational wave (GW) detectors are expected to observe millions of binary black hole mergers, a fraction of which will be strongly lensed by intervening galaxies or clusters, producing multiple images with characteristic distribution of time delay. Importantly, the predicted rate and properties of such events are sensitive to the abundance and distribution of strong lensing objects which directly depends on cosmological models. One such scenario posits the existence of supermassive primordial black holes (SMPBHs) in the early Universe, which would enhance the formation of dark matter halos. This mechanism has been proposed to explain the abundance of high-redshift galaxies observed by James Webb Space Telescope. Crucially, the same cosmological model with SMPBHs would also leave a distinct imprint on the population of strongly lensed GWs. It predicts both an increased event rate and a modified distribution of time delays between the multiple images. Therefore, we propose statistical measurements of the rate and time delay distribution of strong lensing GW events as a powerful probe to directly constrain the abundance of SMPBHs. Considering $\mathrm{\Lambda }\mathrm{CDM}$ cosmology with (non)clustered SMPBHs, we find that the abundance of SMPBHs $f_{\mathrm{PBH}}$ with masses above ${10}^8{M}_{\odot }$ is constrained to be $\sim {10}^{-4}$ at 95% confidence level. It will be comparable and complementary to the currently available constraint from large scale structure observations.

We investigate the effective potential and the string tension for the spatial Wilson loop in hot dense quark-gluon plasma with two types of anisotropy, i.e., external magnetic field and spatial anisotropy, employing a holographic approach for the heavy quark model. In this approach, the string is extended in the fifth, holographic direction and has a turning point either on a dynamical wall (DW) configuration or on the horizon configuration in the fifth direction. We obtain the magnetic catalysis behavior for a phase transition between DW and horizon configuration of the string. The structure of the phase diagram does not depend on the boundary conditions choice for the dilaton field. Inclusion of the external magnetic field and spatial anisotropy enhance the string tension in the horizon configuration, namely drag force. For the spatially isotropic case $\nu =1$ at different magnetic field values, the string tension is proportional to $T^2$ and is qualitatively consistent with lattice results. However, for the anisotropic case, $\nu =4.5$, it deviates from the quadratic term.

We study the asymptotic symmetries of the Nappi-Witten spacetime in four dimensions, a plane wave arising as the Penrose limit of ${\mathrm{AdS}}_2\times S^2$. Imposing suitable boundary conditions at large transverse distance, we uncover a new infinite-dimensional symmetry algebra allowing for nontrivial central extensions. The corresponding phase space encompasses the most general four-dimensional pp-wave metric, including in particular the Penrose limit of Kerr black holes.

It has recently been suggested that exotic quantum gravity effects could lead to large vacuum fluctuations, potentially observable with realistic detectors. Experiments are currently being built to search for these signals. Here we analyze the minimal model of quantum gravity at low energies—the usual effective quantum field theory of gravitons—and show that it unambiguously predicts an unobservably small variation in the measured interferometer length $\mathrm{\Delta }L\sim {\ell }_{\mathrm{pl}}\sim {10}^{-35}\mathrm{m}$. In particular, there are no divergences signaling a breakdown of this calculation in the low energy regime. Thus, detection of a large, gravitationally induced length variation would signal a severe breakdown of effective quantum field theory in low energy quantum gravity.

The frozen star is a type of black hole mimicker; an ultracompact object whose exterior geometry resembles that of a general relativistic black hole but differs in its matter composition and in the regularity of its interior geometry. It is sourced by a spherically symmetric collection of open-string flux tubes, which posses an extremely anisotropic energy-momentum-stress tensor with maximally negative radial pressure. The frozen star represents an effective classical description of the highly quantum, closed-string polymer model. A key challenge for any model of a black hole mimicker is to explain how such objects can form from a collapsing body of matter. We started to address this important problem in [1] by adapting the Euclidean-action method of Gibbons and Hawking to show that the transition into a frozen star is likely. Here, we improve on our previous results by showing that the transition probability for a collapsing shell of matter to tunnel quantum mechanically into a frozen star is unity, up to negligible corrections. Our conclusion is that such a transition is therefore inevitable.

The nature of dark energy is one of the big puzzling issues in cosmology. While $\mathrm{\Lambda }\mathrm{CDM}$ provides a good fit to the observational data, evolving dark energy scenarios, such as the CPL parametrization, offer a compelling alternative. In this paper, we present a Bayesian model comparison of various dark energy parametrizations using a joint analysis of cosmic microwave background data, DESI baryon acoustic oscillation measurements, and the PantheonPlus (or Union3) Supernovae type Ia sample. We find that while the $\mathrm{\Lambda }\mathrm{CDM}$ model is initially favored over a constant $w\mathrm{CDM}$ model, the CPL parametrization is significantly preferred over $w\mathrm{CDM}$, reinforcing recent evidence for an evolving dark energy component, consistent with DESI Collaboration findings. Crucially, when testing higher-order CPL extensions, the so-called ${\mathrm{CPL}}^{+}$ and ${\mathrm{CPL}}^{++}$, our Bayesian analysis shows that the observational data do not favor these more complex scenarios compared to the standard CPL. This result indicates that adding excessive complexity to the CPL form is unwarranted by current observations. Interestingly, similar to the CPL parametrization, alternative two-parameter forms, specifically $w_{de}(a)=w_0+w_b(1-a{)}^2$ and $w_{de}(a)=w_0+w_c(1-a{)}^3$, yield a better fit to observational data than the standard $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. Our results challenge the necessity for overly complex CPL extensions and confirm that well-chosen two-parameter $w_0{w}_a$ parametrizations effectively capture DE evolution with current cosmological data, supporting the recent signals for dynamical dark energy by DESI Collaboration.

We establish a void-based consistency test for Galileon scalar-tensor theories. We show that the previously reported unphysical breakdown of the predicted Newtonian force in certain Galileon models is controlled by a single condition linking nonlinear void dynamics to the cosmic expansion history. This connection yields a redshift-dependent upper bound on the allowed depth of voids and promotes this requirement to a new viability condition, complementary to standard stability criteria. As an example, we apply this void-based criterion to a linear parametrization in the scale factor constrained by theoretical and observational bounds; we find that $\sim 60\%$ of the parameter space is excluded, with most problematic models failing by $z\lesssim 10$. These results position cosmic voids as sharp, complementary, and theory-informed filters for viable modified gravity, enabling more informed priors and parameter-space choices in future cosmological inference.

The decay of light bosonic dark matter particles can produce a bright electron/positron ($e^{+}{e}^{-}$) flux that can be strongly constrained by local Voyager observations of the direct $e^{+}{e}^{-}$ flux, as well as 511 keV line and x-ray continuum observations of $e^{+}{e}^{-}$ emission. We carefully analyze the $e^{+}{e}^{-}$ yield and resulting cosmic ray and x-ray spectra from theoretically well-motivated light dark matter models, including (a) electrophilic axion-like particles, (b) dark photons, (c) scalars, and (d) $B-L$ and $L_i-L_j$ vector bosons. We use the morphology and spectrum of the INTEGRAL 511 keV line data, the eROSITA x-ray continuum spectrum and the Voyager $e^{+}{e}^{-}$ spectrum to constrain the decay lifetime and coupling of each dark matter model. We find that 511 keV observations typically set world-leading limits on bosonic dark matter decay below masses of $\sim 1\mathrm{GeV}$, while eROSITA observations provide the strongest constraints in the range from 1–10 GeV. Finally, we forecast future limits from 21 cm line searches with next-generation HERA data.

The scattering of dark matter (DM) particles within the Sun’s hot plasma can lead to the acceleration of dark matter, producing a high-energy solar-reflected DM flux detectable in ground-based experiments. In the vector portal model, the dark matter has a sub-MeV-scale mass, and interactions between the dark matter and Standard Model particles are mediated by a hidden vector field—referred to as a dark photon—which kinetically mixes with the conventional photon through a small mixing angle. Furthermore, the solar plasma generates intense magnetic fields. Due to the photon-dark photon mixing, this simultaneously sources a “dark magnetic field.” For sufficiently low dark photon masses, this dark magnetic field is capable of deflecting dark matter particles traversing the Sun. We found that if the dark magnetic force is sufficiently strong, the dark magnetic field becomes a wall, preventing the dark matter particles from reaching the deep core region, suppressing their reflected flux. This scenario corrects the sensitivity of the solar-reflected dark matter detection, offering critical insights for ground-based experiments aiming to probe dark matter.