We investigate the cosmological impact of hypothetical unstable new physics particles that decay in the MeV-scale plasma of the early Universe. Focusing on scenarios where the decays produce metastable species such as muons, pions, and kaons, we systematically analyze the dynamics of these particles using coupled Boltzmann equations governing their abundances. Our results demonstrate that the metastable species can efficiently annihilate or interact with nucleons, often leading to their disappearance before decay. The suppression of decay significantly alters the properties of cosmic neutrinos, impacting cosmological observables like big bang nucleosynthesis and the cosmic microwave background. To support further studies, we provide two public codes: the Mathematica code that traces the evolution of these metastable particles, as well as the python-based unintegrated neutrino Boltzmann solver that uses this evolution as an input and may be applied to a broad range of scenarios. We then utilize them for studying a few particular new physics models.

Descriptions of the Galactic Center using Fermi gamma-ray data have so far modeled the Galactic Center excess (GCE) as a template with fixed spatial morphology or as a linear combination of such templates. Although these templates are informed by various physical expectations, the morphology of the excess is a priori unknown. For the first time, we describe the GCE using a flexible, nonparametric machine learning model—the Gaussian process (GP). We assess our model’s performance on synthetic data, demonstrating that the model can recover the templates used to generate the data. We then fit the Fermi data with our model in a single energy bin from 2–20 GeV (leaving a spectral GP analysis of the GCE for future work) using a variety of template models of diffuse gamma-ray emission to quantify our fits’ systematic uncertainties associated with diffuse emission modeling. We interpret our best-fit GP in terms of GCE templates consisting of an Navarro-Frenk-White (NFW) squared template and a bulge component to determine which bulge models can best describe the fitted GP and to what extent the best-fit GP is described better by an NFW squared template versus a bulge template. The best-fit GP contains morphological features that are typically not associated with traditional GCE studies. These include a localized bright source at around $(\ell ,b)=(20°,0°)$ and a diagonal arm extending Northwest from the Galactic Center. In spite of these novel features, the fitted GP is explained best by a template-based model consisting of the bulge presented in Coleman et al. (2020) and a squared NFW component. Our results suggest that the physical interpretation of the GCE in terms of stellar bulge and NFW-like components is highly sensitive to the assumed morphologies, background models, and the region of the sky used for inference.

Ultralight bosons with masses in the range from $\sim {10}^{-22}\mathrm{eV}/c^2$ to $\sim 1\mathrm{eV}/c^2$, are well-motivated, wavelike dark matter candidates. Particles on the lower-mass end are less explored in experiments due to their vanishingly small mass and weak coupling to the Standard Model. We propose a sensor with dual torsion pendulums for the direct detection of ${\mathrm{U}(1)}_{B-L}$ gauge boson dark matter, which can achieve an enhanced differential torque sensitivity in a frequency band of $\sim {10}^{-2}–10\mathrm{Hz}$ due to its advantages in common-mode rejection and differential angular sensitivity. We describe the design of the differential torsion sensor and present the estimated sensitivity to an ultralight dark matter field coupled to baryon minus lepton ($B-L$) number, in a mass range of $\sim {10}^{-17}–{10}^{-13}\mathrm{eV}/c^2$. Given a setup with meter-scale torsion pendulum beams and kg-scale test masses, the projected constraints on the coupling constant $g_{B-L}$ can reach $\sim {10}^{-27}$ for a boson mass of $\sim {10}^{-15}\mathrm{eV}/c^2$.

Modeling noise in gravitational-wave observatories is crucial for accurately inferring the properties of gravitational-wave sources. We introduce a transdimensional Bayesian approach to characterize the noise in ground-based gravitational-wave observatories using the Bayesian inference software bilby. The algorithm models broadband noise with a combination of power laws; narrow-band features with Lorentzians; and shapelets to capture any additional features in the data. We show that our noise model provides a significantly improved fit of the Laser Interferometer Gravitational-Wave Observatory and Virgo noise amplitude spectral densities compared to currently available noise fits obtained with on-source data segments. We perform astrophysical inference on well-known events in the third Gravitational-Wave Transient Catalog using our noise model and observe shifts of up to 7% in the 90% boundaries of credible intervals for some parameters. We discuss plans to deploy this framework systematically for gravitational-wave inference along with possible areas of improvement.

An ongoing challenge for radio-based detectors of high-energy cosmic particles is the accurate description of radio signal propagation in natural nonuniform media. For radio signals originating from extensive air showers, the current state of the art simulations often implicitly assume straight-line signal propagation. The refraction due to a nonuniform atmosphere is however expected to have an effect on the received signal and associated reconstruction. This effect is currently not completely understood for the most inclined geometries. Here, we present a study regarding the validity of straight-line signal propagation when simulating radio emission associated with very inclined air shower geometries. To this end, the calculation of the electric field based on the end point formalism used in coreas was improved by use of tabulated ray tracing data. We find a difference of 2% in radiation energy and a difference of $O(0.01°)$ on direction reconstruction when working at frequencies below 600 MHz. We thus find that, for frequencies up to 600 MHz and zenith angles up to 88°, the current straight-line based simulation approaches are accurate.

Gravitational lensing in wave optics is a rich field combining caustic singularities, general relativity and interference phenomena. We present a detailed evaluation of wave optics effects resulting from the frame-dragging of a rotating star modeled by a Lense-Thirring spacetime. We demonstrate that, contrary to what was previously stated in the literature (see e.g. [C. Baraldo et al., Phys. Rev. D 59, 083001 (1999)]), the spin of the star leaves an intricate imprint on the interference fringes and the caustics of the lensed source. This interference pattern can in principle be used to directly measure the spin of the lens.

The gravitational-lensing parallax of gamma-ray bursts (GRBs) is an intriguing probe of primordial black hole (PBH) dark matter in the asteroid-mass window, $2\times {10}^{-16}{M}_{\odot }\lesssim M_{\mathrm{PBH}}\lesssim 5\times {10}^{-12}{M}_{\odot }$. Recent work in the literature has shown exciting potential reach for this “picolensing” signal if a future space mission were to fly two x-/$\gamma$-ray detectors in the Swift/BAT class, with interspacecraft separation baselines on the order of the Earth–Moon distance. We revisit these projections with a view to understanding their robustness to various uncertainties related to GRBs. Most importantly, we investigate the impact of uncertainties in observed GRB angular sizes on reach projections for a future mission. Overall, we confirm that picolensing shows great promise to explore the asteroid-mass window; however, we find that previous studies may have been too optimistic with regard to the baselines required. Detector baselines on the order of at least the Earth–L2 distance would make such a mission more robust to GRB size uncertainties; baselines on the order of an astronomical unit (AU) would additionally enable reach that equals or exceeds existing microlensing constraints up to $M_{\mathrm{PBH}}\sim 2\times {10}^{-8}{M}_{\odot }$.

The XENONnT experiment, located at the INFN Laboratori Nazionali del Gran Sasso, Italy, features a 5.9 tonne liquid xenon time projection chamber surrounded by an instrumented neutron veto, all of which is housed within a muon veto water tank. Because of extensive shielding and advanced purification to mitigate natural radioactivity, an exceptionally low background level of $(15.8\pm 1.3)\mathrm{events}/(\mathrm{tonne}·\mathrm{year}·\mathrm{keV})$ in the (1,30) keV region is reached in the inner part of the time projection chamber. XENONnT is, thus, sensitive to a wide range of rare phenomena related to dark matter and neutrino interactions, both within and beyond the Standard Model of particle physics, with a focus on the direct detection of dark matter in the form of weakly interacting massive particles. From May 2021 to December 2021, XENONnT accumulated data in rare-event search mode with a total exposure of one $\mathrm{tonne}·\mathrm{year}$. This paper provides a detailed description of the signal reconstruction methods, event selection procedure, and detector response calibration, as well as an overview of the detector performance in this time frame. This work establishes the foundational framework for the “blind analysis” methodology we are using when reporting XENONnT physics results.

We carry out a comprehensive investigation on the radiative decays of $P$-wave bottom baryons using the light-cone sum rule method. We analyze their electromagnetic transitions into ground-state bottom baryons together with a photon. Together with their mass spectra and strong decays investigated in Tan et al. [Eur. Phys. J. C 84, 382 (2024)] and Yang and Chen [Phys. Rev. D 101, 114013 (2020)], a rather complete quantum chromodynamics (QCD) sum rule study has been done to understand the $P$-wave singly bottom baryons within the framework of heavy quark effective theory. As summarized in Tables VII and VIII, some $P$-wave bottom baryons have limited strong decay widths so that their radiative decay widths become non-negligible. We propose to study these excited bottom baryons and their radiative decays in the future Belle-II, BESIII, and LHCb experiments.

The standard Feynman rules used for perturbative calculations in quantum chromodynamics (QCD) are derived from a Lagrangian that is first-order in derivatives. It includes a three-point quark-gluon vertex which obscures the precise disentangled manner in which spin and momentum are interchanged during these interactions. An unambiguous understanding of this interchange is insightful for efficiently extracting physically relevant information from various Green’s functions. To separate the scalar and spin degrees of freedom and gain physical insight from the outset, we examine the quark-gluon vertex using the less commonly employed second-order formalism of QCD. We compute this off-shell vertex in arbitrary space-time dimensions and covariant gauges by using scalar integrals with shifted dimensions, which include higher powers of the propagators, within a combined first- and second-order formalism. This approach naturally identifies the transverse components of the quark-gluon vertex, even before evaluating the tensor Feynman integrals. Our results are in complete agreement with those obtained from the first-order formalism. We also compute the on-shell version of this vertex using exclusively the second-order formalism, facilitating a precise identification of spin and momentum interchange. Through analyzing the Pauli form factor at $k^2=0$ (where $k$ represents the momentum of the external gluon), we find that only a specific set of second-order Feynman diagrams are relevant for calculating the electromagnetic and chromomagnetic dipole moments. These diagrams represent quantum processes in which the spin of the incoming quark changes only once due to interactions with the virtual gluons that form the quark-gluon vertex. All other interactions involve only momentum interchange (scalar interactions). Furthermore, we confirm existing results in the literature, which suggest that defining the chromomagnetic dipole moment in the limit $k^2\to 0$ leads to infrared divergences.

We investigate a pseudo-Nambu-Goldstone (pNG) dark matter (DM) model based on a gauged $SU(2{)}_x$ and a global $SU(2{)}_g$ symmetries. These symmetries are spontaneously broken to a global $U(1{)}_D$ symmetry by a vacuum expectation value of an $SU(2{)}_x\times SU(2{)}_g$ bifundamental scalar field. The global $SU(2{)}_g$ symmetry is also softly broken to a global $U(1{)}_D$ symmetry. Under the setup, a complex pNG boson arises. It is stabilized by $U(1{)}_D$ and is a DM candidate. Its scattering cross section off a nucleon is highly suppressed by small momentum transfer and thus evades the stringent constraints from DM direct detection experiments. Assuming all the couplings in the dark sector are real, a discrete symmetry arises. Consequently, in addition to the pNG DM, the lighter one of an $SU(2{)}_x$ gauge boson $V^0$ and a $CP$-odd scalar boson $a_0$ from the bifundamental scalar field can also serve as a DM candidate. Therefore, the model provides two-component DM scenarios. We find that the relic abundance of the DM candidates explains the measured value of the DM energy density. We also find that the pNG DM is the dominant DM component in large regions of the parameter space. In contrast to the pNG DM, both $V^0$ and $a_0$ scatter off a nucleon, and their scattering cross sections are not suppressed. However, their scattering event rates are suppressed by their number densities. Thus, the scattering cross section is effectively reduced. We show that the effective DM-nucleon scattering cross sections in the two-component scenarios are smaller than the current upper bounds and above the neutrino fog.

We investigate a dark matter model that couples to the standard model through a one-loop interaction with neutrinos, where the mediator particles also generate neutrino masses. We perform a global fit that incorporates dark matter relic abundance, primordial nucleosynthesis, neutrino mass, collider, and indirect detection constraints. Thanks to the loop suppression, large couplings are allowed, and we find that the model parameters are constrained on all sides. Dark matter masses from 10 MeV to a few TeV are allowed, but sub-GeV masses are preferred for the model to also account for the heaviest neutrino mass. Though our results are valid for a single neutrino mass eigenstate at a time, the model and methods are generalizable to the full 3-flavor case.

We investigate the impact of matter effects on $T$ (time-reversal)-odd observables, making use of the quantum-mechanical formalism of neutrino-flavor evolution. We attempt to be comprehensive and pedagogical. Matter-induced $T$-invariance violation (TV) is qualitatively different from, and more subtle than, matter-induced $CP$ (charge-parity)-invariance violation. If the matter distribution is symmetric relative to the neutrino production and detection points, matter effects will not introduce any new TV. However, if there is intrinsic TV, matter effects can modify the size of the $T$-odd observable. On the other hand, if the matter distribution is not symmetric, there is genuine matter-induced TV. For Earth-bound long-baseline oscillation experiments, these effects are small. This remains true for unrealistically-asymmetric matter potentials (for example, we investigate the effects of “hollowing out” 50% of the DUNE neutrino trajectory). More broadly, we explore consequences, or lack thereof, of asymmetric matter potentials on oscillation probabilities. While fascinating in their own right, $T$-odd observables are currently of limited practical use, due in no small part to a dearth of intense, well-characterized, high-energy electron-neutrino beams. Further in the future, however, intense, high-energy muon storage rings might become available and allow for realistic studies of $T$-invariance in neutrino oscillations.

Boosted dark matter constitutes a small fraction of the total dark matter in the Universe, with mass ranging from eV to MeV and often exhibiting (semi)relativistic velocity. Hence the likelihood of detecting boosted dark matter in Earth-based direct detection experiments is relatively high. There is more than one explanation for the origin of the boosted dark matter including the two-component dark matter models where the heavier dark matter species(dominant) annihilates to nearly monoenergetic light dark matter particles (subdominant) in the galactic halo. If the dominant dark matter species is heavier (MeV-GeV), the subdominant light dark matter achieves (semi)relativistic velocity or boost. These boosted dark matter particles suffer from scattering with electrons and nuclei while crossing the atmosphere and the Earth’s crust before reaching underground experiments and hence the kinetic energy of the dark matter is attenuated. In the two-component dark matter framework, we examine how the boost of the dark matter influences the attenuation of kinetic energy across a broad spectrum of dark matter masses. We perform a detailed study at various DM-electron and DM-nucleus cross sections including the effect of nuclear form factor and elastic and inelastic scattering (for large kinetic energy). For a 10 MeV boosted dark matter with boost $\sim 10-100$, the effect of DM-electron scattering is found to be severe than the DM-nucleus scattering (with form factor) if DM-nucleon scattering cross section is ${10}^{-29}{\mathrm{cm}}^2$. We also show how the peak position of the boosted dark matter flux shifts due to the attenuation of its kinetic energy.

A Wino-like neutralino dark matter (DM) in the form of the lightest supersymmetric particle has been considered one of the popular paradigms that can naturally accommodate new physics at a relatively higher scale, typically beyond the reach of the LHC. The constraint on the DM relic density typically implies a lightest neutralino mass $\simeq 2\mathrm{TeV}$. Its observational signature through nuclear recoil experiments, specifically involving DM-nucleon spin-independent scattering, is not impressive, following its high masses and tiny Higgsino fractions. The theoretical calculations can be improved when we compute all the one-loop electroweak (EW) corrections to the three-point vertices for the neutralino (Wino)-Higgs interactions, which in turn boosts the DM-nucleon scattering cross sections through the standard model-like Higgs exchange. Importantly, we include the counterterm contributions. In addition, we incorporate the other next-to-leading order EW DM-quark and DM-gluon interactions present in the literature to calculate the DM-nucleon scattering cross sections. With the improved and precise theoretical estimates, DM-nucleon scattering cross sections may increase or decrease significantly by more than 100% compared to leading order cross sections in different parts of the parameter space.

We present quantitative results for masses and the internal structure of four-quark states with two heavy quarks, i.e., $Q{Q}^{\prime }\overline{q}{\overline{q}}^{\prime }$ with $Q,Q^{\prime }\in \{c,b\}$ and $q,q^{\prime }\in \{u,d,s\}$, and $J^P\in 1^{+}$. The composition of these states in terms of meson-meson and diquark-antidiquark pairs, extracted from a relativistic four-body Faddeev-Yakubowski equation, is dynamically determined from underlying QCD forces. We find states at energy levels in very good agreement with lattice QCD and, where available, with experimental states. Their internal structure, most notably between the $T_{cc}^{+}$, $T_{bc}$ and $T_{bb}^{-}$, show significant and sizeable variations.

Resonances are ubiquitous phenomena in nature, and physicists have developed many methods to explore resonant states. Of particular note is the complex-momentum-representation (CMR) method, which has been developed and widely used in the study of resonant states in atomic, molecular, and nuclear physics. Here, for the first time, we have developed this novel method to study hadron resonant states. The CMR method is applied to probe the bound and resonant states for the ${\mathrm{\Lambda }}_{c}D(\overline{D})$ and ${\mathrm{\Lambda }}_c{\mathrm{\Lambda }}_c({\overline{\mathrm{\Lambda }}}_c)$ systems, in which the resonant states are exposed clearly in the complex momentum plane and the resonance parameters can be determined precisely without imposing unphysical parameters. The results show that the CMR method has achieved higher accuracy than other widely used methods. This method is not only very effective for narrow resonances, but also can be reliably applied to broad resonances.

The tensor-polarized structures of the deuteron can be probed through the proton-deuteron Drell-Yan process, where the proton is unpolarized and the deuteron is tensor polarized. This measurement will be conducted at Fermilab in the near future. In this reaction, the twist-3 contribution is not negligible compared to the twist-2 contribution due to the limited invariant mass of the dilepton pair. We calculate the twist-3 contribution for the Drell-Yan cross section with a tensor-polarized deuteron target, preserving the U(1)-gauge invariance of the hadronic tensor. The cross sections and weighted cross sections are expressed in terms of the tensor-polarized parton distribution functions (PDFs); thus, one can extract the PDFs $f_{1LL}$, $f_{LT}$, and $f_{1LT}^{(1)}$ from the experimental measurements of Drell-Yan process. Our study should be helpful to solve the puzzle in the tensor-polarized structures of the deuteron.

Exploiting the first measurements of the same ion species in OO collisions at the Relativistic Heavy Ion Collider (RHIC) and LHC, we propose an observable to distinguish whether collective behavior builds up through a hydrodynamic expansion of a strongly interacting quark-gluon plasma or few final state rescatterings. Our procedure allows one to disentangle the effects of the initial state geometry and the dynamical response mechanism on anisotropic flow. We validate its ability to discriminate between systems with different interaction rates using results from event-by-event simulations in kinetic theory.

High-energy nuclear collisions exhibit collective flow, which emerges as a dynamical response of the quark-gluon plasma (QGP) to the initial state geometry of the collision. Collective flow in heavy-ion collisions is usually described within multistage evolution models, which employ a viscous relativistic hydrodynamic description of the space-time evolution of the QGP. By comparing event-by-event simulations in kinetic theory and viscous hydrodynamics in OO, AuAu and PbPb collisions at energies of the Relativistic Heavy Ion Collider (RHIC) and of LHC, we quantify to what extent a macroscopic hydrodynamic description can accurately describe the development of collective flow and to what extent collective flow in small systems, such as OO, is sensitive to the nonequilibrium evolution of the QGP beyond hydrodynamics.