A measurement of the neutrino mass scale will be achieved with cosmological probes in the upcoming decade. On one hand, the inclusion of massive neutrinos in the linear perturbation theory of cosmological structure formation is well understood and can be done accurately with state of the art Boltzmann solvers. On the other hand, the numerical implementation of the Boltzmann equation is computationally expensive and is a bottleneck in those codes. This has motivated the development of more efficient fluid approximations, despite their limited accuracy over all scales of interest, $k\sim ({10}^{-3}-10){\mathrm{Mpc}}^{-1}$. In this work we account for the dispersive nature of the neutrino fluid, i.e., the scale dependence in the sound speed, leading to an improved fluid approximation. We show that overall $\lesssim 5\%$ errors can be achieved for the neutrino density and velocity transfer functions at redshift $z\lesssim 5$, which corresponds to an order of magnitude improvement over previous approximation schemes that can be discrepant by as much as a factor of two.

Based on a formalism introduced in our previous work, we reconstruct the phenomenological function $G_{\mathrm{eff}}(z)$ describing deviations from general relativity (GR) in a model-independent manner. In this alternative approach, we model $\mu \equiv G_{\mathrm{eff}}/G$ as a Gaussian process and use forecasted growth-rate measurements from a stage-IV survey to reconstruct its shape for two different toy-models. We follow a two-step procedure: (i) we first reconstruct the background expansion history from supernovae (SNe) and baryon acoustic oscillation (BAO) measurements; (ii) we then use it to obtain the growth history $f{\sigma }_8$, that we fit to redshift-space distortions (RSD) measurements to reconstruct $G_{\mathrm{eff}}$. We find that upcoming surveys such as the dark energy spectroscopic instrument (DESI) might be capable of detecting deviations from GR, provided the dark energy behavior is accurately determined. We might even be able to constrain the transition redshift from $G\to G_{\mathrm{eff}}$ for some particular models. We further assess the impact of massive neutrinos on the reconstructions of $G_{\mathrm{eff}}$ (or $\mu$) assuming the expansion history is given, and only the neutrino mass is free to vary. Given the tight constraints on the neutrino mass, and for the profiles we considered in this work, we recover numerically that the effect of such massive neutrinos do not alter our conclusions. Finally, we stress that incorrectly assuming a $\mathrm{\Lambda }\mathrm{CDM}$ expansion history leads to a degraded reconstruction of $\mu$, and/or a non-negligible bias in the $({\mathrm{\Omega }}_{\mathrm{m},0},{\sigma }_{8,0})$-plane.

Studying the properties of ultradense matter is one of the key goals of modern neutron star research. The measurement of the tidal deformability from the inspiral of a binary neutron star merger offers one promising method for constraining the equation of state (EoS) of cold, dense matter. In this work, we report on a new class of EoSs which have significantly different pressures at nuclear densities and large differences in stellar radii, but that predict surprisingly similar tidal deformabilities across the entire range of astrophysically-observed neutron star masses. Using a survey of 5 million piecewise polytropic EoSs, subject to five different sets of nuclear priors, we demonstrate that these “tidal deformability doppelgängers” occur generically. We find that they can differ substantially in the pressure (by up to a factor of 3 at nuclear densities) and in the radius of intermediate-mass neutron stars (by up to 0.5 km), but are observationally indistinguishable in their tidal deformabilities ($\mathrm{\Delta }\mathrm{\Lambda }\lesssim 30$) with the sensitivity of current gravitational wave detectors. We demonstrate that this near-degeneracy in the tidal deformability is a result of allowing for a phase transition at low densities. We show that a combination of input from nuclear theory (e.g., from chiral effective field theory), x-ray observations of neutron star radii, and/or the next generation of gravitational wave detectors will be able to significantly constrain these tidal deformability doppelgängers.

A major challenge of particle physics is determining the neutrino mass ordering (MO). Due to matter effects, the flavor content of the neutrino flux from a core-collapse supernova (CCSN) depends on the true neutrino MO resulting in markedly different energy and angle distributions for the measured lepton in water Cherenkov neutrino detectors. In this article, those distributions are compared for eight different CCSN models and used to study how their differences affect the determination of the neutrino mass ordering. In all cases, the inferred neutrino mass ordering is found to be either correct or inconclusive, with no significant false positives. However, the substantial variation observed among model predictions emphasizes the criticality of ongoing research in CCSN modeling.

The Indian Pulsar Timing Array (InPTA) collaboration has recently made its first official data release (DR1) for a sample of 14 pulsars using 3.5 years of uGMRT observations. We present the results of single-pulsar noise analysis for each of these 14 pulsars using the InPTA DR1. For this purpose, we consider white noise, achromatic red noise, dispersion measure (DM) variations, and scattering variations in our analysis. We apply Bayesian model selection to obtain the preferred noise models among these for each pulsar. For PSR $\mathrm{J}1600-3053$, we find no evidence of DM and scattering variations, while for PSR $\mathrm{J}1909-3744$, we find no significant scattering variations. Properties vary dramatically among pulsars. For example, we find a strong chromatic noise with chromatic index $\sim 2.9$ for PSR $\mathrm{J}1939+2134$, indicating the possibility of a scattering index that does not agree with that expected for a Kolmogorov scattering medium consistent with similar results for millisecond pulsars in past studies. Despite the relatively short time baseline, the noise models broadly agree with the other PTAs and provide, at the same time, well-constrained DM and scattering variations.

LIGO’s mission critical timing system has enabled gravitational wave and multimessenger astrophysical discoveries as well as the rich science extracted. Achieving optimal detector sensitivity, detecting transient gravitational waves, and especially localizing gravitational wave sources, the underpinning of multimessenger astrophysics, all require proper gravitational wave data time stamping. Measurements of the relative arrival times of gravitational waves between different detectors allow for coherent gravitational wave detections, localization of gravitational wave sources, and the creation of sky maps. The carefully designed timing system achieves these goals by mitigating phase noise to avoid signal up-conversion and maximize gravitational wave detector sensitivity. The timing system also redundantly performs self-calibration and self-diagnostics in order to ensure reliable, extendable, and traceable time stamping. In this paper, we describe and quantify the performance of these core systems during the latest O3 scientific run of LIGO, Virgo, and KAGRA. We present results of the diagnostic checks done to verify the time stamping for individual gravitational wave events observed during O3 as well as the timing system performance for all of O3 in LIGO Livingston and LIGO Hanford. We find that, after three observing runs, the LIGO timing system continues to reliably meet mission requirements of timing precision below $1\mathrm{\mu }\mathrm{s}$ with a significant safety margin.

We introduce a new jet clustering algorithm named SIFT (scale-invariant filtered tree) that maintains the resolution of substructure for collimated decay products at large boosts. The scale-invariant measure combines properties of $k_{\mathrm{T}}$ and anti-$k_{\mathrm{T}}$ by preferring the early association of soft radiation with a resilient hard axis, while avoiding the specification of a fixed cone size. Integrated filtering and variable-radius isolation criteria block assimilation of soft wide-angle radiation and provide a halting condition. Mutually hard structures are preserved to the end of clustering, automatically generating a tree of subjet axis candidates. Excellent object identification and kinematic reconstruction for multipronged resonances are realized across more than an order of magnitude in transverse energy. The clustering measure history facilitates high-performance substructure tagging, which we quantify with the aid of supervised machine learning. These properties suggest that SIFT may prove to be a useful tool for the continuing study of jet substructure.

The explicit compact expression for the susceptibility tensor of a single photon wave packet on the photon mass-shell is derived. It is assumed that the probe photon is hard, the tested photon is soft, and their total energy is below the electron-positron pair creation threshold. It turns out that a single photon wave packet can be regarded as a birefringent gyrotropic dispersive medium in the process of light-by-light scattering. The explicit expression for the inclusive probability to record the probe photon in the process of light-by-light scattering is obtained in the first nontrivial order of perturbation theory where the interference effect of the free passed and scattered parts of the photon wave function dominates. This effect is of order ${\alpha }^2$ in contrast to the standard contribution to the light-by-light scattering cross section which is of order ${\alpha }^4$. The possible nontrivial shapes of the wave functions of probe and tested photons are taken into account. The evolution of the Stokes parameters of a probe photon is described. The change of the Stokes parameters is rather large for hard probe photons and sufficiently intense beams of soft tested photons.

We investigate the preservation of unitarity in a Lorentz and $CPT$-violating QED model containing higher-order operators. In particular, we consider modifications in the fermion sector with dimension-five operators. The higher-order operators lead to an indefinite metric and a pseudo-unitarity relation for the $S$-matrix. However, we show that the pseudo-unitarity condition can be promoted to a genuine unitarity relation by (i) restricting the energies to the effective region far below the Planck mass and (ii) considering stable particles to have a positive metric. In the context of the optical theorem, we focus on the one-loop Bhabha and Compton scattering processes. We show that no ghost states get propagated through the cuts, thus satisfying the unitarity condition. Further, we show that discontinuities of propagators are equivalent to replacing physical Dirac functionals in the cutting equation. The physical Dirac functionals are defined to select only mode solutions of stable particles. The provided extension of the Cutkosky rule may be helpful for analyzing perturbative unitarity in higher-order diagrams.

The SuperKamiokande experiment tightly bounds the lifetimes of the baryon number-violating proton decays. The decay widths for the nucleon to an antilepton and a photon are not so well-bounded experimentally as $\ell \pi$ modes. Using an effective Lagrangian approach, we relate the decay widths of $N\to \ell \gamma$ to the decay widths of $N\to \ell \pi$. Our result points out a factor of ${10}^3$ suppression of the decay widths $\mathrm{\Gamma }(p\to {\ell }^{+}\gamma )$ and $\mathrm{\Gamma }(n\to \overline{\nu }\gamma )$ compared to the decay widths $\mathrm{\Gamma }(p\to {\ell }^{+}{\pi }^0)$ and $\mathrm{\Gamma }(n\to \overline{\nu }{\pi }^0)$, respectively. This result is independent of the model of new physics. Then, we investigate the dynamics of $N\to \ell \pi$ and $N\to \ell \gamma$ amplitudes at the tree and loop level in which scalar leptoquarks are mediators of a new interaction. At the tree level, leptoquarks probe the physics beyond the Standard Model at a scale of ${10}^{16}\mathrm{GeV}$, while at the loop level, such decay can occur at a scale of ${10}^7\mathrm{GeV}$.

We formulate a light-front spectator model for the proton incorporating the gluonic degree of freedom. In this model, at high energy scattering of the proton, the active parton is a gluon and the rest is viewed as a spin-$\frac{1}{2}$ spectator with an effective mass. The light front wave functions of the proton are constructed using a soft wall AdS/QCD prediction and parametrized by fitting the unpolarized gluon distribution function to the NNPDF3.0nlo dataset. We investigate the helicity distribution of gluon in this model. We find that our prediction for the gluon helicity asymmetry agrees well with existing experimental data and satisfies the perturbative QCD constraints at small and large longitudinal momentum regions. We also present the transverse momentum dependent distributions (TMDs) for gluon in this model. We further show that the model-independent Mulders-Rodrigues inequalities are obeyed by the TMDs computed in our model.

We study, to all orders in perturbative QCD, the universal behavior of the saturation momentum $Q_s(L)$ controlling the transverse momentum distribution of a fast parton propagating through a dense QCD medium with large size $L$. Due to the double logarithmic nature of the quantum evolution of the saturation momentum, its large $L$ asymptotics is obtained by slightly departing from the double logarithmic limit of either next-to-leading log (NLL) BFKL or leading order DGLAP evolution equations. At fixed coupling, or in conformal $\mathcal{N}=4$ SYM theory, we derive the large $L$ expansion of $Q_s(L)$ up to order ${\alpha }_s^{3/2}$. In QCD with massless quarks, where conformal symmetry is broken by the running of the strong coupling constant, the 1-loop QCD $\beta$-function fully accounts for the universal terms in the $Q_s(L)$ expansion. Therefore, the universal coefficients of this series are known exactly to all orders in ${\alpha }_s$.

The LHCb experiment has recently reported two excited ${\mathrm{\Omega }}_c$ resonances decaying to ${\mathrm{\Xi }}_c^{+}{K}^{-}$, with masses about 3185 MeV and 3327 MeV. We discuss their assignment to $2S_{1/2}$ and $2S_{3/2}$ states, which can be compared with masses based on extrapolation from the observed $1S$ states. The agreement is not perfect, but weighs against an earlier alternative assignment. Consequences for the spin-averaged $2P$ states are discussed.

We report the first measurement of the $Q^2$ distribution of $X(3915)$ produced by single-tag two-photon interactions. The decay mode used is $X(3915)\to J/\psi \omega$. The covered $Q^2$ region is from $1.5(\mathrm{GeV}/c{)}^2$ to $10.0(\mathrm{GeV}/c{)}^2$. We observe $7.9\pm 3.1(\mathrm{stat})\pm 1.5(\mathrm{syst})$ events, where we expect $4.1\pm 0.7$ events based on the $Q^2=0$ result from the no-tag two-photon process, extrapolated to higher $Q^2$ region using the $c\overline{c}$ model of Schuler, Berends, and van Gulik. The shape of the distribution is also consistent with this model; we note that statistical uncertainties are large.

We present the first measurement of the Michel parameter ${\xi }^{\prime }$ in the ${\tau }^{-}\to {\mu }^{-}{\overline{\nu }}_{\mu }{\nu }_{\tau }$ decay using the full data sample of $988{\mathrm{fb}}^{-1}$ collected by the Belle detector operating at the KEKB asymmetric energy $e^{+}{e}^{-}$ collider. The method is based on the reconstruction of the ${\mu }^{-}\to e^{-}{\overline{\nu }}_e{\nu }_{\mu }$ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We study the main sources of the background that can imitate the signal decay, such as kaon and pion decays-in-flight and charged particle scattering on the detector material. Highly efficient methods of their suppression are developed and applied to select 165 signal-candidate events. We obtain ${\xi }^{\prime }=0.22\pm 0.94\pm 0.42$ where the first uncertainty is statistical, and the second one is systematic. The result is in agreement with the Standard Model prediction of ${\xi }^{\prime }=1$.

It has been recently pointed out that nonlinear effects are necessary to model the ringdown stage of the gravitational waveform produced by the merger of two black holes giving rise to a remnant Kerr black hole. We show that this nonlinear behavior is explained, both on the qualitative and quantitative level, by near-horizon symmetries of the Kerr black hole within the Kerr/CFT correspondence.

In the framework of the static patch approach to de Sitter holography introduced in [L. Susskind, J. Hologr. Appl. Phys. 1, 1 (2021)], the growth of holographic complexity has a hyperfast behavior, which leads to a divergence in a finite time. This is very different from the anti–de Sitter (AdS) spacetime, where instead the complexity rate asymptotically reaches a constant value. We study holographic volume complexity in a class of asymptotically AdS geometries which include de Sitter bubbles in their interior. With the exception of the static bubble case, the complexity obtained from the volume of the smooth extremal surfaces which are anchored just to the AdS boundary has a similar behavior to the AdS case, because it asymptotically grows linearly with time. The static bubble configuration has a zero complexity rate and corresponds to a discontinuous behavior, which resembles a first order phase transition. If instead we consider extremal surfaces which are anchored at both the AdS boundary and the de Sitter stretched horizon, we find that complexity growth is hyperfast, as in the de Sitter case.

We investigate two types of excited oscillons. We first focus on spherical symmetry and find that there are a tower of spherical oscillons with higher energies. Despite having multiple approximate “nodes” in their energy density profiles, these oscillons are long-lived. We find that during the lifetime of an excited oscillon it will cascade down all of the lower energy levels before its disintegration, with each level-dropping period accompanied by a short burst of energy. We also point out the existence of excited oscillons with higher approximate multipoles, which generally have shorter lifespans than the spherical ones. Apart from performing nonlinear simulations with absorbing boundary conditions, we also apply a perturbative method to analyze some features of these excited oscillons.