Boltzmann solvers are an important tool for the computation of cosmological observables in the linear regime. In the presence of massive neutrinos, they involve solving the Boltzmann equation followed by an integration in momentum space to arrive at the desired fluid properties, a procedure which is known to be computationally slow. In this work we introduce the so-called generalized Boltzmann hierarchy (GBH) for massive neutrinos in cosmology, an alternative to the usual Boltzmann hierarchy, where the momentum dependence is integrated out leaving us with a two-parameter infinite set of ordinary differential equations. Along with the usual expansion in multipoles, there is now also an expansion in higher velocity weight integrals of the distribution function. Using a toy code, we show that the GBH produces the density contrast neutrino transfer function to a $\lesssim 0.5\%$ accuracy at both large and intermediate scales compared to the neutrino free-streaming scale, thus providing a proof-of-principle for the GBH. We comment on the implementation of the GBH in a state of the art Boltzmann solver.

At second order, scalar perturbations can source traceless and transverse perturbations to the metric, called induced gravitational waves (IGWs). The apparent gauge dependence of the IGWs obscures the interpretation of the stochastic gravitational wave signal. To elucidate the gauge dependence, we study the IGWs from manifestly gauge-invariant scalar perturbations—namely, the relative velocity between baryons and cold dark matter. From this relative velocity perturbation, we compute the dimensionless gravitational wave power spectrum and the corresponding expected angular power spectrum of the $B$-mode polarization of the cosmic microwave background. Although the effect turns out to be unobservably small, the calculation demonstrates both the importance of using observable quantities to remove the gauge ambiguity and the observable consequences of tensor perturbations which are not propagating gravitational waves.

We propose a new model of early dark energy (EDE) as a possible solution to the Hubble tension in cosmology, the apparent discrepancy between local measurements of the Hubble constant $H_0\simeq 74\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ and $H_0\simeq 67\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ inferred from the cosmic microwave background (CMB). In chain EDE, the universe undergoes a series of first order phase transitions, starting at a high energy vacuum in a potential, and tunneling down through a chain of every lower energy metastable minima. As in all EDE models, the contribution of the vacuum energy to the total energy density of the universe is initially negligible, but reaches $\sim 10\%$ around matter-radiation equality, before cosmological data require it to redshift away quickly—at least as fast as radiation. We indeed obtain this required behavior with a series of $N$ tunneling events, and show that for $N>600$ the phase transitions are rapid enough to allow fast percolation and thereby avoid large scale anisotropies in the CMB. We construct a specific example of chain EDE featuring a scalar field in a quasiperiodic potential (a tilted cosine), which is ubiquitous in axion physics and, therefore, carries strong theoretical motivation. Interestingly, the energy difference between vacua can be roughly the size of today’s dark energy (milli-electron-volt scale). Therefore, the end result of chain EDE could provide a natural explanation of dark energy, if the tunneling becomes extremely slow in the final step before the field reaches zero (or negative) energy. We discuss a simple mechanism which can stop the scalar field in the desired minimum. Thus chain EDE offers the exciting prospect to explain EDE and dark energy by the same scalar field.

We introduce a modification of the pysiultralight code that models the dynamical evolution of ultralight axionlike scalar dark matter fields. Our modified code, pysiultralight, adds a quartic, self-interaction term to reflect the one which arises naturally in axionlike particle models. Using a particle mass of ${10}^{-22}\mathrm{eV}/{\mathrm{c}}^2$, we show that pysiultralight produces spatially oscillating solitons, exploding solitons, and collapsing solitons which prior analytic work shows will occur with attractive self-interactions. Using our code we calculate the oscillation frequency as a function of soliton mass and equilibrium radius in the presence of attractive self-interactions. We show that when the soliton mass is below the critical mass ($M_c=\frac{\sqrt{3}}{2}{M}_{\max }$) described by Chavanis [Phys. Rev. D 94, 083007 (2016)] and the initial radius is within a specific range, solitons are unstable and explode. We test the maximum mass criteria described by Chavanis [Phys. Rev. D 94, 083007 (2016)] and Chavanis and Delfini [Phys. Rev. D 84, 043532 (2011)] for a soliton to collapse when attractive self-interactions are included. We also analyze both binary soliton collisions and a soliton rotating around a central mass with attractive and repulsive self-interactions. We find that when attractive self-interactions are included, the density profiles get distorted after a binary collision. We also find that a soliton is less susceptible to tidal stripping when attractive self-interactions are included. We find that the opposite is true for repulsive self-interactions in that solitons would be more easily tidally stripped. Including self-interactions might therefore influence the survival timescales of infalling solitons.

In this article we show that in the usual type-I seesaw framework, augmented solely by a neutrino portal interaction, the dark matter (DM) relic density can be created through freeze-in, in a manner fully determined by the seesaw interactions and the DM particle mass. This simple freeze-in scenario, where dark matter is not in a seesaw state, proceeds through slow, seesaw-induced decays of Higgs $W$ and $Z$ bosons. We identify two scenarios, one of which predicts the existence of an observable neutrino line.

We examine the quark-induced Drell-Yan process at next-to-leading power (NLP) in soft-collinear effective theory. Using an approach with no explicit soft or collinear modes, we discuss the factorization of the differential cross section in the small-$q_T$ hierarchy with $q^2\gg q_T^2\gg {\mathrm{\Lambda }}_{\mathrm{QCD}}^2$. We show that the cross section may be written in terms of matrix elements of power-suppressed operators $T_{(i,j)}$, which contribute to $O(q_T^2/q^2)$ coefficients of the usual parton distribution functions. We derive a factorization for this observable at NLP which allows the large logarithms in each of the relevant factors to be resummed. We discuss the cancellation of rapidity divergences and the overlap subtractions required to eliminate double counting at next-to-leading power.

It has recently been shown that two-loop kite-type diagrams can be computed analytically in terms of iterated integrals with algebraic kernels. This result was obtained using a new integral representation for two-loop sunset subgraphs. In this paper, we have developed a similar representation for a three-loop banana integral in $d=2-2ϵ$ dimensions. This answer can be generalized up to any given order in the $ϵ$-expansion and can be calculated numerically both below and above the threshold. We also demonstrate how this result can be used to compute more complex three-loop integrals containing the three-loop banana as a subgraph.

The XENON collaboration recently reported an excess of electron recoil events in the low energy region with a significance of around $3.3\sigma$. An explanation of this excess in terms of thermal dark matter seems challenging. We propose a scenario where dark matter in the Milky Way halo gets boosted as a result of scattering with the diffuse supernova neutrino background. This interaction can accelerate the dark-matter to semi-relativistic velocities, and this flux, in turn, can scatter with the electrons in the detector, thereby providing a much better fit to the data. We identify regions in the parameter space of dark-matter mass and interaction cross section which satisfy the excess. Furthermore, considering the data only hypothesis, we also impose bounds on the dark-matter scattering cross section, which are competitive with bounds from other experiments.

The quantum Monte Carlo method on asymptotic Lefschetz thimbles is a numerical algorithm devised specifically for alleviation of the sign problem appearing in the simulations of quantum many-body systems. In this method, the sign problem is alleviated by shifting the integration domain for the auxiliary fields, appearing, for example, in the conventional determinant quantum Monte Carlo method, from real space to an appropriate manifold in complex space. Here, we extend this method to quantum spin models with generic two-spin interactions, by using the Hubbard-Stratonovich transformation to decouple the exchange interactions and the Popov-Fedotov transformation to map the quantum spins to complex fermions. As a demonstration, we apply the method to the Kitaev model in a magnetic field whose ground state is predicted to deliver a topological quantum spin liquid with non-Abelian anyonic excitations. To illustrate how the sign problem is alleviated in this method, we visualize the asymptotic Lefschetz thimbles in complex space, together with the saddle points and the zeros of the fermion determinant. We benchmark our method in the low-temperature region in a magnetic field and show that the sign of the action is recovered considerably and unbiased numerical results are obtained with sufficient precision.

The $CP$-violating quark chromoelectric dipole moment (qCEDM) operator, contributing to the electric dipole moment (EDM), mixes under renormalization and—particularly on the lattice—with the pseudoscalar density. The mixing coefficient is power-divergent with the inverse lattice spacing squared, $1/a^2$, regardless of the lattice action used. We use the gradient flow to define a multiplicatively renormalized qCEDM operator and study its behavior at small flow time. We determine nonperturbatively the linearly divergent coefficient with the flow time, $1/t$, up to subleading logarithmic corrections, and compare it with the 1-loop perturbative expansion in the bare and renormalized strong coupling. We also discuss the $\mathrm{O}(a)$ improvement of the qCEDM defined at positive flow time.

We investigate the properties of neutral and charged pions in a constant background magnetic field mainly at zero temperature within the Nambu–Jona-Lasinio model. In the previous calculations, the Ritus method involving Schwinger phases in a fixed gauge was employed within the momentum-space random phase approximation (RPA) [M. Coppola et al., Phys. Lett. B 782, 155 (2018).]. However, gauge invariance of the charged pion masses has not yet been examined. In this work, by adopting the linear response theory based on the imaginary-time path integral formalism, we derive the correlation functions for pions in coordinate space, where the corresponding Schwinger phases show up automatically. At sufficiently large imaginary time $\tau$, the meson correlation function approaches an exponential form $\sim \exp (-E_{\mathrm{G}}\tau )$, where $E_{\mathrm{G}}$ is the ground-state energy of the one-meson state and hence determined as the meson mass. Furthermore, we show that the mass of the charged pions is gauge independent, i.e., independent of the choice of the vector potential for the magnetic field. Actually, we also find that the momentum-space RPA is equivalent to the imaginary-time method used here.

Propagators of confined particles, especially the Landau-gauge gluon propagator, may have complex singularities as suggested by recent numerical works as well as several theoretical models, e.g., motivated by the Gribov problem. In this paper, we study formal aspects of propagators with complex singularities in reconstructing Minkowski propagators starting from Euclidean propagators by the analytic continuation. We derive the following properties rigorously for propagators with arbitrary complex singularities satisfying some boundedness condition. The two-point Schwinger function with complex singularities violates the reflection positivity. In the presence of complex singularities, while the holomorphy in the usual tube is maintained, the reconstructed Wightman function on the Minkowski spacetime becomes a nontempered distribution and violates the positivity condition. On the other hand, the Lorentz symmetry and locality are kept intact under this reconstruction. Finally, we argue that complex singularities can be realized in a state space with an indefinite metric and correspond to confined states. We also discuss consequences of complex singularities in the Becchi-Rouet-Stora-Tyutin formalism. Our results could open up a new way of understanding a confinement mechanism, mainly in the Landau-gauge Yang-Mills theory.

The photoproduction of large $p_T$ dileptons, photons, and light vector mesons in $p\text{−}p$, $p\text{−}\mathrm{Pb}$, and $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions at LHC energies is studied, where the fragmentation processes and the ultra-incoherent photon channel are included. An exact treatment is developed for photoproduction processes in heavy ion collisions, which recovers the equivalent photon approximation (EPA) in the limit $Q^2\to 0$ and can avoid double counting effectively. The full kinematical relations are also achieved. We present the results as the distributions in $Q^2$, $p_T$, and $y_r$, and the total cross sections are also estimated. The numerical results indicate that the contribution of photoproduction processes is evident in the large $p_T$ and $y_r$ regions and starts to play a fundamental role in $p\text{−}\mathrm{Pb}$ collisions. The ultra-incoherent photon emission is an important channel of photoproduction processes, which can provide the meaningful contributions. EPA is only applicable in small $y$ and $Q^2$ domains and is very sensitive to the values of $y_{\max }$ and $Q_{\max }^2$. The EPA errors appear when $y>0.29$ and $Q^2>0.1{\mathrm{GeV}}^2$ and are rather serious in $p\text{−}\mathrm{Pb}$ and $\mathrm{Pb}\text{−}\mathrm{Pb}$ collisions. When dealing with widely kinematical regions, the exact treatment needs to be adopted.

The three pentaquark states, $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$, discovered by the LHCb Collaboration in 2019, can be nicely arranged into a multiplet of ${\overline{D}}^{(*)}{\mathrm{\Sigma }}_c^{(*)}$ of seven molecules dictated by heavy quark spin symmetry. In this work we employ the effective Lagrangian approach to investigate the two decay modes of $P_c(4457)$, $P_c(4457)\to P_c(4312)\pi$, and $P_c(4457)\to P_c(4312)\gamma$, via the triangle mechanism, assuming that $P_c(4457)$ and $P_c(4312)$ are ${\overline{D}}^{*}{\mathrm{\Sigma }}_c$ and $\overline{D}{\mathrm{\Sigma }}_c$ bound states but the spin of $P_c(4457)$ can be either $1/2$ or $3/2$. Our results show that the spin of $P_c(4457)$ can not be discriminated through these two decay modes. The decay widths of $P_c(4457)\to P_c(4312)\pi$ and $P_c(4457)\to P_c(4312)\gamma$ are estimated to be of order of 100 keV and 1 keV, respectively. The ratio of the partial decay widths of $P_c(4457)\to P_c(4312)\pi$ to $P_c(4457)\to P_c(4312)\gamma$ is similar to the ratio of $D^{*}\to D\pi$ to $D^{*}\to D\gamma$, which could be used to check the molecular nature of $P_c(4457)$ and $P_c(4312)$ if they can be observed in the future.

We summarize the results of a study performed within the GENIE global analysis framework, revisiting the GENIE bare-nucleon cross-section tuning and, in particular, the tuning of (a) the inclusive cross section, (b) the cross section of low-multiplicity inelastic channels (single-pion and double-pion production), and (c) the relative contributions of resonance and nonresonance processes to these final states. The same analysis was performed with several different comprehensive cross-section model sets available in GENIE Generator v3. In this work we perform a careful investigation of the observed tensions between exclusive and inclusive data, and install analysis improvements to handle systematics in historic data. All tuned model configurations discussed in this paper are available through public releases of the GENIE Generator. With this paper we aim to support the consumers of these physics tunes by providing comprehensive summaries of our alternate model constructions, of the relevant datasets and their systematics, and of our tuning procedure and results.

The goal of this short note is to provide a simpler derivation of the effective potential surrounding a Schwarzschild black hole for spherically symmetric perturbations in the framework of torsion bigravity than the one presented in [V. Nikiforova, Spherically symmetric perturbations of a Schwarzschild black hole in torsion bigravity, Phys. Rev. D 104, 024032 (2021).]. We also discuss the unicity of the reduction process that leads to the potential.

We perform canonical quantization of gravity in the background of a Schwarzschild black hole in the generalized Regge-Wheeler gauge proposed in Kallosh and Rahman [Quantization of gravity in the black hole background, Phys. Rev. D 104, 086008 (2021)]. We find that the Hamiltonian at the quadratic level is unitary and ghost-free. Two canonical degrees of freedom are associated with Zerilli-Moncrief and Cunningham-Price-Moncrief functions of the metric perturbations. The $\ell <2$ part of the Hamiltonian vanishes. This quantization with the unitary Hamiltonian for gravity is valid also in Minkowski space in spherical coordinates.

The exact one-loop beta functions for the four-derivative terms (Weyl tensor squared, Ricci scalar squared, and the Gauss-Bonnet) are derived for the minimal six-derivative quantum gravity (QG) theory in four spacetime dimensions. The calculation is performed by means of the Barvinsky and Vilkovisky generalized Schwinger-DeWitt technique. With this result we gain, for the first time, the full set of the relevant beta functions in a super-renormalizable model of QG. The complete set of renormalization group (RG) equations, including also those for the Newton and the cosmological constant, is solved explicitly in the general case and for the six-derivative Lee-Wick (LW) quantum gravity proposed in a previous paper by two of the authors. In the ultraviolet regime, the minimal theory is shown to be asymptotically free and describes free gravitons in Minkowski or (anti–)de Sitter [(A)dS] backgrounds, depending on the initial conditions for the RG equations. The ghostlike states appear in complex conjugate pairs at any energy scale consistently with the LW prescription. However, owing to the running, these ghosts may become tachyons. We argue that an extension of the theory that involves operators cubic in Riemann tensor may change the beta functions and hence be capable of overcoming this problem.

We provide an exhaustive analysis of the complete set of solutions of the equations of stellar equilibrium under semiclassical effects. As classical matter we use a perfect fluid of constant density; as the semiclassical source we use the renormalized stress-energy tensor (RSET) of a minimally coupled massless scalar field in the Boulware vacuum (the only vacuum consistent with asymptotic flatness and staticity). For the RSET we use a regularized version of the Polyakov approximation. We present a complete catalogue of the semiclassical self-consistent solutions which incorporates regular as well as singular solutions, showing that the semiclassical corrections are highly relevant in scenarios of high compactness. Semiclassical corrections allow the existence of ultracompact equilibrium configurations which have bounded pressures and masses up to a central core of Planckian radius, precisely where the regularized Polyakov approximation is not accurate. Our analysis strongly suggests the absence of a Buchdahl limit in semiclasical gravity, while indicating that the regularized Polyakov approximation used here must be improved to describe equilibrium configurations of arbitrary compactness that remain regular at the center of spherical symmetry.

Modified Newtonian dynamics by Milgrom is a paradigm for explaining the rotation curves of spiral galaxies and various other large scale structures. This paradigm includes several different theories. Here we present Milgrom’s modifed inertia (MI) theory in terms of a simple and tractable nonconservative Newtonian dynamics, which is useful in obtaining observable predictions of MI. It is found that: 1) Modified inertia theory is equivalent to a Newtonian theory, with a nonconservative gravitational field, and dark matter density; 2) The tidal force in the equivalent Newtonian dynamics is nonconservative, and its effect on a binary system in free fall in the gravitational field of a spheroid is addressed. We also discuss attempts to restore conservations in MI.