We consider the cosmological production of fermionic dark matter during inflation and a postinflationary radiation dominated era. This fermion only interacts gravitationally, has a mass $m$ much smaller than the Hubble scale during inflation (but is otherwise arbitrary), and is in its Bunch-Davies vacuum state during inflation. We focus on superhorizon modes at the end of inflation and assume instantaneous reheating. We obtain the full energy momentum tensor discussing its renormalization and show that the contribution from particle production is of the kinetic-fluid form near matter-radiation equality. We find exactly the distribution function of produced particles $|B(k){|}^2=\frac{1}{2}[1-(1-e^{-\frac{k^2}{2m{T}_H}}{)}^{1/2}]$, which exhibits an “emergent temperature” $T_H=H_0\sqrt{{\mathrm{\Omega }}_R}\simeq {10}^{-36}(\mathrm{eV})$. The energy density of produced particles ${\rho }_{pp}$ is very similar to that of a nonrelativistic degree of freedom thermalized at temperature $T_H$, ${\rho }_{pp}\propto m(m{T}_H{)}^{3/2}/a^3$ with abundance ${\mathrm{\Omega }}_{pp}\simeq (m/{10}^8\mathrm{GeV}{)}^{5/2}$ and “cold” equation of state $w(a)\simeq (T_H/m{a}^2)$, both dominated by superhorizon modes at the end of inflation. We discuss subtle aspects of isocurvature perturbations.

Based on tensions between the early and late time cosmology, we proposed a double valued cosmological constant which could undergo a phase transition in its history. It is named “double-$\mathrm{\Lambda }$ Cold Dark Matter”: $\mathrm{\Lambda }\mathrm{\Lambda }\mathrm{CDM}$. The phase transition occurred because of (micro-) structures for the dark sector with a proper (local) interaction. In this paper, inspired by the physics of critical phenomena, we study a simplified model such that the cosmological constant has two values before a transition scale factor, $a_t$, and afterwards it becomes single valued. We consider both the background and perturbation datasets including cosmic microwave background (CMB), Baryon acoustic oscillations (BAO) distances, and R19 data points. $\mathrm{\Lambda }\mathrm{\Lambda }\mathrm{CDM}$ has its maximum likelihood for $a_t=0.851_{+0.027}^{+0.12}$ and gives $H_0={72.2}_{-1.5}^{+2.2}$. This result shows no inconsistency between early and late time measurements of the Hubble parameter in the $\mathrm{\Lambda }\mathrm{\Lambda }\mathrm{CDM}$ model. In comparison to $\mathrm{\Lambda }\mathrm{CDM}$, our model has better fit to data with $\mathrm{\Delta }{\chi }^2=-16$ and we even have a better Akaike information criterion (AIC) quantity $\mathrm{\Delta }\mathrm{AI}\mathrm{C}=-12$, where our model is penalized because of two more degrees of freedom. We conclude that a phase transition in the behavior of dark energy can address $H_0$ tension successfully and may be responsible for the other cosmological tensions.

We consider the big bang nucleosynthesis (BBN) bounds on light dark matter whose cross section off nucleons is sufficiently large to enable acceleration by scattering off of cosmic rays in the local galaxy. Such accelerated DM could then deposit energy in terrestrial detectors. Since this signal involves DM of mass $\sim \mathrm{keV}-\mathrm{GeV}$ and requires large cross sections $\gtrsim {10}^{-31}{\mathrm{cm}}^2$ in a relativistic kinematic regime, we find that the DM population in this scenario is generically equilibrated with Standard Model particles in the early universe. For sufficiently low DM masses $\lesssim 10\mathrm{MeV}$, corresponding to much of the favored region of many cosmic-ray upscattering studies, this equilibrated DM population adds an additional component to the relativistic energy density around $T\sim \mathrm{few}$ MeV and thereby spoils the successful predictions of BBN. In the remaining $\sim 10\mathrm{MeV}–\mathrm{GeV}$ mass range, the large couplings required in this scenario are either currently excluded or within reach of current or future accelerator-based searches.

Cosmological tensions can arise within the Lamda cold dark matter scenario amongst different observational windows, which may indicate new physics beyond the standard paradigm if confirmed by measurements. In this article, we report how to alleviate both the $H_0$ and ${\sigma }_8$ tensions simultaneously within torsional gravity from the perspective of effective field theory. Following these observations, we construct concrete models of Lagrangians of torsional gravity. Specifically, we consider the parametrization $f(T)=-T-2\mathrm{\Lambda }/M_P^2+\alpha T^{\beta }$, where two out of the three parameters are independent. This model can efficiently fit observations solving the two tensions. To our knowledge, this is the first time where a modified gravity theory can alleviate both $H_0$ and ${\sigma }_8$ tensions simultaneously, hence, offering an additional argument in favor of gravitational modification.

We introduce a dark neutrino sector which respects a hidden $U(1{)}^{\prime }$ gauge symmetry, subsequently broken by the vacuum expectation value of a dark scalar. The model is a self-consistent realization of an extended hidden sector that communicates with the standard model only via the three renormalizable portals, namely, neutrino, vector and scalar mixing. The interplay between portal couplings leads to several novel signatures in heavy neutrino, dark photon, and dark scalar searches, typically characterized by multileptons plus missing energy and displaced vertices. A striking signature arises in kaon factories such as NA62, where $K^{+}\to {\ell }_{\alpha }^{+}\nu {\ell }_{\beta }^{+}{\ell }_{\beta }^{-}$ decays could reveal a heavy neutrino and a light dark photon resonance above backgrounds. Given the open parameter space, we also comment on recent ideas to explain outstanding experimental anomalies, and how they would fit into our proposed model. A minimal extension of the model, possibly motivated by anomaly cancellation, can accommodate a dark matter candidate strongly connected to the neutrino sector.

We describe a scenario where the smallness of neutrino masses is related to a global symmetry that is only violated by quantum gravitational effects. The coupling of neutrinos to gauge singlet right-handed fermions is attributed to symmetry preserving gravitational operators suppressed by the Planck mass, in this framework. The proposed scenario leads to axion particles that decay into neutrinos, which could be probed through cosmological measurements and may help explain the Hubble parameter tension. Depending on the details of the implementation, the scenario could provide axion dark matter candidates.

In quantum chromodynamics (QCD), the role which topologically nontrivial configurations play in splitting the singlet pseudo-Goldstone meson, the ${\eta }^{\prime }$, from the octet is familiar. In addition, such configurations contribute to other processes which violate the axial $U(1{)}_A$ symmetry. While the nature of topological fluctuations in the vacuum is still unsettled, at temperatures above that for the chiral phase transition, they can be described by a dilute gas of instantons. We show that instantons of arbitrary topological charge $Q$ generate anomalous interactions between $2N_f|Q|$ quarks, which for $Q=1$ make the ${\eta }^{\prime }$ heavy. For two flavors we compute an anomalous quartic meson coupling and discuss its implications for the phenomenology of the chiral phase transition. A dilute instanton gas suggests that for cold, dense quarks, instantons do not evaporate until very high densities, when the baryon chemical potential is $\gtrsim 2\mathrm{GeV}$.

Nonperturbative gauge invariance under the strong and the weak interactions dictates that the proton contains a nonvanishing valence contribution from the Higgs particle. By introducing an additional parton distribution function (PDF), we investigate the experimental consequences of this prediction. The herwig7 event generator and a parameterized CMS detector simulation are used to obtain predictions for a scenario amounting to the LHC run-II dataset. We use those to assess the impact of the Higgs PDF on the $pp\to t\overline{t}$ process in the single-lepton final state. Comparing to nominal simulation we derive expected limits as a function of the shape of the valence Higgs PDF. We also investigate the process $pp\to t\overline{t}Z$ at the parton level to add further constraints.

Binary black holes in which both spins are aligned with the binary’s orbital angular momentum do not precess. However, the up-down configuration, in which the spin of the heavier (lighter) black hole is aligned (anti-aligned) with the orbital angular momentum, is unstable to spin precession at small orbital separations [D. Gerosa et al., Phys. Rev. Lett. 115, 141102 (2015)]. We first cast the spin precession problem in terms of a simple harmonic oscillator and provide a cleaner derivation of the instability onset. Surprisingly, we find that following the instability, up-down binaries do not disperse in the available parameter space but evolve toward precise endpoints. We then present an analytic scheme to locate these final configurations and confirm them with numerical integrations. Namely, unstable up-down binaries approach mergers with the two spins coaligned with each other and equally misaligned with the orbital angular momentum. Merging up-down binaries relevant to LIGO/Virgo and LISA may be detected in these endpoint configurations if the instability onset occurs prior to the sensitivity threshold of the detector. As a by-product, we obtain new generic results on binary black hole spin-orbit resonances at 2nd post-Newtonian order. We finally apply these findings to a simple astrophysical population of binary black holes where a formation mechanism aligns the spins without preference for co- or counteralignment, as might be the case for stellar-mass black holes embedded in the accretion disk of a supermassive black hole.

We study the geodesics of charged black holes in polynomial Maxwell Lagrangians, a subclass of models within the nonlinear electrodynamics (NLED). Specifically, we consider black holes in Kruglov, power-law, and Ayon-Beato-Garcia models. Our exploration on the corresponding null bound states reveals that a photon can orbit the extremal black holes in stable radii outside the corresponding horizon, contrary to the case of the Reissner-Nordstrom black holes. The reason behind this is the well-known theorem that a photon in a NLED background propagates along its own effective geometry. This nonlinearity is able to shift the local minimum of the effective potential away from its corresponding outer horizon. For the null scattering states, we obtain corrections to the weak deflection angle off the black holes. We rule out the power-law model to be physical since its deflection angle does not reduce to the Schwarzschild in the limit of the vanishing charge.

We introduce a physically motivated model of the matter power spectrum, based on the halo model and perturbation theory. This model achieves 1% accuracy on all $k$-scales between $k=0.02h{\mathrm{Mpc}}^{-1}$ to $k=1h{\mathrm{Mpc}}^{-1}$. Our key ansatz is that the number density of halos depends on the nonlinear density contrast filtered on some unknown scale $R$. Using the effective field theory of large scale structure to evaluate the two-halo term, we obtain a model for the power spectrum with only two fitting parameters: $R$ and the effective “sound speed,” which encapsulates small-scale physics. This is tested with two suites of cosmological simulations across a broad range of cosmologies and found to be highly accurate. Due to its physical motivation, the statistics can be easily extended beyond the power spectrum; we additionally derive the one-loop covariance matrices of cluster counts and their combination with the matter power spectrum. This yields a significantly better fit to simulations than previous models, and includes a new model for supersample effects, which is rigorously tested with separate universe simulations. At low redshift, we find a significant ($\sim 10\%$) exclusion covariance from accounting for the finite size of halos which has not previously been modeled. Such power spectrum and covariance models will enable joint analysis of upcoming large-scale structure surveys, gravitational lensing surveys, and cosmic microwave background maps on scales down to the nonlinear scale. We provide a publicly released python code.

An old question surrounding bouncing models concerns their stability under vector perturbations. Considering perfect fluids or scalar fields, vector perturbations evolve kinematically as $a^{-2}$, where $a$ is the scale factor. Consequently, a definite answer concerning the bounce stability depends on an arbitrary constant, therefore, there is no definitive answer. In this paper, we consider a more general situation where the primeval material medium is a nonideal fluid, and its shear viscosity is capable of producing torque oscillations, which can create and dynamically sustain vector perturbations along cosmic evolution. In this framework, it can be defined that vector perturbations have a quantum mechanical origin, coming from quantum vacuum fluctuations in the far past of the bouncing model, as it is done with scalar and tensor perturbations. Under this prescription, one can calculate their evolution during the whole history of the bouncing model, and precisely infer the conditions under which they remain linear before the expanding phase. It is shown that such linearity conditions impose constraints on the free parameters of bouncing models, which are mild, although not trivial, allowing a large class of possibilities. Such conditions impose that vector perturbations are also not observationally relevant in the expanding phase. The conclusion is that bouncing models are generally stable under vector perturbations. As they are also stable under scalar and tensor perturbations, we conclude that bouncing models are generally stable under perturbations originated from quantum vacuum perturbations in the far past of their contracting phase.

Many works have concentrated on the observable signatures of dark matter being an ultralight axionlike particle (ALP). We concentrate on a particularly dramatic signature in the late-time cosmological matter power spectrum that occurs if the symmetry breaking that establishes the ALP happens after inflation—white-noise density fluctuations that dominate at small scales over the adiabatic fluctuations from inflation. These fluctuations alter the early history of nonlinear structure formation. We find that for symmetry-breaking scales of $f_A\sim {10}^{13}-{10}^{15}\mathrm{GeV}$, which require a high effective maximum temperature after inflation, ALP dark matter with a particle mass of $m_A\sim {10}^{-13}-{10}^{-20}\mathrm{eV}$ could significantly change the number of high-redshift dwarf galaxies, the reionization history, and the $\mathrm{Ly}\alpha$ forest. We consider all three observables. We find that the $\mathrm{Ly}\alpha$ forest is the most constraining of current observables, excluding $f_A\gtrsim {10}^{15}\mathrm{GeV}$ ($m_A\lesssim {10}^{-17}\mathrm{eV}$) in the simplest model for the ALP and considerably lower values in models coupled to a hidden asymptotically free strongly interacting sector ($f_A\gtrsim {10}^{13}\mathrm{GeV}$ and $m_A\lesssim {10}^{-13}\mathrm{eV}$). Observations that constrain the extremely high-redshift tail of reionization may disfavor similar levels of isocurvature fluctuations as the forest. Future $z\sim 20–30$ 21 cm observations have the potential to improve these constraints further using that the supersonic motions of the isocurvature-enhanced abundance of $\sim {10}^4{\mathrm{M}}_{\odot }$ halos would shock heat the baryons, sourcing large baryon acoustic oscillation features.

Galactic ultracompact binaries are expected to be the dominant source of gravitational waves in the milli-Hertz frequency band. Of the tens of millions of Galactic binaries with periods shorter than an hour, it is estimated that a few tens of thousand will be resolved by the future Laser Interferometer Space Antenna (LISA). The unresolved remainder will be the main source of “noise” between 1 and 3 mHz. Typical Galactic binaries are millions of years from merger, and consequently their signals will persist for the duration of the LISA mission. Extracting tens of thousands of overlapping Galactic signals and characterizing the unresolved component is a central challenge in LISA data analysis, and a key contribution to arriving at a global solution that simultaneously fits for all signals in the band. Here we present an end-to-end analysis pipeline for Galactic binaries that uses transdimensional Bayesian inference to develop a time-evolving catalog of sources as data arrive from the LISA constellation.

Tidal effects have important imprints on gravitational waves (GWs) emitted during the final stage of the coalescence of binaries that involve neutron stars (NSs). Dynamical tides can be significant when NS oscillations become resonant with orbital motion; understanding this process is important for accurately modeling GW emission from these binaries and for extracting NS information from GW data. In this paper, we use semianalytic methods to carry out a systematic study on the tidal excitation of fundamental modes ($f$-modes) of spinning NSs in coalescencing binaries, focusing on the case when the NS spin is antialigned with the orbital angular momentum—where the tidal resonance is most likely to take place. We first expand NS oscillations into stellar eigenmodes, and then obtain a Hamiltonian that governs the tidally coupled orbit-mode evolution. (Our treatment is at Newtonian order, including a gravitational radiation reaction at quadrupole order.) We then find a new approximation that can lead to analytic expressions of tidal excitations to a high accuracy, and are valid in all regimes of the binary evolution: adiabatic, resonant, and postresonance. Using the method of osculating orbits, we obtain semianalytic approximations to the orbital evolution and GW emission; their agreements with numerical results give us confidence in our understanding of the system’s dynamics. In particular, we recover both the averaged postresonance evolution, which differs from the preresonance point-particle orbit by shifts in orbital energy and angular momentum, as well as instantaneous perturbations driven by the tidal motion. Finally, we use the Fisher matrix technique to study the effect of dynamical tides on parameter estimation. We find that, for a system with component masses of $(1.4,1.4)M_{\odot }$ at 100 Mpc, the constraints on the effective Love number of the (2,2) mode at Newtonian order can be improved by a factor of $3\sim 4$ if spin frequency is as high as 500 Hz. The relative errors are $0.7\sim 0.8$ in the Cosmic Explorer, and they might be further improved by post-Newtonian effects. The constraints on the $f$-mode frequency and the spin frequency are improved by factors of $5\sim 6$ and $19\sim 27$, respectively. In the Cosmic Explorer case, the relative errors are $0.2\sim 0.4$ and $0.7\sim 1.0$, respectively. Hence, the dynamical tides may potentially provide an additional channel to study the physics of NSs. The method presented in this paper is generic and not restricted to $f$-mode; it can also be applied to other types of tides.

We propose a simple model in which the baryon asymmetry and dark matter are created via the decays and inverse decays of QCD-triplet scalars, at least one of which must be in the TeV mass range. Singlet fermions produced in these decays constitute the dark matter. The singlets never reach equilibrium, and their coherent production, propagation, and annihilation generates a baryon asymmetry. We find that the out-of-equilibrium condition and the dark matter density constraint typically require the lightest scalar to be long-lived, giving good prospects for detection or exclusion in current and upcoming colliders. In generalizing the leptogenesis mechanism of Akhmedov, Rubakov and Smirnov, our model expands the phenomenological possibilities for low-scale baryogenesis.

The response of a QCD-like gauge theory, holographically dual to a deformed ${\mathrm{AdS}}_5$ model, to constant electromagnetic fields is thoroughly investigated. The calculations in this paper are performed for three different cases, i.e., with only a quadratic correction, with only a logarithmic correction, and with both quadratic and logarithmic corrections, for which the parameters are chosen as the ones found in [1] by fitting to experimental and lattice results. The critical electric fields of the system are found by analyzing its total potential. Comparing the total potential for the three cases, we observe that the quarks can be liberated easier in quadratic and then logarithmic case, for a given electric field. Then, by calculating the expectation value of a circular Wilson loop, the pair production rate is evaluated while a constant electric field as well as a constant magnetic field are present. The aforementioned result obtained from the potential analysis is also confirmed here when no magnetic fields are present. We moreover find that the presence of a magnetic field perpendicular to the direction of the electric field suppresses the rate of producing the quark pairs and accordingly increases the critical electric field below which the Schwinger effect does not occur. Interestingly, the presence of a parallel magnetic field alone does not change the response of the system to the external electric field, although it enhances the creation rate when a perpendicular magnetic field is also present.

The problem of a scalar particle in a constant crossed electromagnetic field ($\mathbf{E}\perp \mathbf{H}$ and $|\mathbf{E}|=|\mathbf{H}|$) is considered. The high-temperature expansion of the one-loop grand thermodynamic potential and vacuum energy accounting for nonperturbative corrections are derived. The contributions from particles and antiparticles are obtained separately. It is shown that the nonperturbative corrections depend on the boundary conditions but do not depend on the fields.

We study the simplest $SO(2)$ gauged $O(5)$ Skyrme model in $4+1$ (flat) dimensions. In the gauge decoupled limit, the model supports topologically stable solitons (Skyrmions) and after gauging, the static energy of the solutions is bounded from below by a “baryon number.” The studied model features both Maxwell and Maxwell–Chern-Simons dynamics. The considered configurations are subject to biazimuthal symmetry in the ${\mathbb{R}}^4$ subspace resulting in a two dimensional subsystem, as well as subject to an enhanced symmetry relating the two planes in the ${\mathbb{R}}^4$ subspace, which results in a one dimensional subsystem. Numerical solutions are constructed in both cases. In the purely magnetic case, fully biazimuthal solutions were given, while electrically charged and spinning solutions were constructed only in the radial (enhanced symmetric) case, both in the presence of a Chern-Simons term, and in its absence. We find that, in contrast with the analogous models in $2+1$ dimensions, the presence of the Chern-Simons term in the model under study here results only in quantitative effects.

Quantum correlators of pure supersymmetric Yang-Mills theories in $D=3$, 4, 6 and 10 dimensions can be reformulated via the nonlinear and nonlocal transformation (“Nicolai map”) that maps the full functional measure of the interacting theory to that of a free bosonic theory. As a special application we show that for the maximally extended $\mathcal{N}=4$ theory in four dimensions, and up to order $\mathcal{O}(g^2)$, all known results for scalar correlators can be recovered in this way without any use of anticommuting variables, in terms of a purely bosonic and ghost-free functional measure for the gauge fields. This includes in particular the dilatation operator yielding the anomalous dimensions of composite operators. The formalism is thus competitive with more standard perturbative techniques.