The hot big bang is often considered as the origin of all matter and radiation in the Universe. Primordial nucleosynthesis provides strong evidence that the early Universe contained a hot plasma of photons and baryons with a temperature $T>\mathrm{MeV}$. However, the earliest probes of dark matter originate from much later times around the epoch of structure formation. In this work we describe a scenario in which dark matter (and possibly dark radiation) can be formed around or even after primordial nucleosynthesis in a second big bang, which we dub the “dark big bang.” The latter occurs through a phase transition in the dark sector that transforms dark vacuum energy into a hot dark plasma of particles; in this paper we focus on a first-order phase transition for the dark big bang. The correct dark matter abundance can be set by dark matter cannibalism or by pair annihilation within the dark sector followed by a thermal freeze-out. Alternatively ultraheavy “dark-zilla” dark matter can originate directly from bubble collisions during the dark big bang. We will show that the dark big bang is consistent with constraints from structure formation and the cosmic microwave background if it occurred when the Universe was less than one month old, corresponding to a temperature in the visible sector above $\mathcal{O}(\mathrm{keV})$. While the dark matter evades direct and indirect detection, the dark big bang gives rise to striking gravity wave signatures to be tested at pulsar timing array experiments. Furthermore, the dark big bang allows for realizations of self-interacting and/or warm dark matter, which suggest exciting discovery potential in future small-scale structure observations.

The widely used MASTER approach for angular power spectrum estimation was developed as a fast $C_{\ell }$ estimator on limited regions of the sky. This method expresses the power spectrum of a masked map (“pseudo-$C_{\ell }$”) in terms of the power spectrum of the unmasked map (the true $C_{\ell }$) and that of the mask or weight map. However, it is often the case that the map and mask are correlated in some way, such as point source masks used in cosmic microwave background (CMB) analyses, which have nonzero correlation with CMB secondary anisotropy fields and other mm-wave sky signals. In such situations, the MASTER approach gives biased results, as it assumes that the unmasked map and mask have zero correlation. While such effects have been discussed before with regard to specific physical models, here we derive a completely general formalism for any case where the map and mask are correlated. We show that our result (“reMASTERed”) reconstructs ensemble-averaged pseudo-$C_{\ell }$ to effectively exact precision, with significant improvements over traditional estimators for cases where the map and mask are correlated. In particular, we obtain an improvement in the mean absolute percent error from 30% with the MASTER result to essentially no error with the reMASTERed result for an integrated Sachs-Wolfe (ISW) field map with a mask built from the thresholded ISW field, and 10% to effectively zero for a Compton-$y$ map combined with an infrared source mask (the latter being directly relevant to actual data analysis). An important consequence of our result is that for maps with correlated masks, it is no longer possible to invert a simple equation to obtain the true $C_{\ell }$ from the pseudo-$C_{\ell }$. Instead, our result necessitates the use of forward modeling from theory space into the observable domain of the pseudo-$C_{\ell }$. Our code is publicly available in reMASTERed.

https://github.com/kmsurrao/reMASTERed.

The linear matter power spectrum $P(k,z)$ connects theory with large scale structure observations in cosmology. Its scale dependence is entirely encoded in the matter transfer function $T(k)$, which can be computed numerically by Boltzmann solvers, and can also be computed semianalytically by using fitting functions such as the well-known Bardeen-Bond-Kaiser-Szalay (BBKS) and Eisenstein-Hu (EH) formulas. However, both the BBKS and EH formulas have some significant drawbacks. On the one hand, although BBKS is a simple expression, it is only accurate up to 10%, which is well above the 1% precision goal of forthcoming surveys. On the other hand, while EH is as accurate as required by upcoming experiments, it is a rather long and complicated expression. Here, we use the genetic algorithms (GAs), a particular machine learning technique, to derive simple and accurate fitting formulas for the transfer function $T(k)$. When the effects of massive neutrinos are also considered, our expression slightly improves over the EH formula, while being notably shorter in comparison.

Quantum entanglement between the two $W$ bosons resulting from the decay of a Higgs boson may be investigated in the dilepton channel $H\to WW\to \ell \nu \ell \nu$ using laboratory-frame observables that only involve the charged leptons $\ell =e$, $\mu$. The dilepton invariant mass distribution, already measured by the ATLAS and CMS Collaborations at the LHC, can be used to observe the quantum entanglement of the $WW$ pair with a statistical sensitivity of $7\sigma$ with run 2 data, and of $6\sigma$ when including theoretical systematics. As a by-product, the relation between $W$ rest frame (four-dimensional) angular distributions, $H\to WW$ decay amplitudes, and spin correlation coefficients, is written down.

We study the electrodynamics of a kinetically mixed dark photon cloud that forms through superradiance around a spinning black hole, and design strategies to search for the resulting multimessenger signals. A dark photon superradiance cloud sources a rotating dark electromagnetic field which, through kinetic mixing, induces a rotating visible electromagnetic field. Standard model charged particles entering this field initiate a transient phase of particle production that populates a plasma inside the cloud and leads to a system which shares qualitative features with a pulsar magnetosphere. We study the electrodynamics of the dark photon cloud with resistive magnetohydrodynamics methods applicable to highly magnetized plasma, adapting techniques from simulations of pulsar magnetospheres. We identify turbulent magnetic field reconnection as the main source of dissipation and electromagnetic emission, and compute the peak luminosity from clouds around solar-mass black holes to be as large as ${10}^{43}\mathrm{erg}/\mathrm{s}$ for observationally allowed dark photon parameter space. The emission is expected to have a significant x-ray component and to potentially be periodic, with period set by the dark photon mass. The luminosity is comparable to the brightest x-ray sources in the Universe, allowing for searches at distances of up to hundreds of Mpc with existing telescopes. We discuss observational strategies, including targeted electromagnetic follow-ups of solar-mass black hole mergers and targeted continuous gravitational wave searches of anomalous pulsars.

We use the two-flavor Linear Sigma Model with quarks to study the phase structure of isospin asymmetric matter at zero temperature. The meson degrees of freedom provide the mean field chiral and isospin condensates on top of which we compute the effective potential accounting for constituent quark fluctuations at one-loop order. Using the renormalizability of the model, we absorb the ultraviolet divergences into suitable counterterms that are added respecting the original structure of the theory. These counterterms are determined from the stability conditions which require the effective potential to have minima in the condensates directions at the classical values, as well as the transition from the noncondensed to the condensed phase to be smooth as a function of the isospin chemical potential. We use the model to study the evolution of the condensates as well as the pressure, energy and isospin densities and the sound velocity as functions of the isospin chemical potential. The approach does a good average description up to isospin chemical potentials values not too large as compared to the vacuum pion mass.

We explore the analytic structure of three-point functions using contour deformations. This method allows continuing calculations analytically from the spacelike to the timelike regime. We first elucidate the case of two-point functions with explicit explanations how to deform the integration contour and the cuts in the integrand to obtain the known cut structure of the integral. This is then applied to one-loop three-point integrals. We explicate individual conditions of the corresponding Landau analysis in terms of contour deformations. In particular, the emergence and position of singular points in the complex integration plane are relevant to determine the physical thresholds. As an exploratory demonstration of this method’s numerical implementation we apply it to a coupled system of functional equations for the propagator and the three-point vertex of ${\varphi }^3$ theory. We demonstrate that under generic circumstances the three-point vertex function displays cuts which can be determined from modified Landau conditions.

We examine the endpoint region of inclusive deep inelastic scattering at next-to-leading power (NLP). Using a soft-collinear effective theory approach with no explicit soft or collinear modes, we discuss the factorization of the cross section at NLP and show that the overlap subtraction procedure introduced to eliminate double counting of degrees of freedom at leading power ensures that spurious endpoint divergences in the rate cancel at NLP at one loop. For this cancellation to occur at all renormalization scales a nontrivial relation between the anomalous dimensions of the leading and subleading operators is required, which is demonstrated to hold at one loop.

We propose a kinematic algebra for the Bern-Carrasco-Johansson (BCJ) numerators of tree-level amplitudes and form factors in Yang-Mills theory coupled with biadjoint scalars. The algebraic generators of the algebra contain two parts: the first part is simply the flavor factor of the biadjoint scalars, and the second part that maps to nontrivial kinematic structures of the BCJ numerators obeys extended quasishuffle fusion products. The underlying kinematic algebra allows us to present closed forms for the BCJ numerators with any number of gluons and two or more scalars for both on-shell amplitudes and form factors that involve an off-shell operator. The BCJ numerators constructed in this way are manifestly gauge invariant and obey many novel relations that are inherited from the kinematic algebra.

We propose a new mechanism to dynamically select the electroweak scale during inflation. An axionlike field $\varphi$ that couples quadratically to the Higgs moves with a large initial velocity towards a critical point ${\varphi }_c$ where the Higgs becomes massless. When $\varphi$ crosses this point, it enters a region where the Higgs mass is tachyonic and this results into an explosive production of Higgs particles. Consequently, a backreaction potential is generated and the field $\varphi$ is attracted back to ${\varphi }_c$. After a series of oscillations around this point it is eventually trapped in its vicinity due to the periodic term of the potential. The model avoids trans-Planckian field excursions, requires very few $e$-folds of inflation and it is compatible with inflation scales up to ${10}^5\mathrm{GeV}$. The mass of $\varphi$ lies in the range of hundreds of GeV to a few TeV and it can be potentially probed in future colliders.

We discuss self-gravitating global O(3) monopole solutions associated with the spontaneous breaking of O(3) down to a global O(2) in an extended Gauss-Bonnet theory of gravity in ($3+1$) dimensions, in the presence of a nontrivial scalar field $\mathrm{\Phi }$ that couples to the Gauss-Bonnet higher curvature combination with a coupling parameter $\alpha$. We obtain a range of values for $\alpha <0$ (in our notation and conventions), which are such that a global (Israel type) matching is possible of the space-time exterior to the monopole core $\delta$ with a de Sitter interior, guaranteeing the positivity of the Arnowitt-Deser-Misner (ADM) mass of the monopole, which, together with a positive core radius $\delta >0$, are both dynamically determined as a result of this matching. It should be stressed that in the general relativity (GR) limit, where $\alpha \to 0$, and $\mathrm{\Phi }\to \text{constant}$, such a matching yields a negative ADM monopole mass, which might be related to the stability issues the [Barriola-Vilenkin (BV)] global monopole of GR faces. Thus, our global monopole solution, which shares many features with the BV monopole, such as an asymptotic-space-time deficit angle, of potential phenomenological/cosmological interest, but has, par contrast, a positive ADM mass, has a chance of being a stable configuration, although a detailed stability analysis is pending.

Theories of scalars and gravity, with an Einstein-Hilbert term and nonminimal interactions, $M^{2}R/2-\alpha {\varphi }^{2}R/12$, have graviton exchange-induced contact interactions. These modify the renormalization group, leading to a discrepancy between the conventional calculations in the Jordan frame that ignore this effect (and are found to be incorrect), and the Einstein frame in which $\alpha$ does not exist. Thus, the calculation of quantum effects in the Jordan and Einstein frames does not generally commute with the transition from the Jordan to the Einstein frame. In the Einstein frame, though $\alpha$ is absent, for small steps in scale $\delta \mu /\mu$ infinitesimal contact terms $\sim \delta \alpha$ are induced, that are then absorbed back into other couplings by the contact terms. This modifies the $\beta$-functions in the Einstein frame. We show how correct results can be obtained in a simple model by including this effect.

In modified gravity models that allow for additional noncompact spacetime dimensions, energy from gravitational waves can leak into these extra spacetime dimensions, leading to a reduction in the amplitude of the observed gravitational waves, and thus are a source of potential systematics in the inferred luminosity distances to gravitational wave sources. Since binary black hole (BBH) mergers are standard sirens, we use the pair-instability supernova mass gap and its predicted features to determine a mass scale in order to break the mass-redshift degeneracy and thus infer the redshift of the source. We simultaneously fit the BBH population and the extra spacetime dimensions parameters from gravitational leakage models using BBH observations from the recently released GWTC-3 catalog. We set constraints on the number of spacetime dimensions and find that $D=3.93_{-0.05}^{+0.08}$ at 68% C.L. for models that are independent of a screening scale, finding that the GWTC-3 constraint is as competitive as that set from GW170817 and its electromagnetic counterpart. For models where gravity leaks below a certain screening scale $R_c$, we find $D=4.49_{-0.87}^{+1.63}$ and ${\log }_{10}{R}_c/\mathrm{Mpc}=4.75_{-0.99}^{+0.86}$ with a transition steepness ${\log }_{10}n=0.85_{-0.86}^{+0.76}$ for the leakage, which for the first time are constrained jointly with the BBH population at cosmological distances. These constraints are consistent with General Relativity (GR), where gravitational waves propagate in $D=3+1$ spacetime dimensions. Using the BBH population to probe modifications to standard cosmological models provides an independent test of GR that does not rely on any electromagnetic information but purely on gravitational wave observations.

We present a mechanism for generating ultralight dark photon dark matter in the early Universe via a dilatonlike scalar field coupled to the dark photon’s kinetic term. Energy is initially stored in the condensate of the dilaton, which resonantly produces dark photons when it begins oscillating in the early Universe. While similar scenarios with axion–dark-photon couplings require large coupling coefficients to fully populate the dark photon, the dilatonic coupling features a unique regime: When the dark photon’s mass is half that of the dilaton, dark photons are copiously produced even when the dilaton undergoes small-amplitude oscillations. Scenarios consistent with the cosmic microwave background allow for ultralight vector dark matter with mass as light as ${10}^{-20}\mathrm{eV}$.

We find several missing one-loop-order contributions in previous considerations about secondary gravitational waves induced at nonlinear order in cosmological perturbations. We consider a consistent perturbative expansion to third order in cosmological perturbations, including higher-order interactions and iterative solutions ignored in the previous literature. Tensor fluctuations induced by the source with two scalar and one tensor perturbations are correlated with the first-order tensor fluctuation and thus give a one-loop order correction to the tensor-power spectrum. The missing loop correction is scale invariant and negative in the superhorizon region, which secondarily reduces the initial primordial tensor-power spectrum prior to the horizon reentry. Such an IR behavior is very different from the autospectrum of second-order induced tensor modes discussed in the previous literature and can be important for the actual gravitational wave measurements. For a sharp peak of scalar fluctuations with $A_{\zeta }={10}^{-2}$ at $k_{*}={10}^{5}h/\mathrm{Mpc}$ motivated by the LIGO/Virgo events, we show that the tensor-power spectrum at the cosmic microwave background scale reduces by at most 35%. Hence, the polarization B mode might not be seen because of the reduction of the original tensor spectrum due to the secondary effect of primordial black hole formation.

Many theories beyond the Standard Model of particle physics predict the existence of axionlike particles (ALPs) that mix with photons in the presence of a magnetic field. Searching for the effects of ALP-photon mixing in gamma-ray observations of blazars has provided some of the strongest constraints on ALP parameter space so far. Previously, only individual sources have been analyzed. We perform a combined analysis on Fermi Large Area Telescope data of three bright flaring flat-spectrum radio quasars, with the blazar jets themselves as the dominant mixing region. For the first time, we include a full treatment of photon-photon dispersion within the jet and account for the uncertainty in our $B$-field model by leaving the field strength free in the fitting. Overall, we find no evidence for ALPs but are able to exclude the ALP parameters $5\mathrm{neV}\lesssim m_a\lesssim 200\mathrm{neV}$ and $g_{a\gamma }\gtrsim 5\times {10}^{-12}{\mathrm{GeV}}^{-1}$ with 95% confidence.

Very-high-energy (VHE) gamma rays and charged cosmic rays (CCRs) provide an observational window into the acceleration mechanisms of extreme astrophysical environments. One of the major challenges at imaging air Cherenkov telescopes (IACTs) designed to look for VHE gamma rays, is the separation of air showers initiated by CCRs which form a background to gamma-ray searches. Two other less well-studied problems at IACTs are (a) the classification of different primary nuclei among the CCR events, and (b) identification of anomalous events initiated by beyond-the-Standard-Model (BSM) particles that could give rise to shower signatures which differ from the standard images of either gamma rays or CCR showers. The problems of categorizing the primary particle that initiates a shower image, or the problem of tagging anomalous shower events in a model-independent way, are problems that are well suited to a machine learning approach. Traditional studies that have explored gamma-ray/CCR separation have used a multivariate analysis based on derived shower properties, which contains significantly reduced information about the shower. In our work, we address the problems outlined above by using machine learning architectures trained on full simulated shower images, as opposed to training on just a few derived shower properties. We illustrate the techniques of binary and multicategory classification using convolutional neural networks, and we also pioneer the use of autoencoders for anomaly detection at VHE gamma-ray experiments. The latter technique has been studied previously in the context of collider physics, to tag anomalous BSM candidates in a model-independent way. In this study, for the first time, we demonstrate the efficacy of these techniques in the domain of VHE gamma-ray experiments. As a case study, we apply our techniques to the High Energy Stereoscopic System experiment. However, the real strength of the techniques that we broach here in the context of VHE gamma-ray observatories, is that these methods can be applied broadly to any other IACT—such as the upcoming Cherenkov Telescope Array—or can even be suitably adapted to CCR experiments.

It has been shown recently that quark-hadron conversions at the interface of a hybrid star may have a key role on the dynamic stability of the compact object. In this work we perform a systematic study of hybrid stars with reactive interfaces using a model-agnostic piecewise-polytropic hadronic equation of state and the Nambu–Jona-Lasinio (NJL) model for three-flavor quark matter. For the hadronic phase we use a soft, an intermediate and a stiff parametrization that match at $1.1n_0$ with predictions based on chiral effective field theory (cEFT) interactions. In the NJL Lagrangian we include scalar, vector and ’t Hooft interactions. The vector coupling constant $g_v$ is treated as a free parameter. We also consider that there is a split between the deconfinement and the chiral phase transitions which is controlled by changing the conventional value of the vacuum pressure $-{\mathrm{\Omega }}_0$ in the NJL thermodynamic potential by $-({\mathrm{\Omega }}_0+\delta {\mathrm{\Omega }}_0)$, being $\delta {\mathrm{\Omega }}_0$ a free parameter. We analyze the mass-radius ($M\text{−}R$) relation in the case of rapid ($\tau \ll 1\mathrm{ms}$) and slow ($\tau \gg 1\mathrm{ms}$) conversions, being $\tau$ the reaction timescale. In the case of slow interface reactions we find $M\text{−}R$ curves with a cusp at the maximum mass point where a pure hadronic branch and a slow-stable hybrid star (SSHS) branch coincide. We find that the length of the slow-stable branch grows with the increase of the transition density and the energy density jump at the hadron-quark interface. We calculate the tidal deformabilities of SSHSs and analyze them in the light of the GW170817 event.

Very recently, the Pierre Auger and Telescope Array collaborations reported strong evidence for a correlation between the highest energy cosmic rays and nearby starburst galaxies, with a global significance post-trial of $4.7\sigma$. It is well-known that the collective effect of supernovae and winds from massive stars in the central region of these galaxies drives a galactic-scale superwind that can shock heat and accelerate ambient interstellar or circumgalactic gas. In previous work we showed that, for reasonable source parameters, starburst-driven superwinds can be the carriers of ultrahigh-energy cosmic ray acceleration. In this paper we assess the extent to which one can approach the archaeological “inverse” problem of deciphering properties of superwind evolution from present-day IR emission of their host galaxies. We show that the Outer Limits galaxy NGC 891 could provide “smoking-gun evidence” for the starburst-driven superwind model of ultrahigh-energy cosmic rays.

Superconducting detectors have been proposed as outstanding targets for the direct detection of light dark matter scattering at masses as low as a keV. We study the prospects for directional detection of dark matter in isotropic superconducting targets from the angular distribution of excitations produced in the material. We find that dark matter scattering produces initial excitations with an anisotropic distribution, and further show that this directional information can be preserved as the initial excitations relax. Our results demonstrate that directional detection is possible for a wide range of dark matter masses, and they pave the way for light dark matter discovery with bulk superconducting targets.