We study the plasmon mass scale in classical gluodynamics in a two-dimensional configuration that mimics the boost-invariant initial color fields in a heavy-ion collision. We numerically measure the plasmon mass scale using three different methods: a hard thermal loop (HTL) expression involving the quasiparticle spectrum constructed from Coulomb gauge field correlators, an effective dispersion relation, and the measurement of oscillations between electric and magnetic energies after introducing a spatially uniform perturbation to the electric field. We find that the HTL expression and the uniform electric field measurement are in rough agreement. The effective dispersion relation agrees with other methods within a factor of 2. We also study the dependence on time and occupation number, observing similar trends as in three spatial dimensions, where a power-law dependence sets in after an occupation-number-dependent transient time. We observe a decrease of the plasmon mass squared as $t^{-1/3}$ at late times.

A continuum approach to the three valence-quark bound-state problem in quantum field theory is used to perform a comparative study of the four lightest $(I=1/2,J^P=1/2^{\pm })$ baryon isospin doublets in order to elucidate their structural similarities and differences. Such analyses predict the presence of nonpointlike, electromagnetically active quark-quark (diquark) correlations within all baryons; and in these doublets, isoscalar-scalar, isovector-pseudovector, isoscalar-pseudoscalar, and vector diquarks can all play a role. In the two lightest $(1/2,1/2^{+})$ doublets, however, scalar and pseudovector diquarks are overwhelmingly dominant. The associated rest-frame wave functions are largely $S$-wave in nature; and the first excited state in this $1/2^{+}$ channel has the appearance of a radial excitation of the ground state. The two lightest $(1/2,1/2^{-})$ doublets fit a different picture: accurate estimates of their masses are obtained by retaining only pseudovector diquarks; in their rest frames, the amplitudes describing their dressed-quark cores contain roughly equal fractions of even- and odd-parity diquarks; and the associated wave functions are predominantly $P$-wave in nature, but possess measurable $S$-wave components. Moreover, the first excited state in each negative-parity channel has little of the appearance of a radial excitation. In quantum field theory, all differences between positive- and negative-parity channels must owe to chiral symmetry breaking, which is overwhelmingly dynamical in the light-quark sector. Consequently, experiments that can validate the contrasts drawn herein between the structure of the four lightest $(1/2,1/2^{\pm })$ doublets will prove valuable in testing links between emergent mass generation and observable phenomena and, plausibly, thereby revealing dynamical features of confinement.

The process of neutral-current coherent elastic neutrino-nucleus scattering, consistent with the Standard Model (SM) expectation, has been recently measured by the COHERENT experiment at the Spallation Neutron Source. On the basis of the observed signal and our nuclear calculations for the relevant Cs and I isotopes, the extracted constraints on both conventional and exotic neutrino physics are updated. The present study concentrates on various SM extensions involving vector and tensor nonstandard interactions as well as neutrino electromagnetic properties, with an emphasis on the neutrino magnetic moment and the neutrino charge radius. Furthermore, models addressing a light sterile neutrino state and scenarios with new propagator fields—such as vector $Z^{\prime }$ and scalar bosons—are examined, and the corresponding regions excluded by the COHERENT experiment are presented.

A search for new physics is presented in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from $b$ quarks, and missing transverse momentum ($p_{\mathrm{T}}^{\mathrm{miss}}$). The search uses proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ amounting to $35.9{\mathrm{fb}}^{-1}$ of integrated luminosity collected using the CMS detector in 2016. Hypothetical signal events are efficiently separated from the dominant $t\overline{t}$ background with requirements on $p_{\mathrm{T}}^{\mathrm{miss}}$ and transverse-mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced top squarks. For top squarks, decaying exclusively to a top quark and a neutralino, exclusion limits are placed at 95% confidence level on the mass of the lightest top squark up to 800 GeV and on the lightest neutralino up to 360 GeV. These results, combined with searches in the single-lepton and all-jet final states, raise the exclusion limits up to 1050 GeV for the lightest top squark and up to 500 GeV for the lightest neutralino. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1300 GeV for top squarks and up to 800 GeV for the lightest neutralino. The results are also interpreted in a simplified model with a dark matter (DM) particle coupled to the top quark through a scalar or pseudoscalar mediator. For light DM, mediator masses up to 100 (50) GeV are excluded for scalar (pseudoscalar) mediators. The result for the scalar mediator achieves some of the most stringent limits to date in this model.

A number of long-standing puzzles, such as the origin of extreme-energy cosmic rays, could perhaps be solved if we found a mechanism for effectively transferring energy from black holes to particles and, correspondingly, accelerating the latter to (unboundedly, as long as we neglect the back reaction) large velocities. As of today the only such candidate mechanism in the case of the nonextreme Kerr black hole is colliding a particle that freely falls from infinity with a particle whose trajectory is subject to some special requirements to fulfil which it has to be suitably corrected by auxiliary collisions. In the present paper we prove that—at least when the relevant particles move in the equatorial plane and experience a single correcting collision—this mechanism does not work too. The energy of the final collision becomes unboundedly high only when the energies of the incoming particles do.

A primordial black hole (PBH) is one of the leading nonparticle candidates for dark matter (DM). Although several observations severely constrain the amount of PBHs, it was recently pointed out that there is an uncertainty on the microlensing constraints below $\sim {10}^{-10}{M}_{\odot }$, which was ignored originally but may weaken the constraints significantly. In this paper, facing this uncertainty, we investigate the possibility that PBHs can make up all DM in a broad mass spectrum. Moreover, we propose a concrete inflation model that can simultaneously produce PBHs for all DM in a broad mass spectrum around $\mathcal{O}({10}^{-13})M_{\odot }$ and PBHs for LIGO events in a sharp mass spectrum at $\mathcal{O}(10)M_{\odot }$.

Dissipative dark matter, where dark matter particle properties closely resemble familiar baryonic matter, is considered. Mirror dark matter, which arises from an isomorphic hidden sector, is a specific and theoretically constrained scenario. Other possibilities include models with more generic hidden sectors that contain massless dark photons [unbroken $U(1)$ gauge interactions]. Such dark matter not only features dissipative cooling processes but also is assumed to have nontrivial heating sourced by ordinary supernovae (facilitated by the kinetic mixing interaction). The dynamics of dissipative dark matter halos around rotationally supported galaxies, influenced by heating as well as cooling processes, can be modeled by fluid equations. For a sufficiently isolated galaxy with a stable star formation rate, the dissipative dark matter halos are expected to evolve to a steady state configuration which is in hydrostatic equilibrium and where heating and cooling rates locally balance. Here, we take into account the major cooling and heating processes, and numerically solve for the steady state solution under the assumptions of spherical symmetry, negligible dark magnetic fields, and that supernova sourced energy is transported to the halo via dark radiation. For the parameters considered, and assumptions made, we were unable to find a physically realistic solution for the constrained case of mirror dark matter halos. Halo cooling generally exceeds heating at realistic halo mass densities. This problem can be rectified in more generic dissipative dark matter models, and we discuss a specific example in some detail.

We present a description of electrons propagating in an elliptically polarized, plane wave background which includes circular and linear polarizations as special cases. We calculate, to all orders in the background field, the two point function and relate it to various expressions found in the literature. The background field induced mass shift of the electron is shown to be polarization independent in the full elliptic class. The matrix nature of this mass shift in the fermionic theory is discussed. The extent to which a momentum space description is possible for this system is clarified.

The truncation formulas of $D=11$ supergravity on $S^7$ to $D=4$ $\mathcal{N}=8$ SO(8)-gauged supergravity are completed to include the full nonlinear dependence of the $D=11$ three-form potential ${\widehat{A}}_{(3)}$ on the $D=4$ fields, and their consistency is shown. The full embedding into ${\widehat{A}}_{(3)}$ is naturally expressed in terms of a restricted version, still $\mathcal{N}=8$ but only SL(8)–covariant, of the $D=4$ tensor hierarchy. The redundancies introduced by this approach are removed at the level of the field strength ${\widehat{F}}_{(4)}$ by exploiting $D=4$ duality relations. Finally, new expressions for the full consistent truncation formulas are given that are explicit in all $D=11$ and $D=4$ fields.

Einstein originally proposed a nonsymmetric tensor field, with its symmetric part associated with the spacetime metric and its antisymmetric part associated with the electromagnetic field, as an approach to a unified field theory. Here we interpret it more modestly as an alternative to Einstein-Maxwell theory, approximating the coupling between the electromagnetic field and spacetime curvature in the macroscopic classical regime. Previously it was shown that the Lorentz force can be derived from this theory, albeit with deviation on the scale of a universal length constant $\ell$. Here we assume that $\ell$ is of galactic scale and show that the modified coupling of the electromagnetic field with charged particles allows a non-Maxwellian equilibrium of non-neutral plasma. The resulting electromagnetic field is “dark” in the sense that its modified Lorentz force on the plasma vanishes, yet through its modified coupling to the gravitational field it engenders a nonvanishing, effective mass density. We obtain a solution for which this mass density asymptotes approximately to that of the pseudoisothermal model of dark matter. The resulting gravitational field produces radial acceleration, in the context of a post-Minkowskian approximation, which is negligible at small radius but yields a flat rotation curve at large radius. We further exhibit a family of such solutions which, like the pseudoisothermal model, has a free parameter to set the mass scale (in this case related to the charge density) and a free parameter to set the length scale (in this case an integer multiple of $\ell$). Moreover, these solutions are members of a larger family with more general angular and radial dependence. They thus show promise as approximations of generalized pseudoisothermal models, which in turn are known to fit a wide range of mass density profiles for galaxies and clusters.

The introduction of dark matter-neutrino interactions modifies the cosmic microwave background (CMB) angular power spectrum at all scales, thus affecting the reconstruction of the cosmological parameters. Such interactions can lead to a slight increase of the value of $H_0$ and a slight decrease of $S_8\equiv {\sigma }_8\sqrt{{\mathrm{\Omega }}_m/0.3}$, which can help reduce somewhat the tension between the CMB and weak lensing or Cepheids data sets. Here we show that it is impossible to solve both tensions simultaneously. While the 2015 Planck temperature and low multipole polarization data combined with the Cepheids data sets prefer large values of the Hubble rate (up to $H_0={72.1}_{-1.7}^{+1.5}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, when $N_{\mathrm{eff}}$ is free to vary), the ${\sigma }_8$ parameter remains too large to reduce the ${\sigma }_8$ tension. Adding high multipole Planck polarization data does not help since this data shows a strong preference for low values of $H_0$, thus worsening current tensions, even though they also prefer smaller value of ${\sigma }_8$.

Cosmological measurements of structure are placing increasingly strong constraints on the sum of the neutrino masses, $\mathrm{\Sigma }{m}_{\nu }$, through Bayesian inference. Because these constraints depend on the choice for the prior probability $\pi (\mathrm{\Sigma }{m}_{\nu })$, we argue that this prior should be motivated by fundamental physical principles rather than the ad hoc choices that are common in the literature. The first step in this direction is to specify the prior directly at the level of the neutrino mass matrix $M_{\nu }$, since this is the parameter appearing in the Lagrangian of the particle physics theory. Thus by specifying a probability distribution over $M_{\nu }$, and by including the known squared mass splittings, we predict a theoretical probability distribution over $\mathrm{\Sigma }{m}_{\nu }$ that we interpret as a Bayesian prior probability $\pi (\mathrm{\Sigma }{m}_{\nu })$. Assuming a basis-invariant probability distribution on $M_{\nu }$, also known as the anarchy hypothesis, we find that $\pi (\mathrm{\Sigma }{m}_{\nu })$ peaks close to the smallest $\mathrm{\Sigma }{m}_{\nu }$ allowed by the measured mass splittings, roughly 0.06 eV (0.1 eV) for normal (inverted) ordering, due to the phenomenon of eigenvalue repulsion in random matrices. We consider three models for neutrino mass generation: Dirac, Majorana, and Majorana via the seesaw mechanism; differences in the predicted priors $\pi (\mathrm{\Sigma }{m}_{\nu })$ allow for the possibility of having indications about the physical origin of neutrino masses once sufficient experimental sensitivity is achieved. We present fitting functions for $\pi (\mathrm{\Sigma }{m}_{\nu })$, which provide a simple means for applying these priors to cosmological constraints on the neutrino masses or marginalizing over their impact on other cosmological parameters.

In the standard approach to studying cosmological structure formation, the overall expansion of the Universe is assumed to be homogeneous, with the gravitational effect of inhomogeneities encoded entirely in a Newtonian potential. A topic of ongoing debate is to what degree this fully captures the dynamics dictated by general relativity, especially in the era of precision cosmology. To quantitatively assess this, we directly compare standard N-body Newtonian calculations to full numerical solutions of the Einstein equations, for cold matter with various magnitude initial inhomogeneities on scales comparable to the Hubble horizon. We analyze the differences in the evolution of density, luminosity distance, and other quantities defined with respect to fiducial observers. This is carried out by reconstructing the effective spacetime and matter fields dictated by the Newtonian quantities, and by taking care to distinguish effects of numerical resolution. We find that the fully general relativistic and Newtonian calculations show excellent agreement, even well into the nonlinear regime. They only notably differ in regions where the weak gravity assumption breaks down, which arise when considering extreme cases with perturbations exceeding standard values.

We consider the relationship between fluid models of an interacting dark sector and the field theoretical models that underlie such descriptions. This question is particularly important in light of suggestions that such interactions may help alleviate a number of current tensions between different cosmological datasets. We construct consistent field theory models for an interacting dark sector that behave exactly like the coupled fluid ones, even at the level of linear perturbations, and can be trusted deep in the nonlinear regime. As a specific example, we focus on the case of a Dirac, Born-Infeld (DBI) field conformally coupled to a quintessence field. We show that the fluid linear regime breaks before the field gradients become large; this means that the field theory is valid inside a large region of the fluid nonlinear regime.

We study the effects of nonstandard self-interactions (NSSI) of neutrinos streaming out of a core-collapse supernova. We show that with NSSI, the standard linear stability analysis gives rise to linearly as well as exponentially growing solutions. For a two-box spectrum, we demonstrate analytically that flavor-preserving NSSI lead to a suppression of bipolar collective oscillations. In the intersecting four-beam model, we show that flavor-violating NSSI can lead to fast oscillations even when the angle between the neutrino and antineutrino beams is obtuse, which is forbidden in the standard model. This leads to the new possibility of fast oscillations in a two-beam system with opposing neutrino-antineutrino fluxes, even in the absence of any spatial inhomogeneities. Finally, we solve the full nonlinear equations of motion in the four-beam model numerically, and explore the interplay of fast and slow flavor conversions in the long-time behavior, in the presence of NSSI.

We revisit the status of a Majorana fermion as a dark matter candidate when a sequential $Z^{\prime }$ gauge boson dictates the dark matter phenomenology. Direct dark matter detection signatures rise from dark matter-nucleus scatterings at bubble chamber and liquid xenon detectors, and from the flux of neutrinos from the Sun measured by the IceCube experiment, which is governed by the spin-dependent dark matter-nucleus scattering. On the collider side, LHC searches for dilepton and monojet + missing energy signals play an important role. The relic density and perturbativity requirements are also addressed. By exploiting the dark matter complementarity we outline the region of parameter space where one can successfully have a Majorana dark matter particle in light of current and planned experimental sensitivities.

We study a dark matter (DM) model offering a very natural explanation of two (naively unrelated) problems in cosmology: the observed relation ${\mathrm{\Omega }}_{\mathrm{DM}}\sim {\mathrm{\Omega }}_{\text{visible}}$ and the observed asymmetry between matter and antimatter in the Universe, known as the “baryogenesis” problem. In this framework, both types of matter (dark and visible) have the same QCD origin, form at the same QCD epoch, and are proportional to one and the same dimensional parameter of the system, ${\mathrm{\Lambda }}_{\mathrm{QCD}}$, which explains how these two naively distinct problems could be intimately related, and could be solved simultaneously within the same framework. More specifically, the DM in this model is composed by two different ingredients: the (well-studied) DM axions and the (less-studied) quark nuggets made of matter or antimatter. We focus on the quantitative analysis of the relation between these two distinct components contributing to the dark sector of the theory determined by ${\mathrm{\Omega }}_{\mathrm{DM}}\equiv [{\mathrm{\Omega }}_{\mathrm{DM}}(\text{nuggets})+{\mathrm{\Omega }}_{\mathrm{DM}}(\text{axion})]$. We argue that the nuggets’ DM component always traces the visible matter density, i.e., ${\mathrm{\Omega }}_{\mathrm{DM}}(\text{nuggets})\sim {\mathrm{\Omega }}_{\text{visible}}$, and this feature is not sensitive to the parameters of the system such as the axion mass $m_a$ or the misalignment angle ${\theta }_0$. It should be contrasted with conventional axion production mechanisms due to the misalignment when ${\mathrm{\Omega }}_{\mathrm{DM}}(\text{axion})$ is highly sensitive to the axion mass $m_a$ and the initial misalignment angle ${\theta }_0$. We also discuss the constraints on this model related to the inflationary scale $H_I$, nonobservation of the isocurvature perturbations and the tensor modes. We also comment on some constraints related to various axion search experiments.

On August 17, 2017 the LIGO interferometers detected the gravitational wave (GW) signal (GW170817) from the coalescence of binary neutron stars. This signal was also simultaneously seen throughout the electromagnetic (EM) spectrum from radio waves to gamma rays. We point out that this simultaneous detection of GW and EM signals rules out a class of modified gravity theories, termed “dark matter emulators,” which dispense with the need for dark matter by making ordinary matter couple to a different metric from that of GW. We discuss other kinds of modified gravity theories which dispense with the need for dark matter and are still viable. This simultaneous observation also provides the first observational test of Einstein’s weak equivalence principle (WEP) between gravitons and photons. We estimate the Shapiro time delay due to the gravitational potential of the total dark matter distribution along the line of sight (complementary to the calculation by Abbott et al. [Astrophys. J. Lett. 848, L13 (2017)]) to be about 400 days. Using this estimate for the Shapiro delay and from the time difference of 1.7 seconds between the GW signal and gamma rays, we can constrain violations of the WEP using the parametrized post-Newtonian parameter $\gamma$, and it is given by $|{\gamma }_{\mathrm{GW}}-{\gamma }_{\mathrm{EM}}|<9.8\times {10}^{-8}$.

In this paper we perform an amplitude analysis of ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}\gamma$ and confront it with the latest BESIII data. Based on the final-state interaction theorem, we represent the amplitude in terms of an Omnés function multiplied by a form factor that corresponds to the contributions from left-hand cuts and right-hand cuts in the inelastic channels. We also take into account the isospin violation effect induced by $\rho -\omega$ mixing. Our results show that the anomaly contribution is mandatory in order to explain the data. Its contribution to the decay width of $\mathrm{\Gamma }({\eta }^{\prime }\to \pi \pi \gamma )$ is larger than that induced by isospin violation. Finally we extract the pole positions of the $\rho$ and $\omega$ as well as their corresponding residues.

We consider the production of two Higgs bosons in association with a gauge boson or another Higgs boson at the hadron colliders. We compute the cross sections and distributions for the processes $pp\to HHH$ and $HHZ$ within the standard model. In particular, we compute the gluon-gluon fusion one-loop contributions mediated via heavy quarks in the loop. It is the leading order contribution to $pp\to HHH$ process. To the process $pp\to HHZ$, it is next-to-next-to-leading-order (NNLO) contribution in QCD coupling. We also compare this contribution to the next-to-leading-order (NLO) QCD contribution to this process. The NNLO contribution can be similar to NLO contribution at the Large Hadron Collider (LHC), and significantly more at higher center-of-mass energy machines. We also study new physics effects in these processes by considering $ttH$, $HHH$, $HHHH$, $HZZ$, and $HHZZ$ interactions as anomalous. The anomalous couplings can enhance the cross sections significantly. The $gg\to HHH$ process is specially sensitive to anomalous trilinear Higgs boson self-coupling. For the $gg\to HHZ$ process, there is some modest dependence on anomalous $HZZ$ couplings.