Despite all fundamental objections against Newtonian concepts in cosmology, the Friedmann equation derives from these in an astoundingly simple way through application of the shell theorem and conservation of Newtonian energy in an infinite universe. However, Friedmann universes in general possess a finite gravitational horizon, as a result of which the application of the shell theorem fails and the Newtonian derivation collapses. Hence, unlike the general relativistic derivation, the Newtonian derivation does not prove the Friedmann equation in general, but exclusively in the Newtonian case of an infinite horizon. We show that in the presence of a gravitational horizon the Friedmann equation can be derived from conservation of Machian energy, without invoking the shell theorem. Whereas in the Newtonian case total energy translates to curvature energy density, in the Machian case total energy takes on different identities, depending on the evolution of the horizon; we show that in the de Sitter universe Machian total energy density is constant, i.e. appears as cosmological constant.

The equivalence of the noncommutative U(N) quantum field theories related by the $\theta$-exact Seiberg-Witten maps is, in this paper, proven to all orders in the perturbation theory with respect to the coupling constant. We show that this holds for super Yang-Mills theories with $\mathcal{N}=0$, 1, 2, 4 supersymmetry. A direct check of this equivalence relation is performed by computing the one-loop quantum corrections to the quadratic part of the effective action in the noncommutative U(1) gauge theory with $\mathcal{N}=0$, 1, 2, 4 supersymmetry.

In supersymmetric models with radiatively driven naturalness, Higgsino-like electroweak-inos are expected to lie in a mass range 100–300 GeV, the lighter the more natural. Such states can be pair produced at high rates at the International Linear $e^{+}{e}^{-}$ Collider where their masses are nearly equal to the value of the superpotential $\mu$ parameter while their mass splittings depend on the gaugino masses $M_1$ and $M_2$. The gaugino masses in turn depend on trilinear soft terms—the $A$ parameters, which are expected to lie in the multi-TeV range owing to the 125 GeV Higgs mass—via two-loop contributions to renormalization group running. We examine the extent to which the International Linear $e^{+}{e}^{-}$ Collider is sensitive to large $A$ terms via precision electroweak-ino mass measurement. Extraction of gaugino masses at the percent level or below should allow for interesting probes of large trilinear soft supersymmetry breaking terms under the assumption of unified gaugino masses.

We analyze the present bounds of a scotogenic model, the radiative type III seesaw, in which an additional scalar doublet and at least two fermion triplets of $SU(2{)}_L$ are added to the Standard Model. In the radiative type III seesaw, the new physics (NP) sector is odd under an exact global ${\mathbf{Z}}_2$ symmetry. This symmetry guaranties that the lightest NP neutral particle is stable, providing a natural dark matter candidate, and leads to naturally suppressed neutrino masses generated by a one-loop realization of an effective Weinberg operator. We focus on the region with the highest sensitivity in present and future LHC searches, with light scalar dark matter and at least one NP fermion triplet at the sub-TeV scale. This region allows for significant production cross sections of NP fermion pairs at the LHC. We reinterpret a set of searches for supersymmetric particles at the LHC obtained using the package CheckMATE, to set limits on our model as a function of the masses of the NP particles and their Yukawa interactions. The most sensitive search channel is found to be dileptons plus missing transverse energy. In order to target the case of tau enhanced decays and the case of compressed spectra, we reinterpret the recent slepton and chargino search bounds by ATLAS. For a lightest NP fermion triplet with a maximal branching ratio to either electrons or muons, we exclude NP fermion masses of up to 650 GeV, while this bound is reduced to approximately 400 GeV in the tau-philic case. Allowing for a general flavor structure, we set limits on the Yukawa couplings, which are directly related to the neutrino flavor structure.

Inferring astrophysical information from gravitational waves emitted by compact binaries is one of the key science goals of gravitational-wave astronomy. In order to reach the full scientific potential of gravitational-wave experiments, we require techniques to mitigate the cost of Bayesian inference, especially as gravitational-wave signal models and analyses become increasingly sophisticated and detailed. Reduced-order models (ROMs) of gravitational waveforms can significantly reduce the computational cost of inference by removing redundant computations. In this paper, we construct the first reduced-order models of gravitational-wave signals that include the effects of spin precession, inspiral, merger, and ringdown in compact object binaries and that are valid for component masses describing binary neutron star, binary black hole, and mixed binary systems. This work utilizes the waveform model known as “IMRPhenomPv2.” Our ROM enables the use of a fast reduced-order quadrature (ROQ) integration rule which allows us to approximate Bayesian probability density functions at a greatly reduced computational cost. We find that the ROQ rule can be used to speed-up inference by factors as high as 300 without introducing systematic bias. This corresponds to a reduction in computational time from around half a year to half a day for the longest duration and lowest mass signals. The ROM and ROQ rules are available with the main inference library of the LIGO Scientific Collaboration, LALInference.

We study a coupled quintessence model with pure momentum exchange and present the effects of such an interaction on the cosmic microwave background (CMB) and matter power spectrum. For a wide range of negative values of the coupling parameter $\beta$ structure growth is suppressed and the model can reconcile the tension between cosmic microwave background observations and structure growth inferred from cluster counts. We find that this model is as good as $\mathrm{\Lambda }\mathrm{CDM}$ for CMB and baryon acoustic oscillation data, while the addition of cluster data makes the model strongly preferred, improving the best-fit ${\chi }^2$ value by more than 16.

The inclusion of dissipative effects in cosmic fluids modifies their clustering properties and could have observable effects on the formation of large-scale structures. We analyze the evolution of density perturbations of cold dark matter endowed with causal bulk viscosity. The perturbative analysis is carried out in the Newtonian approximation and the bulk viscosity is described by the causal Israel-Stewart (IS) theory. In contrast to the noncausal Eckart theory, we obtain a third-order evolution equation for the density contrast that depends on three free parameters. For certain parameter values, the density contrast and growth factor in IS mimic their behavior in $\mathrm{\Lambda }\mathrm{CDM}$ when $z\ge 1$. Interestingly, and contrary to intuition, certain sets of parameters lead to an increase of the clustering.

When comparing constraints on the weakly interacting massive particle (WIMP) properties from direct and indirect detection experiments it is crucial that the assumptions made about the dark matter (DM) distribution are realistic and consistent. For instance, if the Fermi-LAT Galactic center GeV gamma-ray excess was due to WIMP annihilation, its morphology would be incompatible with the standard halo model that is usually used to interpret data from direct detection experiments. In this article, we calculate exclusion limits from direct detection experiments using self-consistent velocity distributions, derived from mass models of the Milky Way where the DM halo has a generalized Navarro-Frenk-White profile. We use two different methods to make the mass model compatible with a DM interpretation of the Galactic center gamma-ray excess. First, we fix the inner slope of the DM density profile to the value that best fits the morphology of the excess. Second, we allow the inner slope to vary and include the morphology of the excess in the data sets used to constrain the gravitational potential of the Milky Way. The resulting direct detection limits differ significantly from those derived using the standard halo model, in particular for light WIMPs, due to the differences in both the local DM density and velocity distribution.

We perform a detailed study of the weak interactions of standard model neutrinos with the primordial plasma and their effect on the resonant production of sterile neutrino dark matter. Motivated by issues in cosmological structure formation on small scales, and reported x-ray signals that could be due to sterile neutrino decay, we consider 7 keV-scale sterile neutrinos. Oscillation-driven production of such sterile neutrinos occurs at temperatures $T\gtrsim 100\mathrm{MeV}$, where we study two significant effects of weakly charged species in the primordial plasma: (1) the redistribution of an input lepton asymmetry; (2) the opacity for active neutrinos. We calculate the redistribution analytically above and below the quark-hadron transition, and match with lattice QCD calculations through the transition. We estimate opacities due to tree-level processes involving leptons and quarks above the quark-hadron transition, and the most important mesons below the transition. We report final sterile neutrino dark matter phase space densities that are significantly influenced by these effects, and yet relatively robust to remaining uncertainties in the nature of the quark-hadron transition. We also provide transfer functions for cosmological density fluctuations with cutoffs at $k\simeq 10h{\mathrm{Mpc}}^{-1}$, that are relevant to galactic structure formation.

We report on a comprehensive all-sky search for periodic gravitational waves in the frequency band 100–1500 Hz and with a frequency time derivative in the range of $[-1.18,+1.00]\times 10^{-8}\mathrm{Hz}/\mathrm{s}$. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. This search uses the data from the initial LIGO sixth science run and covers a larger parameter space with respect to any past search. A Loosely Coherent detection pipeline was applied to follow up weak outliers in both Gaussian (95% recovery rate) and non-Gaussian (75% recovery rate) bands. No gravitational wave signals were observed, and upper limits were placed on their strength. Our smallest upper limit on worst-case (linearly polarized) strain amplitude $h_0$ is $9.7\times 10^{-25}$ near 169 Hz, while at the high end of our frequency range we achieve a worst-case upper limit of $5.5\times 10^{-24}$. Both cases refer to all sky locations and entire range of frequency derivative values.

We propose a novel experimental approach to explore exotic spin-dependent interactions using a spin-exchange relaxation-free (SERF) magnetometer, the most sensitive noncryogenic magnetic-field sensor. This approach studies the interactions between optically polarized electron spins located inside a vapor cell of the SERF magnetometer and unpolarized or polarized particles of external solid-state objects. The coupling of spin-dependent interactions to the polarized electron spins of the magnetometer induces the tilt of the electron spins, which can be detected with high sensitivity by a probe laser beam similarly as an external magnetic field. We estimate that by moving unpolarized or polarized objects next to the SERF Rb vapor cell, the experimental limit to the spin-dependent interactions can be significantly improved over existing experiments, and new limits on the coupling strengths can be set in the interaction range below ${10}^{-2}\mathrm{m}$.

We investigate the temperature dependence of the thermal dilepton rate and the electrical conductivity of the gluon plasma at temperatures of 1.1, 1.3, and $1.5T_c$ in quenched QCD. Making use of nonperturbatively clover-improved Wilson valence quarks allows for a clean extrapolation of the vector meson correlation function to the continuum limit. We found that the vector correlation function divided by $T^3$ is almost temperature independent in the current temperature window. The spectral functions are obtained by ${\chi }^2$ fitting of phenomenologically inspired Ansätze for the spectral function to the continuum extrapolated correlator data, where the correlations between the data points have been included. Systematic uncertainties arising from varying the Ansätze motivated from strong coupling theory as well as perturbation theory are discussed and estimated. We found that the electrical conductivity of the hot medium, related to the slope of the vector spectral function at zero frequency and momentum, is $0.2C_{em}\lesssim \sigma /T\lesssim 0.7C_{em}$ for $T=1.1T_c$ and $0.2C_{em}\lesssim \sigma /T\lesssim 0.4C_{em}$ for the higher temperatures. The dilepton rates and soft photon rates, resulting from the obtained spectral functions, show no significant temperature dependence, either.

We study inelastic meson-meson scattering that is governed by quark-antiquark annihilation and creation involving a quark and an antiquark annihilating into a gluon, and subsequently the gluon creating another quark-antiquark pair. The resultant hadronic reactions include for $I=1$: $\pi \pi \to \rho \rho$, $K\overline{K}\to K^{*}{\overline{K}}^{*}$, $K{\overline{K}}^{*}\to K^{*}{\overline{K}}^{*}$, $K^{*}\overline{K}\to K^{*}{\overline{K}}^{*}$, as well as $\pi \pi \to K\overline{K}$, $\pi \rho \to K{\overline{K}}^{*}$, $\pi \rho \to K^{*}\overline{K}$, and $K\overline{K}\to \rho \rho$. In each reaction, one or two Feynman diagrams are involved in the Born approximation. We derive formulas for the unpolarized cross section, the transition amplitude, and the transition potential for quark-antiquark annihilation and creation. The unpolarized cross sections for the reactions are calculated at six temperatures, and prominent temperature dependence is found. It is due to differences among mesonic temperature dependence in hadronic matter.

Besides the conventional strong and electromagnetic decay modes, the $J/\psi$ particle can also decay via the weak interaction in the standard model. In this paper, nonleptonic $J/\psi \to D_{s,d}\pi$, $D_{s,d}K$ weak decays, corresponding to the externally emitted virtual $W$ boson process, are investigated with the perturbative QCD approach. It is found that the branching ratio for the Cabibbo-favored $J/\psi \to D_s\pi$ decay can reach up to $\mathcal{O}({10}^{-10})$, which might be potentially measurable at the future high-luminosity experiments.

We report on the possibility of reweighting parton-shower Monte Carlo predictions for scale variations in the parton-shower algorithm. The method is based on a generalization of the Sudakov veto algorithm. We demonstrate the feasibility of this approach using example physical distributions. Implementations are available for both of the parton-shower modules in the Herwig 7 event generator.

We study a proposal for the resolution of the black hole information puzzle within the context of modified versions of quantum theory involving spontaneous reduction of the quantum state. The theories of this kind, which were developed in order to address the so-called measurement problem in quantum theory have, in the past, been framed in a nonrelativistic setting and in that form they were previously applied to the black hole information problem. Here, and for the first time, we show in a simple toy model, a treatment of the problem within a fully relativistic setting. We also discuss the issues that the present analysis leaves as open problems to be dealt with in future refinements of the present approach.

The fraction of the Universe going into primordial black holes (PBHs) with initial mass $M_{*}\approx 5\times 10^{14}\mathrm{g}$, such that they are evaporating at the present epoch, is strongly constrained by observations of both the extragalactic and Galactic $\gamma$-ray backgrounds. However, while the dominant contribution to the extragalactic background comes from the time-integrated emission of PBHs with initial mass $M_{*}$, the Galactic background is dominated by the instantaneous emission of those with initial mass slightly larger than $M_{*}$ and current mass below $M_{*}$. Also, the instantaneous emission of PBHs smaller than $0.4M_{*}$ mostly comprises secondary particles produced by the decay of directly emitted quark and gluon jets. These points were missed in the earlier analysis by Lehoucq et al. using EGRET data. For a monochromatic PBH mass function, with initial mass $(1+\mu )M_{*}$ and $\mu \ll 1$, the current mass is $(3\mu {)}^{1/3}{M}_{*}$, and the Galactic background constrains the fraction of the Universe going into PBHs as a function of $\mu$. However, the initial mass function cannot be precisely monochromatic, and even a tiny spread of mass around $M_{*}$ would generate a current low-mass tail of PBHs below $M_{*}$. This tail would be the main contributor to the Galactic background, so we consider its form and the associated constraints for a variety of scenarios with both extended and nearly monochromatic initial mass functions. In particular, we consider a scenario in which the PBHs form from critical collapse and have a mass function which peaks well above $M_{*}$. In this case, the largest PBHs could provide the dark matter without the $M_{*}$ ones exceeding the $\gamma$-ray background limits.