Cosmic background neutrinos have a large velocity dispersion, which causes the evolution of long-wavelength density perturbations to depend on scale. This scale-dependent growth leads to the well-known suppression in the linear theory matter power spectrum that is used to probe neutrino mass. In this paper, we study the impact of long-wavelength density perturbations on small-scale structure formation. By performing separate universe simulations where the long-wavelength mode is absorbed into the local expansion, we measure the responses of the cold dark matter (CDM) power spectrum and halo mass function, which correspond to the squeezed-limit bispectrum and halo bias. We find that the scale-dependent evolution of the long-wavelength modes causes these quantities to depend on scale and provide simple expressions to model them in terms of scale and the amount of massive neutrinos. Importantly, this scale-dependent bias reduces the suppression in the linear halo power spectrum due to massive neutrinos by 13% and 26% for objects of bias $\overline{b}=2$ and $\overline{b}\gg 1$, respectively. We demonstrate with high statistical significance that the scale-dependent halo bias cannot be modeled by the CDM and neutrino density transfer functions at the time when the halos are identified. This reinforces the importance of the temporal nonlocality of structure formation, especially when the growth is scale dependent.

It has recently been claimed, with a $4.2\sigma$ significance level, that gravitational wave echoes at a frequency of about 72 Hz have been produced in the GW170817 event. The merging of compact stars can lead to the emission of gravitational wave echoes if the postmerger object features a photon sphere capable of partially trapping the gravitational waves. If the postmerger source is a black hole, a second internal reflection surface, associated with quantum effects near the black hole horizon, must be present to avoid the gravitational wave capture. Alternatively, gravitational wave echoes can be produced by ultracompact stars crossing the photon-sphere line in the mass-radius diagram during the neutron star merging. In this case, the second reflection surface is not needed. A recently proposed preliminary analysis using an incompressible (and so unphysical) equation of state suggests that gravitational wave echoes at a frequency of tens of hertz can be produced by an ultracompact star. Since strange stars are extremely compact, we examine the possibility that strange stars emit gravitational wave echoes at such a frequency. Using parametrized models of the equation of state of ultrastiff quark matter we find that a strange star can emit gravitational wave echoes, but the corresponding frequencies are on the order of tens of hilohertz, and thus not compatible with the 72 Hz signal.

In this paper, we study the lepton number violation processes of $B_c$ meson induced by possible doubly-charged scalars. Both the three-body decay channels and the four-body decay channels are considered. For the former, the $B_c^{-}\to D_s^{+}{\mu }^{-}{\mu }^{-}$ channel has the largest branching fraction $9.19\times {10}^{-23}$, and for the later channels, the $B_c^{-}\to {\overline{B}}_s^0{\pi }^{+}{\mu }^{-}{\mu }^{-}$ channel has the largest branching ratio $1.03\times {10}^{-27}$. These results are too small to be within the current experimental precision. However, they can provide a comparison in theory with the similar cases involving an off-shell Majorana neutrino.

We study $CPT$ and Lorentz violation in the tau-lepton sector of the Standard Model in the context of the Standard-Model Extension, parametrized by a coefficient which is thus far unbounded by experiment. We show that any nonzero value of this coefficient implies that, for sufficiently large energies, Standard Model fermions become unstable against decay due to the emission of a pair of tau-antitau leptons. We calculate the induced fermion energy-loss rate and we deduce the first limit on the Lorentz- and $CPT$-violation coefficient.

We interpret the physical symmetry preserving the lepton number as a shadow of a finite pseudo-Riemannian structure of the standard model. Using the pseudo-Riemannian generalizations of real spectral triples we describe the geometries with indefinite metric over finite-dimensional algebras and their Riemannian shadows. We apply the discussion to the standard model spectral triple, and classify possible time orientations leading to restrictions on the physical parameters and symmetries.

The cross section of associated production of a $Z$ boson with heavy flavor jets in $pp$ collisions is calculated using the Sherpa Monte Carlo generator and the analytical combined QCD approach based on $k_{\mathrm{T}}$ factorization at small $x$ and conventional collinear QCD at large $x$. A satisfactory description of the ATLAS and CMS data on the $p_{\mathrm{T}}$ spectra of $Z$ bosons and $c$ jets in the whole rapidity, $y$, region is shown. Searching for the intrinsic charm (IC) contribution in these processes, which could be visible at large $y>1.5$, we study observables very sensitive to nonzero IC contributions and less affected by theoretical QCD scale uncertainties. One of such observables is the so-called double ratio, the ratio of the differential cross section of $Z+c$ production in the central region of $|y|<1.5$ and in the forward region $1.5<|y|<2.5$, divided by the same ratio for $Z+b$ production. These observables could be more promising for the search of IC at LHC as compared to the observables considered earlier.

We calculate the production of pairs of ${\chi }_{cJ}$ mesons with all possible combinations of $J=0$, 1, 2. The production mechanism which we consider is the crossed-channel gluon exchange in the gluon-gluon fusion reaction, the mechanism relevant for large rapidity separations between ${\chi }_c$ mesons. The salient features of the $t$ and $u$-channel gluon exchange are the broad distributions in rapidity difference $\mathrm{\Delta }y$ between ${\chi }_c$ mesons. The building blocks are the vertices $g^{*}{g}^{*}\to {\chi }_{cJ}$ for off-shell gluons. We stick to the color-singlet model and calculate the gluon fusion vertices in the limit of heavy quarks with nonrelativistic motion in the bound state. These vertices are used to construct the $g^{*}{g}^{*}\to {\chi }_{c{J}_1}{\chi }_{c{J}_2}$ amplitudes. We then calculate hadron-level cross sections using the $k_T$-factorization approach. Several differential distributions at the $pp$ center of mass energy $\sqrt{s}=8\mathrm{TeV}$ are shown. We briefly discuss the contribution to $J/\psi J/\psi$ production at large rapidity separation. For reference we show some distributions for production of ${\chi }_{c{J}_1}{\chi }_{c{J}_2}$ pairs in double parton scattering. The discussed single parton scattering mechanisms yield similar shapes of different distributions as the double parton scattering mechanisms.

The possibility of time travel is explored within the framework of first order gravity theory in vacuum. We present explicit solutions (to the field equations), whose geodesics allow the proper clock to run backwards. These four-geometries contain degenerate as well as nondegenerate tetrad fields that are sewn together continuously over different regions of the spacetime. Being devoid of matter and also of torsion by construction, these solutions have no exotic field content.

Recent detections of merging black holes allow observational tests of the nature of these objects. In some proposed models, nontrivial structure at or near the black hole horizon could lead to echo signals in gravitational wave data. Recently, Abedi-Dykaar-Afshordi (ADA) claimed tentative evidence for repeating damped echo signals following the gravitational-wave signals of the binary black hole merger events recorded in the first observational period of the Advanced LIGO interferometers. We reanalyze the same data, addressing some of the shortcomings of their method using more background data and a modified procedure. We find a reduced statistical significance for the claims of evidence for echoes, calculating increased p-values for the null hypothesis of echo-free noise. The reduced significance is entirely consistent with noise, and so we conclude that the analysis of Abedi et al. does not provide any observational evidence for the existence of Planck-scale structure at black hole horizons.

Motivated by the desire for highly accurate numerical computations of compact binary spacetimes in the era of gravitational wave astronomy, we reexamine hyperbolicity and well-posedness of the initial value problem for popular models of general relativistic fluids. Our analysis relies heavily on the dual-frame formalism, which allows us to work in the Lagrangian frame, where computation is relatively easy, before transforming to the desired Eulerian form. This general strategy allows for the construction of compact expressions for the characteristic variables in a highly economical manner. General relativistic hydrodynamics, ideal magnetohydrodynamics, and resistive magnetohydrodynamics are considered in turn. In the first case, we obtain a simplified form of earlier expressions. In the second, we show that the flux-balance law formulation used in typical numerical applications is only weakly hyperbolic and thus does not have a well-posed initial value problem. Newtonian ideal magnetohydrodynamics is found to suffer from the same problem when written in flux-balance law form. An alternative formulation, closely related to that of Anile and Pennisi, is instead shown to be strongly hyperbolic. In the final case, we find that the standard forms of resistive magnetohydrodynamics, relying upon a particular choice of “generalized Ohm’s law,” are only weakly hyperbolic. The latter problem may be rectified by adjusting the choice of Ohm’s law, but we do not do so here. Along the way, weak hyperbolicity of the field equations for dust and charged dust is also observed. More sophisticated systems, such as multifluid and elastic models, are also expected to be amenable to our treatment.

Recent TeV observations of nearby pulsars with the HAWC telescope have been interpreted as evidence that the diffusion of high-energy electrons and positrons within pulsar wind nebulae is highly inefficient compared to the rest of the interstellar medium. If the diffusion coefficient well outside the nebula is close to the value inferred for the region inside the nebula, high-energy electrons and positrons produced by the two observed pulsars could not contribute significantly to the local measured cosmic-ray flux. The HAWC Collaboration thus concluded that, under the assumption of isotropic and homogeneous diffusion, the two pulsars are ruled out as sources of the anomalous high-energy positron flux. Here, we argue that since the diffusion coefficient is likely not spatially homogeneous, the assumption leading to this conclusion is flawed. We solve the diffusion equation with a radially dependent diffusion coefficient, and show that the pulsars observed by HAWC produce potentially perfect matches to the observed high-energy positron fluxes. We also study the implications of inefficient diffusion within pulsar wind nebulae on Galactic scales, and show that cosmic rays are likely to have very long residence times in regions of inefficient diffusion. We describe how this prediction can be tested with studies of the diffuse Galactic emission.

The study of the Higgs boson properties is one of the most relevant activities in current particle physics. In particular, the Higgs boson couplings to third generation fermions is an important test of the mechanism of mass generation. In spite of their impact on the production and decay properties of the Higgs boson, the values of these couplings are still uncertain and, in models of new physics, they can differ in magnitude as well as in sign with respect to the Standard Model case. In this article, we study the possibility of a wrong sign bottom-quark Yukawa coupling within the framework of the minimal (MSSM) and next-to-minimal (NMSSM) supersymmetric Standard Model. We find that a wrong sign regime is not possible in the MSSM without violating experimental constraints, and we numerically examine the parameter values which give a wrong sign bottom Yukawa within the NMSSM. Possible experimental tests are also discussed, including novel decays of the heavy $CP$-even and $CP$-odd Higgs fields that may be probed in the near future and that may lead to an explanation of some intriguing di-boson signatures observed at the ATLAS experiment.

We study and compare various $Z^{\prime }$ models arising from $SO(10)$, focusing in particular on the Abelian subgroup $U(1{)}_R\times U(1{)}_{B-L}$, broken at the TeV scale to Standard Model hypercharge $U(1{)}_Y$. The gauge group $U(1{)}_R\times U(1{)}_{B-L}$, which is equivalent to the $U(1{)}_Y\times U(1{)}_{\chi }$ in a different basis, is well motivated from $SO(10)$ breaking and allows neutrino mass via the linear seesaw mechanism. Assuming supersymmetry, we first consider single step gauge unification to predict the gauge couplings, then we consider the detection and characterization prospects of the resulting $Z^{\prime }$ at the LHC by studying its possible decay modes into di-leptons as well as into Higgs bosons. The main new result here is to analyse in detail the expected leptonic forward-backward asymmetry at the high luminosity LHC and show that it may be used to discriminate the $U(1{)}_R\times U(1{)}_{B-L}$ model from the usual $B-L$ model based on $U(1{)}_Y\times U(1{)}_{B-L}$.

We study the discovery reach of future Dark Matter (DM) Direct Detection experiments using DM-electron scattering in the presence of the solar neutrino background. At these low energies traditional methods for nuclear and electronic recoil discrimination fail, implying that the neutrino- nucleus scattering background can be sizable. We calculate discovery limits based on ionization values of signal and background, and quantify the dependence on the ionization model. Moreover, we explore how the dependence of the DM cross section discovery limits varies with exposure, electronic/nuclear recoil discrimination, DM form factors, and DM astrophysical uncertainties.

The three-particle quantization condition is partially diagonalized in the center-of-mass frame by using cubic symmetry on the lattice. To this end, instead of spherical harmonics, the kernel of the Bethe-Salpeter equation for particle-dimer scattering is expanded in the basis functions of different irreducible representations of the octahedral group. Such a projection is of particular importance for the three-body problem in the finite volume due to the occurrence of three-body singularities above breakup. Additionally, we study the numerical solution and properties of such a projected quantization condition in a simple model. It is shown that, for large volumes, these solutions allow for an instructive interpretation of the energy eigenvalues in terms of bound and scattering states.

Coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$) can be used to determine the neutron part of nuclear form factors, unlocking intrinsic properties of nuclear structure. In contrast with other such methods, $\mathrm{CE}\nu \mathrm{NS}$ is free from both strong interaction effects and Coulomb distortions. We propose precision measurements of $\mathrm{CE}\nu \mathrm{NS}$ with an upcoming accelerator facility and determine the corresponding requirements for such a neutrino detector. We find that most significant backgrounds come from fast neutrons, induced by cosmogenic muons or from the pion decays at rest in the target station. With ton-scale liquid noble gas detectors, we will not only achieve percent-level precision in the measurement of neutron radii but also clarify contributions of higher-order moments to nuclear form factors.

Differential and double-differential cross sections for the production of top quark pairs in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ are measured as a function of kinematic variables of the top quarks and the top quark-antiquark ($t\overline{t}$) system. In addition, kinematic variables and multiplicities of jets associated with the $t\overline{t}$ production are measured. This analysis is based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of $35.8{\mathrm{fb}}^{-1}$. The measurements are performed in the $\mathrm{lepton}+\text{jets}$ decay channels with a single muon or electron and jets in the final state. The differential cross sections are presented at the particle level, within a phase space close to the experimental acceptance, and at the parton level in the full phase space. The results are compared to several standard model predictions that use different methods and approximations. The kinematic variables of the top quarks and the $t\overline{t}$ system are reasonably described in general, though none predict all the measured distributions. In particular, the transverse momentum distribution of the top quarks is more steeply falling than predicted. The kinematic distributions and multiplicities of jets are adequately modeled by certain combinations of next-to-leading-order calculations and parton shower models.