By absorbing fluctuations into a local background, separate universe simulations provide a powerful technique to characterize the response of small-scale observables to the long-wavelength density fluctuations, for example those of the power spectrum and halo mass function which lead to the squeezed-limit $n$-point function and halo bias, respectively. Using quintessence dark energy as the paradigmatic example, we extend these simulation techniques to cases where non-gravitational forces in other sectors establish a Jeans scale across which the growth of density fluctuations becomes scale dependent. By characterizing the separate universes with matching background expansion histories, we show that the power spectrum and mass function responses depend on whether the long-wavelength mode is above or below the Jeans scale. Correspondingly, the squeezed bispectrum and halo bias also become scale dependent. Models of bias that are effectively local in the density field at a single epoch, initial or observed, cannot describe this effect which highlights the importance of temporal nonlocality in structure formation. Validated by these quintessence tests, our techniques are applicable to a wide range of models where the complex dynamics of additional fields affect the clustering of matter in the linear regime and it would otherwise be difficult to simulate their impact in the nonlinear regime.

General features of spontaneous baryogenesis are studied. The relation between the time derivative of the (pseudo) Goldstone field and the baryonic chemical potential is revisited. It is shown that this relation essentially depends upon the representation chosen for the fermionic fields with nonzero baryonic number (quarks). The calculations of the cosmological baryon asymmetry are based on the kinetic equation generalized to the case of nonstationary background. The effects of the finite interval of the integration over time are also taken into consideration. All these effects combined lead to a noticeable deviation of the magnitude of the baryon asymmetry from the canonical results.

Neutrino oscillations are a widely observed and well-established phenomenon. It is also well known that deviations with respect to flavor conversion probabilities in vacuum arise due to neutrino interactions with matter. In this work, we analyze the impact of new interactions between neutrinos and the dark matter present in the Milky Way on the neutrino oscillation pattern. The dark matter-neutrino interaction is modeled by using an effective coupling proportional to the Fermi constant $G_F$ with no further restrictions on its flavor structure. For the galactic dark matter profile we consider a homogeneous distribution as well as several density profiles, estimating in all cases the size of the interaction required to get an observable effect at different neutrino energies. Our discussion is mainly focused in the PeV neutrino energy range, to be explored in observatories like IceCube and KM3NeT. The obtained results may be interpreted in terms of a light $\mathcal{O}(\mathrm{sub}\text{−}\mathrm{eV}–\mathrm{keV})$ or weakly interacting massive particlelike dark matter particle or as a new interaction with a mediator of $\mathcal{O}(\mathrm{sub}\text{−}\mathrm{eV}–\mathrm{keV})$ mass.

The anarchy principle leading to the seesaw ensemble is studied analytically with the usual tools of random matrix theory. The probability density function for the seesaw ensemble of $N\times N$ matrices is obtained in terms of a multidimensional integral. This integral involves all light neutrino masses, leading to a complicated probability density function. It is shown that the probability density function for the neutrino mixing angles and phases is the appropriate Haar measure. The decoupling of the light neutrino masses and neutrino mixings implies no correlation between the neutrino mass eigenstates and the neutrino mixing matrix and leads to a loss of predictive power when comparing with observations. This decoupling is in agreement with some of the claims found in the literature.

Different models based on the extended $SU(3{)}_C\times SU(3{)}_L\times U(1{)}_X$ (331) gauge group have been proposed over the past four decades. Yet, despite being an active research topic, the status of lepton number in 331 models has not been fully addressed in the literature, and furthermore many of the original proposals can not explain the observed neutrino masses. In this paper we review the basic features of various 331 models, focusing on potential sources of lepton number violation. We then describe different modifications which can be made to the original models in order to accommodate neutrino (and charged lepton) masses.

For the general two-Higgs-doublet model, we present conditions for having spontaneous $CP$ violation, in terms of physical masses and couplings. These relations involve the charged Higgs mass, its cubic couplings with neutral scalars and quartic coupling, and become particularly simple in the alignment limit. In the simplified model with softly broken ${\mathcal{Z}}_2$ symmetry, some deviation from alignment is required for spontaneous $CP$ violation to be present.

Many new physics models contain a neutral scalar resonance that can be predominantly produced via gluon fusion through loops. In such a case, there could be important effects of additional particles, that in turn may hadronize before decaying and form bound states. This interesting possibility may lead to novel signatures with double peaks that can be searched for at the LHC. We study the phenomenology of double peak searches in diboson final states from loop-induced production and decay of a new neutral spin-0 resonance at the LHC. The loop-induced couplings should be mediated by particles carrying color and electroweak charge that after forming bound states will induce a second peak in the diboson invariant mass spectrum near twice their mass. A second peak could be present via loop-induced couplings into $gg$ (dijet), $\gamma \gamma$ and $Z\gamma$ final states as well as in the $WW$ and $ZZ$ channels for the case of a pseudoscalar resonance or for scalars with suppressed tree-level coupling to gauge bosons.

The large $N_c$ limit provides relations that can be used to calculate the ${\gamma }^{*}N\to \mathrm{\Delta }(1232)$ quadrupole form factors at low and intermediate $Q^2$ under the assumption of the pion cloud dominance. There are two limitations in those parametrizations. First, the parametrization of the Coulomb quadrupole form factor underestimate the low $Q^2$ data. Second, when extrapolated for the timelike region, the form factors violate Siegert’s theorem by terms of the order $1/N_c^2$. We propose here corrections to the parametrization of the electric quadrupole form factor, which violate Siegert’s theorem only by terms of the order $1/N_c^4$. Combining the improved large $N_c$ pion cloud parametrizations with the valence quark contributions based on a covariant quark model for the quadrupole transition form factors, we obtain an extrapolation to the timelike region consistent with Siegert’s theorem, and accomplish also a very good description of the data.

We analyze a $37{\mathrm{pb}}^{-1}$ data sample collected with the SND detector at the VEPP-2000 $e^{+}{e}^{-}$ collider in the center-of-mass energy range 1.05–2.00 GeV and present an updated measurement of the $e^{+}{e}^{-}\to \omega {\pi }^0\to {\pi }^0{\pi }^0\gamma$ cross section. In particular, we correct the mistake in radiative correction calculation made in our previous measurement based on a part of the data. The measured cross section is fitted with the vector meson dominance model with three $\rho$-like states and used to test the conserved vector current hypothesis in the ${\tau }^{-}\to \omega {\pi }^{-}{\nu }_{\tau }$ decay.

We study the quantum mechanics of self-gravitating thin shell collapse by solving the polymerized Wheeler-DeWitt equation. We obtain the energy spectrum and solve the time-dependent equation using numerics. In contradistinction to the continuum theory, we are able to consistently quantize the theory for super-Planckian black holes, and find two choices of boundary conditions which conserve energy and probability, as opposed to one in the continuum theory. Another feature unique to the polymer theory is the existence of negative energy stationary states that disappear from the spectrum as the polymer scale goes to 0. In both theories the probability density is positive semidefinite only for the space of positive energy stationary states. Dynamically, we find that an initial Gaussian probability density develops regions of negative probability as the wave packet approaches $R=0$ and bounces. This implies that the bouncing state is a sum of both positive and negative eigenstates.

We apply the technique of the spinfoam to study space-time, which, classically, contains a curvature singularity. We derive from the full covariant loop quantum gravity (LQG) that the region near curvature singularity has to be of the strong quantum gravity effect. We show that the spinfoam configuration describing the near-singularity region has to be of small spins $j$, in order that its contribution to the full spinfoam amplitude is nontrivial. The spinfoams in low and high-curvature regions of space-time may be viewed as in two different phases of covariant LQG. There should be a phase transition as space-time described by the spinfoam becomes more and more curved. A candidate of the order parameter is proposed for understanding the phase transition. Moreover, we also analyze the spin-spin correlation function of the spinfoam and show the correlation is of long range in the low-curvature phase. This work is a first step toward understanding the physics of black hole and early Universe from the full covariant LQG theory.

In this paper, we examine the behavior of modes of the Kerr geometry when the mode’s frequency is purely imaginary. We demonstrate that quasinormal modes must be polynomial in nature if their frequency is purely imaginary, and present a method for computing such modes. The nature of these modes, however, is not always easy to determine. Some of the polynomial modes we compute are quasinormal modes. However, some are simultaneously quasinormal modes and total transmission modes, while others fail to satisfy the requisite boundary conditions for either. This analysis is, in part, an extension of the results known for Schwarzschild black holes, but clarifies misconceptions for the behavior of modes when the black hole has angular momentum. We also show that the algebraically special modes of Kerr with $m=0$ have an additional branch of solutions not seen before in the literature. All of these results are in precise agreement with new numerical solutions for sequences of gravitational quasinormal modes of Kerr spacetime. However, we show that some prior numerical and analytic results concerning the existence of quasinormal modes of Kerr with purely imaginary frequencies were incorrect.

It is proved that spherically symmetric compact reflecting objects cannot support static bound-state configurations made of scalar fields whose self-interaction potential $V({\psi }^2)$ is a monotonically increasing function of its argument. Our theorem rules out, in particular, the existence of massive scalar hair outside the surface of a spherically symmetric compact reflecting star.

Observations by the Fermi-LAT have uncovered a bright, spherically symmetric excess surrounding the center of the Milky Way Galaxy. The spectrum of the $\gamma$-ray excess peaks sharply at an energy $\sim 2\mathrm{GeV}$, exhibiting a hard spectrum at lower energies, and falls off quickly above an energy $\sim 5\mathrm{GeV}$. The spectrum of the excess above $\sim 10\mathrm{GeV}$ is potentially an important discriminator between different physical models for its origin. We focus our study on observations of the $\gamma$-ray excess at energies exceeding 10 GeV, finding: (1) a statistically significant excess remains in the energy range 9.5–47.5 GeV, which is not degenerate with known diffuse emission templates such as the Fermi bubbles, (2) the radial profile of the excess at high energies remains relatively consistent with data near the spectral peak (3) the data above $\sim 5\mathrm{GeV}$ prefer a slightly greater ellipticity with a major axis oriented perpendicular to the Galactic plane. Using the recently developed non-Poissonian template fit, we find mild evidence for a point-source origin for the high-energy excess, although given the statistical and systematic uncertainties we show that a smooth origin of the high-energy emission cannot be ruled out. We discuss the implication of these findings for pulsar and dark matter models of the $\gamma$-ray excess. Finally we provide a number of updated measurements of the $\gamma$-ray excess, utilizing novel diffuse templates and the Pass 8 data set.

We study the decay mode of the $a_1(1260)$ into a ${\pi }^{+}$ in $p$ wave and the $f_0(980)$ that decays into ${\pi }^{+}{\pi }^{-}$ in $s$ wave. The mechanism proceeds via a triangular mechanism where the $a_1(1260)$ decays into $K^{*}\overline{K}$, the $K^{*}$ decays to an external ${\pi }^{+}$ and an internal $K$ that fuses with the $\overline{K}$ producing the $f_0(980)$ resonance. The mechanism develops a singularity at a mass of the $a_1(1260)$ around 1420 MeV, producing a peak in the cross section of the $\pi p$ reaction, used to generate the mesonic final state, which provides a natural explanation of all the features observed in the COMPASS experiment, where a peak observed at this energy is tentatively associated to a new resonance called $a_1(1420)$. On the other hand, the triangular singularity studied here gives rise to a remarkable feature, where a peak is seen for a certain decay channel of a resonance at an energy about 200 MeV higher than its nominal mass.

In this article, we focus on new scalar $\varphi$ mediated scalar/vectorial weakly interacting massive particles (WIMPs) with $\varphi$’s mass slightly below the WIMP mass. To explain the Galactic center 1–3 GeV gamma-ray excess, here we consider the case that a WIMP pair predominantly annihilates into an on-shell $\varphi \varphi$ pair with $\varphi$ mainly decaying to $\tau \overline{\tau }$. The masses of WIMPs are in a range about 14–22 GeV, and the annihilations of WIMPs are phase space suppressed today. In this annihilation scheme, the couplings of the $\varphi$-standard model (SM) particles are almost arbitrarily small, and the WIMP-nucleus spin-independent scattering can be tolerant by the present dark matter (DM) direct detections. A scalar mediator-Higgs field mixing is introduced, which is small and available. The lower limit on the couplings of the $\varphi$-SM particles set by the thermal equilibrium in the early Universe is derived, and this constraint is above the neutrino background for scalar DM in direct detections. The WIMPs may be detectable at the upgraded DM direct detection experiment in the next few years, and the exotic decay $h\to \varphi \varphi$, the production of $\varphi$ may be observable at the future high-luminosity $e^{+}{e}^{-}$ collider.

Identifying signatures of dark matter at indirect-detection experiments is generally more challenging for scenarios involving nonminimal dark sectors such as Dynamical Dark Matter (DDM) than for scenarios involving a single dark particle. This additional difficulty arises because the partitioning of the total dark-matter abundance across an ensemble of different constituent particles with different masses tends to “smear” the injection spectra of photons and other cosmic-ray particles that are produced via dark-matter annihilation or decay. As a result, the imprints of the dark sector on these cosmic-ray flux spectra typically take the form of continuum features rather than sharp peaks or lines. In this paper, however, we identify an unambiguous signature of nonminimal dark sectors such as DDM which can overcome these issues and potentially be observed at gamma-ray telescopes operating in the MeV range. We discuss the specific situations in which this signature can arise, and demonstrate that this signature can be exploited in order to significantly enhance our ability to resolve the unique spectral features of DDM and other nonminimal dark sectors at future gamma-ray facilities.

Several experiments reported hints for the violation of lepton flavor or lepton flavor universality in processes involving muons. Most prominently, there is the hint for a nonzero rate of the flavor violating Higgs decay $h\to \tau \mu$ at the LHC, as well as the hint for lepton flavor universality violation in rare $B$ meson decays at the LHCb. In addition, also the long-standing discrepancy in the anomalous magnetic moment of the muon motivates new physics connected to muons. A symmetry which violates lepton flavor universality is $L_{\mu }-L_{\tau }$: the difference of muon number and tau number. We show that adding vectorlike fermions to a $L_{\mu }-L_{\tau }$ theory generates naturally an effect in the anomalous magnetic moment of the muon and $h\to \tau \mu$, while effects in other $\tau \to \mu$ transitions are systematically suppressed by symmetry arguments. We find that if $L_{\mu }-L_{\tau }$ is gauged it is possible to also accommodate the discrepant $b\to s\mu \mu$ data while predicting a $\tau \to 3\mu$ and a modified $h\to \mu \mu$ rate within reach of upcoming experiments.