Cosmic-ray protons with energies above ${10}^{16}\mathrm{eV}$ passing near the Sun may interact with photons emitted by the Sun and be excited to a ${\Delta }^{+}$ resonance. When the ${\Delta }^{+}$ decays, it produces pions which further decay to muons and photons which may be detected with terrestrial detectors. A flux of muons, photon pairs (from ${\pi }^0$ decay), or individual high energy photons coming from near the Sun would be a rather striking signature, and the flux of these particles is a fairly direct measure of the flux of cosmic-ray nucleons, independent of the cosmic-ray composition. In a solid angle within 15° around the Sun, the flux of photon pairs is about $1.3\times {10}^{-3}\mathrm{\text{particles}}/({\mathrm{km}}^2·\mathrm{yr})$, while the flux of muons is about $0.33\times {10}^{-3}\mathrm{\text{particles}}/({\mathrm{km}}^2·\mathrm{yr})$. This is beyond the reach of current detectors like the Telescope Array, Auger, KASCADE-Grande, or IceCube. However, the muon flux might be detectable by next-generation air-shower arrays or neutrino detectors such as ARIANNA or ARA. We discuss the experimental prospects in some detail. Other cosmic-ray interactions occurring close to the Sun are also briefly discussed.

An alternative to the effective field theory approach to treat ghosts in higher derivative theories is to attempt to integrate them out via the Euclidean path integral formalism. It has been suggested that this method could provide a consistent framework within which we might tolerate the ghost degrees of freedom that plague, among other theories, the higher derivative gravity models that have been proposed to explain cosmic acceleration. We consider the extension of this idea to treating a class of terms with order six derivatives, and find that for a general term the Euclidean path integral approach works in the most trivial background, Minkowski. Moreover we see that even in de Sitter background, despite some difficulties, it is possible to define a probability distribution for tensorial perturbations of the metric.

Coincident observations with gravitational wave (GW) detectors and other astronomical instruments are among the main objectives of the experiments with the network of LIGO, Virgo, and GEO detectors. They will become a necessary part of the future GW astronomy as the next generation of advanced detectors comes online. The success of such joint observations directly depends on the source localization capabilities of the GW detectors. In this paper we present studies of the sky localization of transient GW sources with the future advanced detector networks and describe their fundamental properties. By reconstructing sky coordinates of ad hoc signals injected into simulated detector noise, we study the accuracy of the source localization and its dependence on the strength of injected signals, waveforms, and network configurations.

Jets plus missing transverse energy is one of the main search channels for new physics at the LHC. A major limitation lies in our understanding of QCD backgrounds. Using jet merging, we can describe the number of jets in typical background channels in terms of a staircase scaling, including theory uncertainties. The scaling parameter depends on the particles in the final state and on cuts applied. Measuring the staircase scaling will allow us to also predict the effective mass for standard model backgrounds. Based on both observables, we propose an analysis strategy avoiding model-specific cuts, which returns information about the color charge and the mass scale of the underlying new physics.

We study the implementation of global $SO(4)\sim SU(2{)}_L\otimes SU(2{)}_R$ symmetry in general potentials with $N$-Higgs-doublets in order to obtain models with custodial $SO(3{)}_C$ symmetry. We conclude that any implementation of the custodial $SO(4)$ symmetry is equivalent, by a basis transformation, to a canonical one if $SU(2{)}_L$ is the gauge factor, $U(1{)}_Y$ is embedded in $SU(2{)}_R$, and we require $N$ copies of the doublet representation of $SU(2{)}_R$. The invariance by $SO(4)$ automatically leads to a $CP$-invariant potential and the basis of the canonical implementation of $SO(4)$ is aligned to a basis where $CP$ symmetry acts in the standard fashion. We show different but equivalent implementations for the 2-Higgs-doublets model, including an implementation not previously considered.

We calculate the probability distributions of quarks in the ground state of the proton, and how they are affected in the presence of a constant background magnetic field. We focus on wave functions in the Landau and Coulomb gauges. We observe the formation of a scalar $u\mathrm{\text{−}}d$ diquark clustering. The overall distortion of the quark probability distribution under a very large magnetic field, as demanded by the quantization conditions on the field, is quite small. The effect is to elongate the distributions along the external field axis while localizing the remainder of the distribution.

It has been recently shown that puzzling excess events observed by the LSND and MiniBooNE neutrino experiments could be interpreted as a signal from the radiative decay of a heavy sterile neutrino (${\nu }_h$) of the mass from 40 to 80 MeV, with a muonic mixing strength $|U_{\mu h}{|}^2\simeq {10}^{-3}–{10}^{-2}$, and the lifetime ${10}^{-11}\lesssim {\tau }_h\lesssim {10}^{-9}$ s. We discuss bounds on $|U_{\mu h}{|}^2$ obtained from the recent precision measurements with muons and show that they are consistent with the above limits. If the ${\nu }_h$ exists its admixture in the ordinary muon or kaon decay would result in the decay chain $\mu \to e{\nu }_e{\nu }_h\to e{\nu }_e\gamma \nu$ or $K\to \mu {\nu }_h\to \mu \gamma \nu$, respectively. We propose a new experiment for a sensitive search for these processes in $\mu$ and $K$ decays at rest allowing to either definitively confirm or exclude the existence of the ${\nu }_h$. To our knowledge, no experiment has specifically searched for the signature of radiative decay of massive neutrinos from particle decays as proposed in this work. The search is complementary to the current experimental efforts to clarify the origin of the LSND and MiniBooNE anomalies.

In a consistent heterotic string theory, the Kalb-Ramond field, which is the source of space-time torsion, is augmented by Yang-Mills and gravitational Chern-Simons terms. When compactified to 4 dimensions and in the field theory limit, such additional terms give rise to interactions with interesting astrophysical predictions like rotation of plane of polarization for electromagnetic and gravitational waves. On the other hand, if one is also interested in coupling 2- or 3-form (Abelian or non-Abelian) gauge fields to torsion, one needs another class of interaction. In this paper, we shall study this interaction and offer some astrophysical and cosmological predictions. We explicitly calculate the Coleman-Weinberg potential for this theory. We also comment on the possibility of such terms in loop quantum gravity where, if the Barbero-Immirzi parameter is promoted to a field, acts as a source for torsion.

If the fundamental mass scale of superstring theory is as low as a few TeVs, the massive modes of vibrating strings, Regge excitations, will be copiously produced at the Large Hadron Collider (LHC). We discuss the complementary signals of low-mass superstrings at the proposed electron-positron facility (CLIC), in $e^{+}{e}^{-}$ and $\gamma \gamma$ collisions. We examine all relevant four-particle amplitudes evaluated at the center-of-mass energies near the mass of lightest Regge excitations and extract the corresponding pole terms. The Regge poles of all four-point amplitudes, in particular, the spin content of the resonances, are completely model-independent, universal properties of the entire landscape of string compactifications. We show that $\gamma \gamma \to e^{+}{e}^{-}$ scattering proceeds only through a spin-2 Regge state. We estimate that for this particular channel, string scales as high as 4 TeV can be discovered at the $11\sigma$ level with the first ${\mathrm{fb}}^{-1}$ of data collected at a center-of-mass energy $\approx 5\mathrm{TeV}$. We also show that for $e^{+}{e}^{-}$ annihilation into fermion-antifermion pairs, string theory predicts the precise value, equal to $1/3$, of the relative weight of spin 2 and spin 1 contributions. This yields a dimuon angular distribution with a pronounced forward-backward asymmetry, which will help distinguishing between low-mass strings and other beyond the standard model scenarios.

We study the small-mass limit of the one-loop spinor effective action, comparing the derivative expansion approximation with exact numerical results that are obtained from an extension to spinor theories of the partial-wave cutoff method. In this approach, one can compute numerically the renormalized one-loop effective action for radially separable gauge field background fields in spinor QED. We highlight an important difference between the small-mass limit of the derivative expansion for spinor and scalar theories.

The quadratically divergent scalar mass is subtractively renormalized unlike other divergences which are multiplicatively renormalized. We reexamine some technical aspects of the subtractive renormalization, in particular, the mass-independent renormalization of massive $\lambda {\varphi }^4$ theory with higher derivative regularization. We then discuss an unconventional scheme to introduce the notion of renormalization point $\mu$ to the subtractive renormalization in a theory defined by a large fixed cutoff $M$. The resulting renormalization group equation generally becomes inhomogeneous, but it is transformed to be homogeneous. The renormalized scalar mass consists of two components in this scheme, one with the ordinary anomalous dimension and the other which is proportional to the renormalization scale $\mu$. This scheme interpolates between the theory defined by dimensional regularization and the theory with unsubtracted quadratic divergences.

An important unanswered question in quantum field theory is to understand precisely under which conditions scale invariance implies invariance under the full conformal group. While the general answer in two dimensions has been known for over 20 years, a precise nonperturbative relation between scale and conformal invariance in higher dimensions has been lacking. In this note, we specialize to four dimensions and give a full quantum mechanical proof that certain unitary $R$-symmetric fixed points are necessarily superconformal. Among other consequences, this result implies that the infrared fixed points of $\mathcal{N}=1$ supersymmetric quantum chromodynamics are superconformal.

We generalize the bumpy black hole framework to allow for alternative theory deformations. We construct two model-independent parametric deviations from the Kerr metric: one built from a generalization of the quasi-Kerr and bumpy metrics and one built directly from perturbations of the Kerr spacetime in Lewis-Papapetrou form. We find the conditions that these “bumps” must satisfy for there to exist an approximate second-order Killing tensor so that the perturbed spacetime still possesses three constants of the motion (a deformed energy, angular momentum and Carter constant) and the geodesic equations can be written in first-order form. We map these parametrized metrics to each other via a diffeomorphism and to known analytical black hole solutions in alternative theories of gravity. The parametrized metrics presented here serve as frameworks for the systematic calculation of extreme mass-ratio inspiral waveforms in parametrized non-general relativity theories and the investigation of the accuracy to which space-borne gravitational wave detectors can constrain such deviations.

We have studied the nonlinear structure formation of the environmentally dependent dilaton model using $N$-body simulations. We find that the mechanism of suppressing the scalar fifth force in high-density regions works very well. Within the parameter space allowed by the solar-system tests, the dilaton model predicts small deviations of the matter power spectrum and the mass function from their $\Lambda \mathrm{CDM}$ counterparts. The importance of taking full account of the nonlinearity of the model is also emphasized.

The heavy spin-$3/2$ baryon-heavy spin-$1/2$ baryon vertices with light vector mesons are studied within the light cone QCD sum rules method. These vertices are parametrized in terms of three coupling constants. These couplings are calculated for all possible transitions. It is shown that correlation functions for these transitions are described by only one invariant function for every Lorenz structure. The obtained relations between the correlation functions of the different transitions are structure independent while explicit expressions of invariant functions depend on the Lorenz structure.

We investigate tensor mesons as quark-antiquark bound states in a fully covariant Bethe-Salpeter equation. As a first concrete step we report results for masses of $J^{PC}=2^{++}$ mesons from the chiral limit up to bottomonium and sketch a comparison to experimental data. All covariant structures of the fermion-antifermion system are taken into account and their roles and importance discussed in two different bases. We also review the general construction principle for covariant Bethe-Salpeter amplitudes of mesons with any spin.

We observe that a recently proposed supersymmetric model with $Q_6$ flavor symmetry admits a new $CP$ violating ground state. A new sum rule for the quark mixing parameters emerges, which is found to be consistent with data. Simple extensions of the model to the neutrino sector suggest an inverted hierarchical mass spectrum with nearly maximal $CP$ violation ($|{\delta }_{\mathrm{MNS}}|\simeq \pi /2$). Besides reducing the number of parameters in the fermion sector, these models also provide solutions to the supersymmetric flavor problem and the supersymmetry $CP$ problem. We construct a renormalizable scalar potential that leads to the spontaneous breaking of $CP$ symmetry and the family symmetry.

We investigate the two-photon corrections to the process $p\overline{p}\to e^{+}{e}^{-}$ at large momentum transfer, aimed to access the timelike nucleon form factors. We estimate the two-photon corrections using a hard rescattering mechanism, which has already been used to calculate the corresponding corrections to elastic electron-proton scattering. Using different nucleon distribution amplitudes, we find that the two-photon corrections to the $p\overline{p}\to e^{+}{e}^{-}$ cross sections in the momentum transfer range $5–30{\mathrm{GeV}}^2$ is below the 1% level.

In the framework of the littlest Higgs model with $T$ parity, we studied the contributions of the new particles to the top-quark pair production via $e^{+}{e}^{-}$ collision at the International Linear Collider. We calculated the top-quark pair production cross section and found this process can generate significantly relative correction. The result may be a sensitive probe of the littlest Higgs model with $T$ parity.

We present a minimal model in which the inverse see saw is realized dynamically. The two unity lepton number-breaking term is induced at two-loop level and is naturally around the keV scale, while right-handed neutrinos are at the TeV scale. An interesting extension of the model is obtained by gauging $B-L$: in this case, anomaly cancellation has as a direct consequence the presence of a sterile neutrino at the MeV scale that may be a good dark matter candidate. Moreover, the new gauge boson $Z^{\prime }$ and the new neutral scalars may have characteristic signatures at LHC.