We calculate the electromagnetic pion form factor in lattice QCD with $2+1$ flavors of the dynamical overlap quarks. Up and down quark masses are set below their physical values so that the system is in the so-called $\epsilon$ regime with the small size of our lattice $\sim 1.8\mathrm{fm}$. The finite volume corrections are generally expected to be $\sim 100\%$ in the $\epsilon$ regime. We, however, find a way to automatically cancel the dominant part of them. Inserting nonzero momenta and taking appropriate ratios of the two- and three-point functions, we can eliminate the contribution from the zero-momentum pion mode. Then the remaining finite volume effect is a small perturbation from the nonzero modes. Our lattice data agree with this theoretical prediction and the extracted pion charge radius is consistent with the experiment.

We introduce new Lorentz-symmetry violating kinematics for a four-fermion interaction model, where dynamical mass generation is allowed, irrespective of the strength of the coupling. In addition, these kinematics lead to a quasirelativistic dispersion relation, in the sense that it is relativistic in both the infrared and the ultraviolet, but not in an intermediate regime, characterized by the mass $M$. For two fermions, we show that a flavor-mixing mass matrix is generated dynamically, and the Lorentz symmetric limit $M\to \infty$ leads to two free relativistic fermions, with flavor oscillations. This model, valid for either Dirac or Majorana fermions, can describe any set of phenomenological values for the eigenmasses and the mixing angle.

Higgs inflation has received remarkable attention in the last few years due to its simplicity and predictive power. The key point of this model is the nonminimal coupling to gravity in unitary gauge. As such, this theory is in fact a scalar-tensor modification of gravity that needs to be studied also below the energy scales of inflation. Motivated by this goal, we study in great analytical and numerical detail the static and spherically symmetric solutions of the equations of motion in the presence of standard baryonic matter, called “Higgs monopoles” and presented in Füzfa et al. [Phys. Rev. Lett. 111, 12 (2013)]. These particlelike solutions may arise naturally in tensor-scalar gravity with Mexican hat potential and are the only globally regular asymptotically flat solutions with finite classical energy. In the case when the parameters of the potential are taken to be the ones of the standard model, we find that the deviations from general relativity are extremely small, especially for bodies of astrophysical size and density. This allows us to derive a simplified description of the monopole, for which the metric inside the spherical matter distribution can be approximated by the standard metric of general relativity. We study how the properties of these monopoles depend on the strength of the nonminimal coupling to gravity and on the baryonic mass and compactness. An important and original result is the existence of a mechanism of resonant amplification of the Higgs field inside the monopole that comes into play for large nonminimal coupling. We show that this mechanism might degenerate into divergences of the Higgs field that reveal the existence of forbidden combinations of radius and baryonic energy density.

Considering a model with coupled dilaton-squared curvature terms and a dilatonic potential that replace the cosmological constant, we present an analytic hyperscaling violating solution which is the generalization of Knodel and Liu [arXiv:1305.3279] for nonzero $\theta$. We show that a specific coupling between the dilaton and the squared curvature terms produces a simple logarithmic behavior for the dilaton. By imposing causality, a null energy condition, and stability constraints, we investigate the allowed regions for the parameters of this model. We then study the perturbations around ${\mathrm{AdS}}_4$ in the UV and around ${\mathrm{AdS}}_2\times {\mathbb{R}}^2$ in the IR of the Einstein-Weyl gravity that can support an intermediate hyperscaling violating solution in order to resolve the IR singularity of the metric in four dimensions.

We study the large scale structure formation in Eddington-inspired Born-Infeld (EiBI) gravity. It is found that the linear growth of scalar perturbations in EiBI gravity deviates from that in general relativity for modes with large wave numbers ($k$), but the deviation is largely suppressed with the expansion of the Universe. We investigate the integrated Sachs-Wolfe effect in EiBI gravity, and find that its effect on the angular power spectrum of the anisotropy of the cosmic microwave background is almost the same as that in the Lambda–cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model. We further calculate the linear matter power spectrum in EiBI gravity and compare it with that in the $\mathrm{\Lambda }\mathrm{CDM}$ model. Deviation is found on small scales ($k\gtrsim 0.1h{\mathrm{Mpc}}^{-1}$), which can be tested in the future by observations from galaxy surveys.

The search for sharp features in the gamma-ray spectrum is a promising approach to identify a signal from dark matter annihilations over the astrophysical backgrounds. In this paper we investigate the generation of gamma-ray lines and internal bremsstrahlung signals in a toy model where the dark matter particle is a real scalar that couples to a lepton and an exotic fermion via a Yukawa coupling. We show that the Fermi-LAT and H.E.S.S. searches for linelike spectral features severely constrain regions of the parameter space where the scalar dark matter is thermally produced. Finally, we also discuss the complementarity of the searches for sharp spectral features with other indirect dark matter searches, as well as with direct and collider searches.

We demonstrate that self-interacting dark matter models with interactions mediated by light particles can have significant deviations in the matter power spectrum and detailed structure of galactic halos when compared to a standard cold dark matter scenario. While these deviations can take the form of suppression of small-scale structure that are in some ways similar to that of warm dark matter, the self-interacting models have a much wider range of possible phenomenology. A long-range force in the dark matter can introduce multiple scales to the initial power spectrum, in the form of dark acoustic oscillations and an exponential cutoff in the power spectrum. Using simulations we show that the impact of these scales can remain observationally relevant up to the present day. Furthermore, the self-interaction can continue to modify the small-scale structure of the dark matter halos, reducing their central densities and creating a dark matter core. The resulting phenomenology is unique to these type of models.

In this paper we address the issue of exploring some cosmological scenarios in modified Einstein gravity through nondynamical (auxiliary) fields. We found that all scenarios are controlled by a specific parameter associated with an auxiliary field. We explore the emergence of inflationary, radiation, matter, and dark energy dominated regimes. Furthermore, an interesting possibility, such as the emergence of a self-tuning mechanism to the cosmological constant problem in the radiation dominated era, is also discussed.

We explore the impact of modified gravity on $B$-modes, identifying two main separate effects: lensing and propagation of tensor modes. The location of the inflationary peak of the $BB$ spectrum depends on the speed of gravitational waves; the amplitude of the lensing contribution depends on the anisotropic stress. We single out these effects using the quasistatic regime and considering models for which the background and the growth of matter perturbations are standard. Using available data we obtain that the gravitational wave speed is compatible with the speed of light and constrained to within about 10%.

Terrestrial gamma-ray flashes (TGFs) are short intense flashes of gamma rays associated with lightning activity in thunderstorms. Using Monte Carlo simulations of the relativistic runaway electron avalanche (RREA) process, theoretical predictions for the temporal and spectral evolution of TGFs are compared to observations made with the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope. Assuming a single source altitude of 15 km, a comparison of simulations to data is performed for a range of empirically chosen source electron variation time scales. The data exhibit a clear softening with increased source distance, in qualitative agreement with theoretical predictions. The simulated spectra follow this trend in the data, but tend to underestimate the observed hardness. Such a discrepancy may imply that the basic RREA model is not sufficient. Alternatively, a TGF beam that is tilted with respect to the zenith could produce an evolution with source distance that is compatible with the data. Based on these results, we propose that the source electron distributions of TGFs observed by GBM vary on time scales of at least tens of microseconds, with an upper limit of $\sim 100\mu \mathrm{s}$.

We investigate the possibility that the cosmic ray (CR) knee is entirely explained by the energy-dependent CR leakage from the Milky Way. We test this hypothesis calculating the trajectories of individual CRs with energies between $E/Z={10}^{14}\mathrm{eV}$ and ${10}^{17}\mathrm{eV}$ propagating them in the regular and turbulent Galactic magnetic field. We find a knee-like structure of the CR escape time ${\tau }_{\text{esc}}(E)$ around $E/Z=\text{few}\times {10}^{15}\mathrm{eV}$ for a coherence length $l_{\mathrm{c}}\simeq 2\mathrm{pc}$ of the turbulent field, while the decrease of ${\tau }_{\text{esc}}(E)$ slows down around $E/Z\simeq {10}^{16}\mathrm{eV}$ in models with a weak turbulent magnetic field. Assuming that the injection spectra of CR nuclei are power laws, the resulting CR intensities in such a turbulence are consistent with the energy spectra of CR nuclei determined by KASCADE and KASCADE-Grande. We calculate the resulting CR dipole anisotropy as well as the source rate in this model.

Flavor symmetries appropriate for describing a neutrino spectrum with degenerate solar pair and a third massive or massless neutrino are discussed. We demand that the required residual symmetries of the leptonic mass matrices be subgroups of some discrete symmetry group $G_f$. $G_f$ can be a subgroup of $SU(3)$ if the third neutrino is massive and we derive general results on the mixing angle predictions for various discrete subgroups of $SU(3)$ divided into the two classes, called type C and D in Miller et al. [Theory and Applications of Finite Groups (John Wiley & Sons, New York, 1916)]. The main results are (a) All the $SU(3)$ subgroups of type C fail in simultaneously giving correct ${\theta }_{13}$ and ${\theta }_{23}$. (b) All the groups of type D can predict a relation ${\cos }^2{\theta }_{13}{\sin }^2{\theta }_{23}=\frac{1}{3}$ among the mixing angles which appears to be a good zeroth order approximation. Among these, various $\mathrm{\Delta }(6n^2)$ groups with $n\ge 8$ can simultaneously lead also to ${\sin }^2{\theta }_{13}$ in agreement with global fit at $3\sigma$. (c) The group $\mathrm{\Sigma }(168)\cong PSL(2,7)$ predicts near to the best fit value for ${\theta }_{13}$ and ${\theta }_{23}$ within the $1\sigma$ range. All discrete subgroups of $U(3)$ with order $<512$ and having three-dimensional irreducible representation are considered as possible $G_f$ when the third neutrino is massless. Only seven of them are shown to be viable and three of these can correctly predict ${\theta }_{13}$ and/or ${\theta }_{23}$. The solar angle remains undetermined at the leading order in all the cases due to degeneracy in the masses. A class of general perturbations which can correctly reproduce all the observables is discussed in the context of several groups which offer good leading order predictions.

Both the naturalness of the electroweak symmetry breaking and the resolution of the strong CP problem may require a small Higgsino mass $\mu$ generated by a realization of the DFSZ axion model. Assuming the axino is the lightest supersymmetric particle, we study its implications on $\mu$ and the axion scale. Copiously produced light Higgsinos at collider (effectively only neutral next-to-lightest superparticles pairs) eventually decay to axinos leaving prompt multileptons or displaced vertices which are being looked for at the LHC. We use latest $\mathrm{LHC}7+8$ results to derive current limits on $\mu$ and the axion scale. Various Higgsino-axino phenomenology is illustrated by comparing with a standard case without lightest axinos as well as with a more general case with additional light gauginos in the spectrum.

We study the impact of the existence of an eV-mass scale sterile neutrino—with parameters in the ballpark of what is required to fit the laboratory anomalies—on the early time profile of the electron neutrino and antineutrino fluxes associated to a core-collapse supernova (SN). In particular, we focus on the universal feature of neutronization burst expected in the first tens of ms of the signal: Provided that a detector with sufficient sensitivity is available, it is well known that in the three-neutrino framework the detection of the neutronization burst in neutrino channel would signal inverted mass hierarchy. This conclusion is dramatically altered in the presence of a sterile neutrino: We study here, both analytically and numerically, the region in parameter space where this characteristic signal disappears, mimicking normal hierarchy expectations. Conversely, the detection of a peak consistent with expectations for inverted mass hierarchy would exclude the existence of a sterile state over a much wider parameter space than what is required by laboratory anomaly fits, or is even probed by detectors coming on-line in the near future. Additionally, we show the peculiar alteration in the energy-time double differential flux, with a delayed peak appearing for kinematical reasons, which might offer a remarkable signature in the case of favorable parameters and for a high statistics detection of a Galactic SN. We also comment on additional potentially interesting effects in the electron antineutrino channel, if more than one angle in the active-sterile sector is nonvanishing. As an ancillary result that we derived in the technical resolution of the equations, in an Appendix we report the Cayley-Hamilton formalism for the evolution of a four-neutrino system in matter, generalizing existing results in the literature.

A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of $19.5{\mathrm{fb}}^{-1}$ of proton-proton collisions with center-of-mass energy $\sqrt{s}=8\mathrm{TeV}$, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying $\tau$ leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson ($t\to cH$), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, ${\lambda }_{tc}^H$ and ${\lambda }_{ct}^H$, respectively, of $\sqrt{|{\lambda }_{tc}^H{|}^2+|{\lambda }_{ct}^H{|}^2}<0.21$.

We derive a simple expression for the photon helicity and polarization-flip probabilities in arbitrary background fields, in the low-energy regime. Taking the background to model a focused laser beam, we study the impact of pulse shape and collision geometry on the probabilities and on ellipticity signals of vacuum birefringence. We find that models which do not account for pulse duration can overestimate all signals in near head-on collisions by up to an order of magnitude. Taking pulse duration into account, the flip probability becomes relatively insensitive to both angular incidence and the fine details of the pulse structure.

The decay of the vacuum due to the presence of an electric field is expected to be delayed by a confining force. We demonstrate that this feature is captured by our model for hadrons based on the worldline formalism. Our model, while based entirely in four-dimensional quantum field theory, shares many features with holographic approaches: it appears intrinsically quantum mechanical; as an auxiliary fifth dimension Schwinger’s proper time combines with the physical four spacetime dimensions into an ${\mathrm{AdS}}_5$ geometry; conformal-symmetry breaking contributions lead to warping; hidden local symmetry emerges; four-dimensional sources are extended to five-dimensional fields by a Wilson flow (gradient flow); and a variational principle for this flow reproduces the corresponding holographic calculation. The approach also yields the higher-dimensional description in the nonrelativistic case.

Ozawa’s measurement-disturbance relation is generalized to a phase-space noncommutative extension of quantum mechanics. It is shown that the measurement-disturbance relations have additional terms for backaction evading quadrature amplifiers and for noiseless quadrature transducers. Several distinctive features appear as a consequence of the noncommutative extension: measurement interactions which are noiseless, and observables which are undisturbed by a measurement, or of independent intervention in ordinary quantum mechanics, may acquire noise, become disturbed by the measurement, or no longer be an independent intervention in noncommutative quantum mechanics. It is also found that there can be states which violate Ozawa’s universal noise-disturbance trade-off relation, but verify its noncommutative deformation.

We investigate the possibility of explaining theoretically the observed deviations of S2 star orbit around the Galactic Centre using gravitational potentials derived from modified gravity models in the absence of dark matter. To this aim, an analytic fourth-order theory of gravity, nonminimally coupled with a massive scalar field, is considered. Specifically, the interaction term is given by the analytic functions $f(R)$ and $f(R,\varphi )$ where $R$ is the Ricci scalar and $\varphi$ is a scalar field whose meaning can be related to further gravitational degrees of freedom. We simulate the orbit of the S2 star around the Galactic Centre in $f(R)$ (Yukawa-like) and $f(R,\varphi )$ (Sanders-like) gravity potentials and compare it with New Technology Telescope/Very Large Telescope observations. Our simulations result in strong constraints on the range of gravity interaction. In the case of analytic functions $f(R)$, we are not able to obtain reliable constraints on the derivative constants $f_1$ and $f_2$, because the current observations of the S2 star indicated that they may be highly mutually correlated. In the case of analytic functions $f(R,\varphi )$, we are able to obtain reliable constraints on the derivative constants $f_0$, $f_R$, $f_{RR}$, $f_{\varphi }$, $f_{\varphi \varphi }$, and $f_{\varphi R}$. The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around the Galactic Centre.