Related papers: Scalar Cherenkov radiation from high-energy cosmic…
Dark energy is often assumed to be composed by a single scalar field. The background cosmic expansion is not sufficient to determine whether this is true or not. We study multi-field scalar-tensor models with a general dark matter source…
We study the cosmological evolution of a scalar field that couples to the trace $T=T^{a}_a$ of energy momentum tensor of all the fields (including itself). In the case of a shallow exponential potential, the presence of coupling to the…
An attractive method of obtaining an effective cosmological constant at the present epoch is through the potential energy of a scalar field. Considering models with a perfect fluid and a scalar field, we classify all potentials for which…
The simplest way to modify gravity is to extend the gravitational sector to include an additional scalar degree of freedom. The most general metric that can be built in such a theory includes disformal terms, so that standard model fields…
The cross-section for the lowest order $2\rightarrow2$ elastic scattering between two charged scalars under external magnetic field mediated via a neutral scalar, has been computed in strong as well as weak magnetic field limits. This has…
Ultra-High-Energy Cosmic Rays (UHECRs), particles characterized by energies exceeding $10^{18}$ eV, are generally believed to be accelerated electromagnetically in high-energy astrophysical sources. One promising mechanism of UHECR…
The existence of scalar fields can be probed by observations of stochastic gravitational waves. Scalar fields mediate attractive forces, usually stronger than gravity, on the length scales shorter than their Compton wavelengths, which can…
We treat a very crude model of an exploding star, in the weak field approximation of the Brans-Dicke theory, in a scenario that resembles some characteristics data of a Type Ia Supernova. The most noticeable feature, in the electromagnetic…
We investigate the radiation from an inertial scalar particle evolving in a de Sitter expanding Universe. In the context of scalar QED the process is generated by the first order term in the perturbation theory expansion of the S-matrix.…
Many candidate fundamental theories contain scalar fields that can acquire spacetime-varying expectation values in a cosmological context. Such scalars typically obey Lorentz-violating effective dispersion relations. We illustrate this fact…
It is commonly accepted that high energy cosmic rays up to $10^{19}$ eV can be produced in catastrophic astrophysical processes. However the source of a few observed events with higher energies remains mysterious. We propose that they may…
I review the effective field theory (EFT) description of gravitating compact objects. The focus is on kinematic regimes where gravity is perturbative, in particular the adiabatic inspiral phase relevant to gravitational wave detection. For…
A model is introduced, in which the irregularity spectrum of the Galactic magnetic field beyond the dissipation length scale is first a Kolmogorov spectrum $k^{-5/3}$ at small scales $\lambda \, = \, 2 \pi/k$ with $k$ the wave-number, then…
Specific action for isotropic fluctuations of scalar field is derived under the condition of 4D cut-off. It is implemented into the estimates of dark energy scale consistent with current cosmological data.
The energy-dependent abundance of elements in cosmic rays plays an important role in understanding their acceleration and propagation. Most current results are obtained either from direct measurements by balloon- or satellite-borne…
We investigate the propagation of a charged particle in a spatially constant but time dependent pseudoscalar background. Physically this pseudoscalar background could be provided by a relic axion density. The background leads to an explicit…
Recent observations on ultra high energy cosmic rays (those cosmic rays with energies greater than $\sim 4 \times 10^{18}$ eV) suggest an abundant flux of incoming particles with energies above $1 \times 10^{20}$ eV. These observations…
We present the results of a study that simulates trajectories of ultra-high energy cosmic rays from Centaurus A to Earth, for particle rigidities from $E/Z = 2$ EV to 100 EV, i.e., covering the possibility of primary particles as heavy as…
Cosmic ray electrons represent a background for gamma-ray observations with Cherenkov telescopes, initiating air-showers which are difficult to distinguish from photon-initiated showers. This similarity, however, and the presence of cosmic…
We perform the first study of the oscillation frequencies of rapidly rotating neutron stars in alternative theories of gravity, focusing mainly on the fundamental $f$-modes. We concentrated on a particular class of alternative theories -…