41 research outputs found
Dipole Modulation in Tensor Modes: Signatures in CMB Polarization
In this work we consider a dipole asymmetry in tensor modes and study the
effects of this asymmetry on the angular power spectra of CMB. We derive
analytical expressions for the and in the presence of
such dipole modulation in tensor modes for . We also discuss on the
amplitude of modulation term and show that the is considerably
modified due to this term.Comment: 12 pages, 5 figure
Photon-graviton scattering: A new way to detect anisotropic gravitational waves?
Gravitons are the quantum counterparts of gravitational waves in low-energy
theories of gravity. Using Feynman rules one can compute scattering amplitudes
describing the interaction between gravitons and other fields. Here, we
consider the interaction between gravitons and photons. Using the quantum
Boltzmann equation formalism, we derive fully general equations describing the
radiation transfer of photon polarization, due to the forward scattering with
gravitons. We show that the Q and U photon linear polarization modes couple
with the V photon circular polarization mode, if gravitons have anisotropies in
their power-spectrum statistics. As an example, we apply our results to the
case of primordial gravitons, considering models of inflation where an
anisotropic primordial graviton distribution is produced. Finally, we evaluate
the effect on cosmic microwave background (CMB) polarization, showing that in
general the expected effects on the observable CMB frequencies are very small.
However, our result is promising, since it could provide a novel tool for
detecting anisotropic backgrounds of gravitational waves, as well as for
getting further insight on the physics of gravitational waves.Comment: 15 pages, 1 figure. v2: references added, typos corrected, replaced
to match published version in PR
Induced Circular Polarization on Photons Due to Interaction with Axion-Like Particles in Rotating Magnetic Field of Neutron Stars
We investigate how the photon polarization is affected by the interaction
with axion-like particles (ALPs) in the rotating magnetic field of a neutron
star (NS). Using quantum Boltzmann equations the study demonstrates that the
periodic magnetic field of millisecond NSs enhances the interaction of photons
with ALPs and creates a circular polarization on them. A binary system
including an NS and a companion star could serve as a probe. When the NS is in
front of the companion star with respect to the earth observer, there is a
circular polarization on the previously linearly polarized photons as a result
of the interaction with ALPs there. After a half-binary period, the companion
star passes in front of the NS, and the circular polarization of photons
disappears and changes to linear. The excluded parameter space for a
millisecond NS with 300~Hz rotating frequency, highlights the coupling constant
of for the ALP masses in
the range of .Comment: 31 pages, 5 figure