Photon-axion Oscillations Research Articles

On the origin and the detection of characteristic axion wiggles in photon spectra

Photons propagating in an external magnetic field may oscillate into axions or axion-like particles (ALPs). Such oscillations will lead to characteristic features in the energy spectrum of high-energy photons from astrophysical sources that can be used to probe the existence of ALPs. In this work, we revisit the signatures of these oscillations and stress the importance of a proper treatment of turbulent magnetic fields. We implement axions into ELMAG, a standard tool for modelling in a Monte Carlo framework the propagation of gamma-rays in the Universe, complementing thereby the usual description of photon-axion oscillations with a Monte Carlo treatment of high-energy photon propagation and interactions. We also propose an alternative method of detecting axions through the discrete power spectrum using as observable the energy dependence of wiggles in the photon spectra.

Planck data and ultralight axions

We examine the effects of photon-axion mixing on the CMB. We show that if there are very underdense regions between us and the last scattering surface which contain coherent magnetic fields (whose strength can be orders of magnitude weaker than the current bounds), then photon-axion mixing can induce observable deviations in the CMB spectrum. Specifically, we show that the mixing can give rise to non-thermal spots on the CMB sky. As an example we consider the well known CMB cold spot, which according to the Planck data has a weak distortion from a black body spectrum, that can be fit by our model. While this explanation of the non-thermality in the region of the cold spot is quite intriguing, photon-axion oscillations do not explain the temperature of the cold spot itself. Nevertheless we demonstrate the possible sensitivity of the CMB to ultralight axions which could be exploited by observers.

Constraining the photon-axion coupling constant with magnetic white dwarfs

The light pseudoscalar particle, dubbed the axion, borne out of the Peccei-Quinn solution to the strong CP problem in QCD remains elusive. One avenue of inferring its existence is through its coupling to electromagnetic radiation. So far, laboratory experiments have dedicated all efforts to detect the axion in the mass range $10^{-6} < m_a < 10^{-3}$ eV with a photon-axion coupling strength $g_{a\gamma\gamma} < 10^{-10}GeV^{-1}$, where the limits are derived from astrophysical considerations. In this study, we present a novel way of constraining $g_{a\gamma\gamma}$ by looking at the level of linear polarization in the radiation emerging from magnetic white dwarfs (mWDs). We find that photon-axion oscillations in WD magnetospheres can enhance the degree of linear polarization. Observing that most mWDs show only 5% linear polarization, we derive upper limits on $g_{a\gamma\gamma}$ for different axion masses.

Search for photon oscillations into massive particles

Recently, axionlike particle search has received renewed interest, and several groups have started experiments. In this paper, we present the final results of our experiment on photon-axion oscillations in the presence of a magnetic field, which took place at the Laboratoire pour l'Utilisation des Lasers Intenses, Palaiseau, France. Our null measurement allowed us to exclude the existence of axions with inverse coupling constant $Mg9.\ifmmode\times\else\texttimes\fi{}{10}^{5}\text{ }\text{ }\mathrm{GeV}$ for low axion masses and to improve the preceding Brookhaven-Fermilab-Rochester-Trieste (BFRT) Collaboration limits by a factor of 3 or more for axion masses $1.1l{m}_{a}l2.6\text{ }\text{ }\mathrm{meV}$. We also show that our experimental results improve the existing limits on the parameters of a low mass hidden-sector boson usually dubbed ``paraphoton'' because of its similarity with the usual photon. We detail our apparatus which is based on the ``light shining through the wall'' technique. We compare our results to other existing ones.

Photon-axion conversion as a mechanism for supernova dimming: Limits from CMB spectral distortion

Axion-photon conversion induced by intergalactic magnetic fields has been proposed as an explanation for the dimming of distant supernovae of type Ia (SNe Ia) without cosmic acceleration. The effect depends on the intergalactic electron density ${n}_{e}$ as well as the $B$-field strength and domain size. We show that for ${n}_{e}\ensuremath{\lesssim}{10}^{\ensuremath{-}9}{\text{ }\text{ }\mathrm{cm}}^{\ensuremath{-}3}$ the same mechanism would cause excessive spectral distortion of the cosmic microwave background (CMB). This small-${n}_{e}$ parameter region had been left open by the most restrictive previous constraints based on the dispersion of quasar (QSO) spectra. The combination of CMB and QSO limits suggests that the photon-axion conversion mechanism can only play a subleading role for SN Ia dimming. A combined analysis of all the observables affected by the photon-axion oscillations would be required to give a final verdict on the viability of this model.

Limiting the dimming of distant type Ia supernovae

Distant supernovae have been observed to be fainter than what is expected in a matterdominated universe. The most likely explanation is that the universe is dominated by anenergy component with negative pressure, namely dark energy. However, there are severalastrophysical processes that could, in principle, affect the measurements andin order to be able to take advantage of the growing supernova statistics, thecontrol of systematic effects is crucial. We discuss two of these; extinction due tointergalactic grey dust and dimming due to photon–axion oscillations and show howtheir effect on supernova observations can be constrained using observed quasarcolours and spectra. For a wide range of intergalactic dust models, we are ableto rule out any dimming larger than 0.2 magnitudes for a type Ia supernova atz = 1. The corresponding limit for intergalactic Milky Way type dust is 0.03 magnitudes. For themore speculative model of photons mixing with axions, we find that the effect isindependent of photon energy for certain combinations of parameter values and a dimmingas large as 0.6 magnitudes cannot be ruled out. These effects can have profoundimplications for the possibility of constraining dark energy properties using supernovaobservations.

Constraining photon–axion oscillations using quasar spectra

Using quasar spectra from the SDSS survey, we constrain thepossibility of photon–axion oscillations as a source of dimming ofhigh redshift objects. Such a process has been suggested as anexplanation of the apparent faintness of distant Type Iasupernovae. For most combinations of magnetic field strengths andplasma densities along the line of sight, large beam attenuations inbroad-band filters would also lead to significant differentialattenuation, not observed in the quasar sample. However, thisconservative study does not exclude the possibility of ∼0.1 magdimming of Type Ia supernovae for average plasma densities ne ≲ 10−8 cm−3. NIR and MIR spectroscopic studies of high-zsources may be used to put further constraints or provide indirectevidence for the existence of a very light axion.

SNOC: A Monte-Carlo simulation package for high-zsupernova observations

We present a Monte-Carlo package for simulation of high-redshift supernova data, SNOC. Optical and near-infrared photons from supernovae are ray-traced over cosmological distances from the simulated host galaxy to the observer at Earth. The distances to the sources are calculated from user provided cosmological parameters in a Friedmann-Lemaˆ itre universe, allowing for arbitrary forms of dark energy. The code takes into account gravitational interactions (lensing) and extinction by dust, both in the host galaxy and in the line-of-sight. The user can also choose to include exotic eects like a hypothetical attenuation due to photon-axion oscillations. SNOC is primarily useful for estimations of cosmological parameter uncertainties from studies of apparent brightness of type Ia supernovae vs redshift, with special emphasis on potential systematic eects. It can also be used to compute standard cosmological quantities like luminosity distance, lookback time and age of the universe in any Friedmann-Lemaˆ itre model with or without quintessence.

Photon-axion oscillations and type Ia supernovae

We compute the probability of photon-axion oscillations in the presence of both intergalactic magnetic fields and an electron plasma and investigate the effect on type Ia supernovae observations. The conversion probability is calculated using a density matrix formalism by following light paths through simulated universes in a Monte Carlo fashion. We find that, even though the effect is highly frequency dependent, one needs to analyze relatively narrow spectral features of high redshift objects in order to discriminate between the dimming effect from oscillations and a cosmological constant, in contrast with earlier claims that broadband photometry is sufficient. However, it should be possible to put severe constraints on the effect by studying, e.g., quasar-, gamma-ray burst-, and galaxy-spectra.

Effects of the intergalactic plasma on supernova dimming via photon–axion oscillations

We have recently proposed a mechanism of photon–axion oscillations as a way of rendering supernovae dimmer without cosmic acceleration. Subsequently, it has been argued that the intergalactic plasma may interfere adversely with this mechanism by rendering the oscillations energy dependent. Here we show that this energy dependence is extremely sensitive to the precise value of the free electron density in the Universe. Decreasing the electron density by only a factor of 4 is already sufficient to bring the energy dependence within the experimental bounds. Models of the intergalactic medium show that for redshifts z<1 about 97% of the total volume of space is filled with regions of density significantly lower than the average density. From these models we estimate that the average electron density in most of space is lower by at least a factor of 15 compared to the estimate based on one half of all baryons being uniformly distributed and ionized. Therefore the energy dependence of the photon–axion oscillations is consistent with experiment, and the oscillation model remains a viable alternative to the accelerating Universe for explaining the supernova observations. Furthermore, the electron density does give rise to a sufficiently large plasma frequency which cuts off the photon–axion mixing above microwave frequencies, shielding the cosmic microwave photons from axion conversions and significantly relaxing the lower bounds on the axion mass implied by the oscillation model.