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Post Info TOPIC: Photon-Axion-Like Particle Coupling Constant


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Axion-Like Particles
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Title: Photon-axion conversion in Active Galactic Nuclei?
Authors: Nicola Bassan, Marco Roncadelli

Axion-Like Particles (ALPs) are the focus of intense current research. We analyze photon-ALP conversion in the context of relativistic jet models of Active Galactic Nuclei (AGN) for more than 100 sources. Contrary to previous claims, we find that this process cannot occur above 100 GeV regardless of the actual AGN model and the values of ALP parameters. This result rules out a proposed strategy to bypass the cosmic opacity above 100 GeV, as apparently required by observations. We also show that for some AGN an observable effect can show up in the X and soft gamma-ray bands.

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Photon/axion mixing
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Title: Hints of the existence of Axion-Like-Particles from the gamma-ray spectra of cosmological sources
Authors: M. A. Sanchez-Conde (1,3), D. Paneque (2), E. Bloom (2), F. Prada (1,5), A. Dominguez (1,4) ((1) IAA-CSIC, (2) KIPAC/SLAC National Accelerator Center, (3) Visiting student at KIPAC/SLAC National Accelerator Centre, (4) Universidad de Sevilla, (5) Visiting research physicist at SCIPP, UC Santa Cruz)

Axion Like Particles (ALPs) are predicted to couple with photons in the presence of magnetic fields. This effect may lead to a significant change in the observed spectra of gamma-ray sources such as AGNs. Here we carry out a detailed study that for the first time simultaneously considers in the same framework both the photon/axion mixing that takes place in the gamma-ray source and that one expected to occur in the intergalactic magnetic fields. An efficient photon/axion mixing in the source always means an attenuation in the photon flux, whereas the mixing in the intergalactic medium may result in a decrement and/or enhancement of the photon flux, depending on the distance of the source and the energy considered. Interestingly, we find that decreasing the value of the intergalactic magnetic field strength, which decreases the probability for photon/axion mixing, could result in an increase of the expected photon flux at Earth if the source is far enough. We also find a 30% attenuation in the intensity spectrum of distant sources, which occurs at an energy that only depends on the properties of the ALPs and the intensity of the intergalactic magnetic field, and thus independent of the AGN source being observed. Moreover, we show that this mechanism can easily explain recent puzzles in the spectra of distant gamma-ray sources.

The consequences that come from this work are testable with the current generation of gamma-ray instruments, namely Fermi (formerly known as GLAST) and imaging atmospheric Cherenkov telescopes like CANGAROO, HESS, MAGIC and VERITAS.

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RE: Photon-Axion-Like Particle Coupling Constant
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Title: Search for axion-like particles using a variable baseline photon regeneration technique
Authors: A.S. Chou, W. Wester, A. Baumbaugh, H.R. Gustafson, Y. Irizarry-Valle, P.O. Mazur, J.H. Steffen, R. Tomlin, X. Yang, J. Yoo
(Version v2)

We report the first results of the GammeV experiment, a search for milli-eV mass particles with axion-like couplings to two photons. The search is performed using a "light shining through a wall" technique where incident photons oscillate into new weakly interacting particles that are able to pass through the wall and subsequently regenerate back into detectable photons. The oscillation baseline of the apparatus is variable, thus allowing probes of different values of particle mass. We find no excess of events above background and are able to constrain the two-photon couplings of possible new scalar (pseudoscalar) particles to be less than 3.1x10^{-7} GeV^{-1} (3.5x10^{-7} GeV^{-1}) in the limit of massless particles.

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 Evidence mounts for axion-like particles
Are 'luminosity relations' a key piece in an intergalactic puzzle?

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Posts: 131433
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New Light Boson
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Title: Evidence for a New Light Boson from Cosmological Gamma-Ray Propagation?
Authors: Marco Roncadelli, Alessandro De Angelis, Oriana Mansutti

An anomalously large transparency of the Universe to gamma rays has recently been discovered by the Imaging Atmospheric Cherenkov Telescopes (IACTs) H.E.S.S. and MAGIC. We show that observations can be reconciled with standard blazar emission models provided photon oscillations into a very light Axion-Like Particle occur in extragalactic magnetic fields. A quantitative estimate of this effect is successfully applied to the blazar 3C279. Our prediction can be tested with the satellite-borne Fermi/LAT detector as well as with the ground-based IACTs H.E.S.S., MAGIC, CANGAROOIII, VERITAS and the Extensive Air Shower arrays ARGO-YBJ and MILAGRO. Our result also offers an important observational test for models of dark energy wherein quintessence is coupled to the photon through an effective dimension-five operator.

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Posts: 131433
Date:
Photon-Axion-Like Particle Coupling Constant
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Title: Photon-Axion-Like Particle Coupling Constant and Cosmological Observations
Authors: M. Yu. Piotrovich, Yu. N. Gnedin, T. M. Natsvlishvili

We estimated the photon-pseudoscalar particle mixing constant from the effect of cosmological alignment and cosmological rotation of polarisation plane of distant QSOs. This effect is explained in terms of birefringent phenomenon due to photon-pseudoscalar (axion-like) particle mixing in a cosmic magnetic field. On the contrary, one can estimate the strength of the cosmic magnetic field using the constraints on the photon-axion-like particle coupling constant from the CAST experiment and from SNe Ia dimming effect. In a result, the lower limit on the intergalactic (z ~ 1\div 2) magnetic field appears at the level of about 4 x 10^{-10}\div 10^{-11} G.

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