LIGHT PSEUDOSCALAR BOSONS, PVLAS AND DOUBLE PULSAR J Marco Roncadelli, INFN – Pavia (Italy)

LIGHT PSEUDOSCALAR BOSONS Light pseudoscalar bosons (LPBs) are described by and so are labelled by m and M. LPBs are present in many extensions of the SM.

Most well known example of a LPB is the AXION proposed to solve the strong CP problem. It is characterized by the relation with k = O(1).

As a rule, LPBs are very WEAKLY coupled to matter …. quite ELUSIVE in collider experiments. In the presence of an EXTERNAL magnetic field B, mass eigenstates of photon-LPB system DIFFER from interaction eigenstates …. photon-LPB INTERCONVERSION occurs. N.B. ANALOGY with neutrino oscillations BUT here nonvanishing B necessary to account for spin mismatch.

…. High-precision optics experiments CAN detect LPBs. Two remarks: Transition probability becomes energy- INDEPENDENT for oscillation wavenumber DOMINATED by photon-LPB mixing term.

As long as photon/LPB energy is MUCH LARGER than m – WKB approximation – the SECOND-order propagation equation for a monochromatic beam reduces to a FIRST-order one.

PHOTON PROPAGATION Photon beam propagates along z-axis. Only TRANSVERSE B component is relevant. Suppose B is homogeneous. DEF : PARALLEL photons are polarized in B-z plane, PERPENDICULAR photons have polarization normal to that plane. It turns out that

PARALLEL photons MIX with LPBs. PERPENDICULAR photons do NOT …. they propagate UNDISTURBED. Because of this fact Exchange of a virtual LPB …. BIREFRINGENCE. Production of a real LPB …. DICHROISM.

Consider a photon beam LINEALY polarized at the beginning. Then Owing to BIREFRINGENCE it devolops an ELLIPTICAL polarization. Due to DICHROISM, the ellipse’s major axis is ROTATED. Measuring both ellipticity and rotation angle …. both m and M can be DETERMINED.

ASTROPHYSICAL CONSTRAINT Thermal photons produced in central regions of stars can become LPBs in the fluctuating EM field of stellar plasma. These LPBs escape …. star looses energy …. central temperature increases …. observed properties change. Agreement between standard stellar models and observations …. unwanted LPB effects have to be sufficiently suppressed ….

lower bound N.B. SAME conclusion reached from CAST experiment (no observation of LPBs from the Sun).

PVLAS EXPERIMENT Actually PVLAS collaboration implemented above strategy and reported positive evidence for a LPB with A look back at m-M relation …. this LPB is NOT the axion. Moreover, astrophysical bound

VIOLATED by 5 orders of magnitudes …. …. not only a NEW PARTICLE has been discovered (?) but also NEW PHYSICS al low-energy MUST exist! Sic stantibus rebus…. INDEPENDENT CHECKS of PVLAS claim are COMPELLING!

DOUBLE PULSAR J Discovered in Orbital period T = 2.45 h. Rotation periods P(A) = 23 ms, P(B) = 2.8 s. Inclination of orbital plane i = deg …. it is seen almost EDGE-ON. Focus on emission from A.

Pulsar B has DIPOLAR magnetic field B on the surface. LARGE impact parameter …. NOTHING interesting happens. SMALL impact parameter …. beam from A traverses magnetosphere of B …. photon-LPB conversion IMPORTANT (depending on m, M).

TWO effects are expected. Production of real LPBs …. periodic attenuation of photon beam which depends on T, P(B). N.B. Analog of DICHROISM in PVLAS experiment.

Exchange of virtual LPBs …. periodic LENSING which depends on T, P(B). N.B. Analog of BIREFRINGENCE in PVLAS experiment. Here I consider only attenuation effect (A. Dupays, C. Rizzo, M. R., G. F. Bignami, Phys. Rev.Lett (2005)).

We work within WKB approximation and solve numerically the first-order propagation equation for an UNPOLARIZED, monochromatic beam travelling in the dipolar B produced by pulsar B. Resulting transition probability as a function of beam frequency is

N.B. Effect relevant ABOVE 10 MeV …. remarkable result! For, J is expected to be a gamma- ray SOURCE. Interaction of photon beam with plasma in magnetosphere of B is NEGLIGIBLE. WKB approximation JUSTIFIED.

INTUITIVE explanation assuming B constant i.e. for Mixing effects important for mixing angle in photon-LPB system of order 1 …. OK with THRESHOLD behaviour.

Transition probability becomes energy- independent for oscillation wavenumber dominated by photon-LPB mixing term …. OK with FLAT behaviour. TEMPORAL behaviour best described by TRANSMISSION = 1 – P. We find beam attenuation up to 50 % as

This effect turns out to be OBSERVABLE with GLAST. For example, ABSENCE of attenuation A at 10 % level yields the exclusion plot

This attenuation requires 100 counts during observation time. For 2 weeks in agreement with expectations and about 1000 times LARGER that GLAST sensitivity threshold for point sources.