LIGHT PSEUDOSCALAR BOSONS, PVLAS AND DOUBLE PULSAR J07373039

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LIGHT PSEUDOSCALAR BOSONS, PVLAS AND DOUBLE
PULSAR J0737-3039

• Marco Roncadelli, INFN Pavia (Italy)

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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.

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• 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).

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• 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.

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

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• 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.

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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

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• 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.

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

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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 .

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

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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

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• 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!

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DOUBLE PULSAR J0737-3039

• Discovered in 2003.
• Orbital period T 2.45 h.
• Rotation periods P(A) 23 ms, P(B)
• 2.8 s.
• Inclination of orbital plane i 90.29 deg . it
  is seen almost EDGE-ON.
• Focus on emission from A.

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• 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).

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• 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.

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• 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. 95 211302 (2005)).

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• 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

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• N.B. Effect relevant ABOVE 10 MeV . remarkable
  result!
• For,
• J0737-3039 is expected to be a gamma-ray SOURCE.
• Interaction of photon beam with plasma in
  magnetosphere of B is NEGLIGIBLE.
• WKB approximation JUSTIFIED.

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• 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.

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• 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

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

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• 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.