This paper describes the 25 year effort to measure vacuum magnetic birefringence and dichroism with the PVLAS experiment. The experiment went through two main phases: the first using a rotating ...superconducting magnet and the second using two rotating permanent magnets. The experiment was not able to reach the predicted value from QED. Nonetheless the experiment has set the current best limits on vacuum magnetic birefringence and dichroism for a field of Bext=2.5 T, namely, Δn(PVLAS)=(12±17)×10−23 and |Δκ|(PVLAS)=(10±28)×10−23. The uncertainty on Δn(PVLAS) is about a factor 7 above the predicted value of Δn(QED)=2.5×10−23 @ 2.5 T.
The PVLAS collaboration is presently assembling a new apparatus (at the INFN section of Ferrara, Italy) to detect vacuum magnetic birefringence (VMB). VMB is related to the structure of the quantum ...electrodynamics (QED) vacuum and is predicted by the Euler-Heisenberg-Weisskopf effective Lagrangian. It can be detected by measuring the ellipticity acquired by a linearly polarized light beam propagating through a strong magnetic field. Using the very same optical technique it is also possible to search for hypothetical low-mass particles interacting with two photons, such as axion-like (ALP) or millicharged particles. Here we report the results of a scaled-down test setup and describe the new PVLAS apparatus. This latter is in construction and is based on a high-sensitivity ellipsometer with a high-finesse Fabry-Perot cavity (>4 × 105) and two 0.8 m long 2.5 T rotating permanent dipole magnets. Measurements with the test setup have improved, by a factor 2, the previous upper bound on the parameter Ae, which determines the strength of the nonlinear terms in the QED Lagrangian: A(PVLAS)e < 3.3 × 10−21 T−2 at 95% c.l. Furthermore, new laboratory limits have been put on the inverse coupling constant of ALPs to two photons and confirmation of previous limits on the fractional charge of millicharged particles is given.
Although experimental efforts have been active for about 30 years, a direct laboratory observation of vacuum magnetic birefringence, due to vacuum fluctuations, still needs confirmation: the ...predicted birefringence of vacuum is
Δ
n
=
4.0
×
10
-
24
@ 1 T. Key ingredients of a polarimeter for detecting such a small birefringence are a long optical path within the magnetic field and a time dependent effect. To lengthen the optical path a Fabry–Perot is generally used with a finesse ranging from
F
≈
10
4
to
F
≈
7
×
10
5
. Interestingly, there is a difficulty in reaching the predicted shot noise limit of such polarimeters. We have measured the ellipticity and rotation noises along with Cotton-Mouton and Faraday effects as a function of the finesse of the cavity of the PVLAS polarimeter. The observations are consistent with the idea that the cavity mirrors generate a birefringence-dominated noise whose ellipticity is amplified by the cavity itself. The optical path difference sensitivity at
10
Hz
is
S
Δ
D
=
6
×
10
-
19
m
/
Hz
, a value which we believe is consistent with an intrinsic thermal noise in the mirror coatings. Our findings prove that the continuous efforts to increase the finesse of the cavity to improve the sensitivity has reached a limit.
Optical Fabry–Perot cavities always show a non-degeneracy of two orthogonal polarisation states. This is due to the unavoidable birefringence of dielectric mirrors whose effects are extremely ...important in Fabry–Perot-based high-accuracy polarimeters: in birefringent cavities, ellipticities and rotations mix. We have developed and present here a theory of the polarisation state dynamics in a birefringent Fabry–Perot resonator, and we validate it through measurements performed with the polarimeter of the PVLAS experiment. The measurements are performed while a laser is frequency-locked to the cavity, and provide values for the phase difference between the two orthogonal polarisation components introduced by the combination of the two cavity mirrors (equivalent wave-plate) and for the finesse of the cavity. The theoretical formulas and the experimental data agree well showing that the consequences of the mirror birefringence must be taken into account in this and in any other similar experiment.
A novel polarisation modulation scheme for polarimeters based on Fabry–Perot cavities is presented. The application to the measurement of the magnetic birefringence of vacuum with the HERA ...superconducting magnets in the ALPS-II configuration is discussed.
This study analysed the attachment patterns of 28 late-adopted children (placed when they were between four and seven years of age) and their adoptive mothers. The change in the children's internal ...working models (IWMs) within seven to eight months of their placement was evaluated. In addition, we wanted to observe the influence of a secure-autonomous maternal state of mind in facilitating the change in the children's IWMs and the possible associations between the maternal IWMs and the children's IWMs in the adoptive dyads. The separation-reunion procedure (SRP) was used for the late-adopted children in order to assess their attachment behavioural patterns, and the Manchester Child Attachment Story Task (MCAST) was used to evaluate their attachment narrative patterns. The adoptive mothers completed the Adult Attachment Interview (AAI) in order to classify their state of mind with regard to attachment. The results showed a significant change in the attachment behavioural patterns of late-adopted children, from insecure to secure (p = .002). Furthermore, the children who presented this change were predominantly placed with secure-autonomous adoptive mothers (p = .047), although the link between the adoptive mothers' representations of their attachment history and their adopted children's completed narratives was not significant. In conclusion, it seems possible to revise the attachment behaviour of late-adopted children but, for about one-third of children, the adverse history will persist at a narrative/representational level.
This study explores the role of adult attachment configurations on marital satisfaction and conflict strategies during the transition to parenthood in a sample of 206 participants, 104 new parents ...and 102 childless by choice. All participants were administered measures of dyadic satisfaction and conflict strategies at two stages (during pregnancy and after 8 months, when the child was 6 months old). In prospective parents, the participants’ adult attachment configurations were also investigated in line with Crowell’s model. Results showed a decline in satisfaction and a lower use of cooperative conflict strategies for new parents. Secure specific attachment configurations appeared predictable of better satisfaction during the transition to parenthood. Insecure specific attachment configurations were predictable of a lower use of the cooperative strategy of integrating. Results were also explored in terms of the couple’s matching of attachment configurations. Overall, findings showed that in order to study a couple’s functioning it is important to consider the weight of each partner’s attachment configuration.
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