I have read through the thread and let me add something.
In accord with special relativity, a massless particle has only two
spin states. For a spin one gauge boson (e.g. photon or gluon), these
two states (z component +-1 are related to the polarization and
correspond to two perpendicular transverse polarizations. A massive
spin one gauge boson (e.g. the Z and W bosons of the weak
interaction) has three spin states. The spin zero state corresponds
to longitudinal polarization. A real gauge boson has zero mass and
two spin states. A virtual gauge boson has mass and thus three spin
states. Thus a virtual photon exhibits longitudinal polarization.
(The graviton is more complicated. It has spin two. Nonetheless, a
real graviton is massless and has according to special relativity
only two spin states.)
--
Best wishes
Calvin
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
_/ Calvin S. Kalman, P. Phys. Phone: (514) 848-2424 xt 3284
_/ Professor,Department of Physics Fax: (514) 848-2828
_/ Fellow, Science College
_/ Concordia University
_/ Montreal, QC H4B 1R6 Calvin.Kalman@concordia.ca
_/
_/ Also Adjunct Professor Department of Educational
_/ and Counseling Psychology, McGill University, Montreal, Quebec
_/
_/
_/ homepage- http://physics.concordia.ca/faculty/ckalman.php
_/
_/ Buy
_/ Successful Science and Engineering Teaching in Colleges and Universities
_/ at
_/ http://www.josseybass.com/WileyCDA/WileyTitle/productCd-1933371161.html
_/ See review found in the Journal of Chemical Education Oct. 2007:
_/ http://tinyurl.com/2rt7tj
_/
_/ For the research behind this book buy:
_/ "Successful Science and Engineering Teaching: Theoretical and Learning
_/ Perspectives (Innovation and Change in Professional Education)"
_/ at
_/ http://tinyurl.com/3qn237
_/
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