Sunday, July 22, 2012

Twistors and N=8 Supergravity

Cachazo, Mason and Skinner have given a formula (and its proof) for the complete tree-level S-matrix of N=8 supergravity, using twistor techniques.  As is known, the BCFW recursion relations were initially used to study gluon amplitudes.  Later it was shown that gravity amplitudes also obey such recursion relations.  In N=4 super Yang-Mills BCFW decomposition is related to performing a contour integral in the moduli space of holomorphic maps so as to localize on the boundary where the worldsheet degenerates to a nodal curve.  The summands on the right hand side of the recursion relation correspond to the various ways the vertex operators and map degree may be distributed among the two curve components (see above picture). 

The formula is a big step in moving towards a motivic formulation of gravity.  Moreover, as N=8 supergravity in four dimensions can be recovered from a toroidal compactification of M-theory, it would be interesting to understand the formula in an 'oxidized' context in eleven dimensions.

Wednesday, July 04, 2012

5 Sigma Evidence for Higgs!

The CERN CMS team reports a combined significance of over 5 sigma!  ATLAS also reports 5 sigma evidence.  A new "Higgs-like" boson particle has been discovered.  But is the new 125 GeV particle a Standard Model Higgs? (Note: If Standard Model is valid up to GUT or Planck scale, with top quark mass 174 GeV, 130 GeV is a lower limit on the Higgs mass from the requirement of vacuum stability.  Whereas, with the Minimal Supersymmetric Standard Model (MSSM), for example, the lightest Higgs must necessarily be lighter than 130 GeV.)  Stay tuned...

Tuesday, July 03, 2012

A Higgs Found?

An official CERN video appeared on posts at viXra log and TRF, turning the Higgs rumors into solid evidence for a new particle.  As stated in the video, this new boson has an even numbered spin and behaves very much like a Higgs particle (with 125 GeV mass).  So the question remains: is this a Standard Model Higgs boson?  As noted by John Ellis, the present electroweak vacuum is unstable for a light Higgs in the range 114-135 GeV, requiring new physics to stabilize it (see TRF for a detailed discussion).

By later this year, the identity of the newly found particle should be known.  And if we're lucky, another particle could be found (e.g. a Z' boson), telling us more about which models are best suited for describing our universe.