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Post Info TOPIC: Special unitary group SU(2)
Blobrana


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ElectroWeak Symmetry Breaking
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Title: Are There Hints of Light Stops in Recent Higgs Search Results?
Authors: Matthew R. Buckley, Dan Hooper

The recent discovery at the LHC by the CMS and ATLAS collaborations of the Higgs boson presents, at long last, direct probes of the mechanism for electroweak symmetry breaking. While it is clear from the observations that the new particle plays some role in this process, it is not yet apparent whether the couplings and widths of the observed particle match those predicted by the Standard Model. In this paper, we perform a global fit of the Higgs results from the LHC and Tevatron. While these results could be subject to as-yet-unknown systematics, we find that the data are significantly better fit by a Higgs with a suppressed width to gluon-gluon and an enhanced width to gamma gamma, relative to the predictions of the Standard Model. After considering a variety of new physics scenarios which could potentially modify these widths, we find that the most promising possibility is the addition of a new colored, charged particle, with a large coupling to the Higgs. Of particular interest is a light, and highly mixed, stop, which we show can provide the required alterations to the combination of gg and gamma gamma widths.

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Blobrana


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RE: Special unitary group SU(2)
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In the Standard Model, the W± and Z0 bosons, and the photon, are produced by the spontaneous symmetry breaking of the electroweak symmetry from SU(2) × U(1)Y to U(1)em, caused by the Higgs mechanism. U(1)Y and U(1)em are different copies of U(1); the generator of U(1)em is given by Q = Y/2 + I3, where Y is the generator of U(1)Y (called the weak hypercharge), and I3 is one of the SU(2) generators (a component of weak isospin).
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Ed ~ W± and Z0 bosons acquire mass, and photons become massless



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Blobrana


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Posts: 131433
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Doublet-triplet splitting problem

In particle physics, the doublet-triplet (splitting) problem is a problem of some Grand Unified Theories, such as SU(5), SO(10), . Grand unified theories predict Higgs bosons (doublets of SU(2)) arise from representations of the unified group that contain other states, in particular, states that are triplets of colour. The primary problem with these colour triplet Higgs, is that they can mediate proton decay in supersymmetric theories that are only suppressed by two powers of GUT scale (i.e. they are dimension 5 supersymmetric operators). In addition to mediating proton decay, they alter gauge coupling unification. The doublet-triplet problem is the question 'what keeps the doublets light while the triplets are heavy?'
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