28,167 research outputs found
Grand Unification and Time Variation of the Gauge Couplings
Astrophysical indications that the fine structure constant is time dependent
are discussed in the framework of grand unification models. A variation of the
electromagnetic coupling constant could either be generated by a corresponding
time variation of the unified coupling constant or by a time variation of the
unification scale, or by both. The case in which the time variation of the
electromagnetic coupling constant is caused by a time variation of the
unification scale is of special interest. It is supported in addition by recent
hints towards a time change of the proton-electron mass ratio. Possible
implications for baryogenesis are discussed.Comment: talk given at the 10th International Conference on Supersymmetry and
Unification of Fundamental Interactions (SUSY02), Hamburg, Germany, 17-23
June 200
Symmetry Breaking and Time Variation of the QCD Coupling
Astrophysical indications that the fine structure constant has undergone a
small time variation during the cosmological evolution are discussed within the
framework of the standard model of the electroweak and strong interactions and
of grand unification. A variation of the electromagnetic coupling constant
could either be generated by a corresponding time variation of the unified
coupling constant or by a time variation of the unification scale, of by both.
The various possibilities, differing substantially in their implications for
the variation of low energy physics parameters like the nuclear mass scale, are
discussed. The case in which the variation is caused by a time variation of the
unification scale is of special interest. It is supported in addition by recent
hints towards a time change of the proton-electron mass ratio.Comment: 5 page
The crucial problem: the electroweak symmetry breaking
1. Why we do Believe in the Standard Model
2. Why we do not Believe in the Standard Model
2.1 Conceptual Problems
2.2 Hints from Experiment
2.2.1 Unification of Couplings
2.2.2 Dark Matter
2.2.3 Neutrino Masses
2.2.4 Baryogenesis
3. Status of the Search for the Higgs and for New Physics
4. ConclusionComment: 16 pages, Talk, XI Rencontres de Blois, Frontiers of Matter, 27
June-3 July 199
Symmetry Breaking and Time Variation of Gauge Couplings
Astrophysical indications that the fine structure constant has undergone a
small time variation during the cosmological evolution are discussed within the
framework of the standard model of the electroweak and strong interactions and
of grand unification. A variation of the electromagnetic coupling constant
could either be generated by a corresponding time variation of the unified
coupling constant or by a time variation of the unification scale, of by both.
The various possibilities, differing substantially in their implications for
the variation of low energy physics parameters like the nuclear mass scale, are
discussed. The case in which the variation is caused by a time variation of the
unification scale is of special interest. It is supported in addition by recent
hints towards a time change of the proton-electron mass ratio. Implications for
the analysis of the Oklo remains and for quantum optics tests are discussed.Comment: 9 page
Does the QCD Scale vary in time?
Last year I talked at this meeting about a possible time dependence of the
QCD coupling constant . This year I shall look into the problem once
more, without fully repeating the arguments given last year. Astrophysical
indications that the fine structure constant has undergone a small time
variation during the cosmological evolution are discussed within the framework
of the standard model of the electroweak and strong interactions and of grand
unification. A variation of the electromagnetic coupling constant could either
be generated by a corresponding time variation of the unified coupling constant
or by a time variation of the unification scale, or by both. The various
possibilities, differing substantially in their implications for the variation
of low energy physics parameters like the nuclear mass scale, are discussed.
The case in which the variation is caused by a time variation of the
unification scale is of special interest. It is supported in addition by recent
hints towards a time change of the proton-electron mass ratio.Comment: 5 pages, QCD International Conference Montpellier 2-9 July 200
Understanding SUSY limits from LEP
LEP results have constrained heavily the Minimal Supersymmetric Standard
Model, while providing hints for light Higgs boson and for ``SUSY-assisted''
gauge couling unification. In this paper the results obtained at LEP within two
scenarios, the gravity-mediated MSSM framework and the minimal SUGRA scenario
are presented. Model-dependence and coverage of LEP results is discussed.Comment: Prepared for 3nd International Conference on Physics Beyond the
Standard Model, Beyond the Desert 02, Oulu, Finland, 2-7 June 200
The Intermediate Scale MSSM, the Higgs Mass and F-theory Unification
Even if SUSY is not present at the Electro-Weak scale, string theory suggests
its presence at some scale M_{SS} below the string scale M_s to guarantee the
absence of tachyons. We explore the possible value of M_{SS} consistent with
gauge coupling unification and known sources of SUSY breaking in string theory.
Within F-theory SU(5) unification these two requirements fix M_{SS} ~ 5 x
10^{10} GeV at an intermediate scale and a unification scale M_c ~ 3 x 10^{14}
GeV. As a direct consequence one also predicts the vanishing of the quartic
Higgs SM self-coupling at M_{SS} ~10^{11} GeV. This is tantalizingly consistent
with recent LHC hints of a Higgs mass in the region 124-126 GeV. With such a
low unification scale M_c ~ 3 x 10^{14} GeV one may worry about too fast proton
decay via dimension 6 operators. However in the F-theory GUT context SU(5) is
broken to the SM via hypercharge flux. We show that this hypercharge flux
deforms the SM fermion wave functions leading to a suppression, avoiding in
this way the strong experimental proton decay constraints. In these
constructions there is generically an axion with a scale of size f_a ~
M_c/(4\pi)^2 ~ 10^{12} GeV which could solve the strong CP problem and provide
for the observed dark matter. The prize to pay for these attractive features is
to assume that the hierarchy problem is solved due to anthropic selection in a
string landscape.Comment: 48 pages, 8 figures. v3: further minor correction
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