In General > s.a. symmetry
breaking; types of Yang-Mills theories; unification.
* History: 1974, Idea proposed by Georgi and Glashow.
* Idea: Theories that
unify the electroweak and strong interactions, usually described by a (Yang-Mills)
gauge theory, where the interaction is mediated by
a connection/potential
belonging to (the Lie algebra of) a single group; Gravity
is still not included in the unification.
* Structure: Like other
gauge theories, they are based on a principal fiber bundle over spacetime (suitably
compactified from boundary conditions),
with a certain structure group G, and
the quarks and leptons are described by a cross section of appropriate associated
vector bundles; The interactions are mediated by connections, which are determined
by the critical points of action integrals constructed as spacetime integrals
of the curvature and its Hodge dual.
* Gauge group: Several
groups have been proposed as strong candidates for grand unification, in particular
SU(5), now known to be inadequate (1994); SO(10); Exceptional groups like E6,
which could come from the E8 of string theory,
E7, and E8.
* Symmetry breaking: All of the above are assumed to break to SU(3)
SU(2)
U(1)
SU(3)
U(1).
@ Reviews: Georgi SA(81)apr; Langacker PRP(81).
@ Textbooks: Cline & Mills 78; Zee 82; Ross 84; Kounnas et al 85.
@ Models: Georgi & Glashow PRL(74)
[SU(5)]; Maraner MPLA(04)ht/03 [spacetime
extensions of SO(10)]; Dorsner & Fileviez Pérez NPB(05)hp [non-susy
SU(5)].
> Online resources: Wikipedia page.
Phenomenology > s.a. inflation
scenarios; neutrino; monopoles.
* Motivation: (i) Observed family-structure; (ii) Meeting of the gauge
couplings; (iii) Neutrino oscillations; (iv) The intricate pattern of masses
and mixings of all fermions, including neutrinos; and (v) Need for B-L as
a generator, to implement baryogenesis.
* Indications: 2000, Evidence favors grand unification along a particular
route, based on the ideas of supersymmetry, SU(4)-color and left-right symmetry;
thus it points to the relevance of an effective string-unified G(224)
or SO(10)-symmetry.
* Successes: Prediction
of sin2
W to
within 5%; Elegant classification of particles.
* Problems: Quark/lepton
mass ratios; Proton decay.
* Leptoquark: A hypothetical
particle that turns quarks into leptons and vice versa, which arises naturally
in GUT's; Depending on the model, they may form a singlet, a doublet, or a
triplet (one particle may have charge +2/3, another –1/3); Their masses are
estimated to be at least in the hundreds of GeV; If they exist, they may offer
an explanation for the NuTeV anomaly in neutrino physics, and the LHC will
search for them..
@ Coupling constants: Bennet & Nielsen IJMPA(94).
@ Cosmology: Singh FdP(83); Dorsner et al NPB(06).
Proton Decay > s.a. particle
types.
* Decay modes: The dominant one may be
-bar K+,
with
+K0 being
another possibility.
* Lifetime: In a typical
(non-susy) version of GUT, the lifetime is predicted around 5
1029 yr,
while experimentally one gets
> 1030 yr
and 5
1031–5
1032 yr
for neutrino and neutrinoless decays, respectively; A conservative estimate
is about 1
1034 yr.
* Status: 1998,
1.6
1033 yr,
from Superkamiokande [@ Shiozawa et al PRL(98)].
@ References: Goldhaber et al Sci(80)nov*;
Weinberg SA(81)jun; Sulak AS(82); Pati hp/00;
Dorsner
& Fileviez Pérez PLB(05)hp/04 [upper
bound on lifetime]; Frampton MPLA(07)
[in teravolt unification].
Beyond Regular GUTS > s.a. action
for general relativity; cosmic
strings; kaluza-klein;
particle physics.
* Supersymmetric GUTs:
Adding susy extende proton lifetime, among other benefits; > s.a. supersymmetric
theories.
@ Supersymmetric GUTs: Sakellariadou & Rocher hp/04-in,
Rocher & Sakellariadou JCAP(05)
[and cosmic strings]; Mondragón & Zoupanos SIGMA(08)-a0802 [reduction
of couplings].
@ And brane world:
Duff IJMPA(01)ht/00-in;
Berenstein ht/06.
@ And strings: Pati IJMPD(06).
@ Non-commutative: Aschieri
et al NPB(03)ht/02;
Calmet EPJC(07)
[non-commutative spacetime].
@ Generalized: Froggatt et al NPB(94)
[anti-grand unification, and fermion masses]; Spaans gq/97 [topological];
Chaves & Morales MPLA(00)ht/99 [with
generalized Yang-Mills].
Main page – Abbreviations – Journals – Comments – Other
sites – Acknowledgements
Send feedback and suggestions to bombelli at olemiss.edu – Modified
20 jun 2008