9 research outputs found
Hermitian Yang-Mills instantons on Calabi-Yau cones
We study and construct non-abelian hermitian Yang-Mills (HYM) instantons on
Calabi-Yau cones. By means of a particular isometry preserving ansatz, the HYM
equations are reduced to a novel Higgs-Yang-Mills flow on the Einstein-Kahler
base. For any 2d-dimensional Calabi-Yau cone, we find explicit solutions of the
flow equations that correspond to non-trivial SU(d) HYM instantons. These can
be regarded as deformations of the spin connection of the Calabi-Yau cone.Comment: 17 page
Local SU(5) Unification from the Heterotic String
We construct a 6D supergravity theory which emerges as intermediate step in
the compactification of the heterotic string to the supersymmetric standard
model in four dimensions. The theory has N=2 supersymmetry and a gravitational
sector with one tensor and two hypermultiplets in addition to the supergravity
multiplet. Compactification to four dimensions occurs on a T^2/Z_2 orbifold
which has two inequivalent pairs of fixed points with unbroken SU(5) and
SU(2)xSU(4) symmetry, respectively. All gauge, gravitational and mixed
anomalies are cancelled by the Green-Schwarz mechanism. The model has partial
6D gauge-Higgs unification. Two quark-lepton generations are localized at the
SU(5) branes, the third family is composed of split bulk hypermultiplets. The
top Yukawa coupling is given by the 6D gauge coupling, all other Yukawa
couplings are generated by higher-dimensional operators at the SU(5) branes.
The presence of the SU(2)xSU(4) brane breaks SU(5) and generates split gauge
and Higgs multiplets with N=1 supersymmetry in four dimensions. The third
generation is obtained from two split \bar{5}-plets and two split 10-plets,
which together have the quantum numbers of one \bar{5}-plet and one 10-plet.
This avoids unsuccessful SU(5) predictions for Yukawa couplings of ordinary 4D
SU(5) grand unified theories.Comment: 38 pages. v2: Typos correcte
Fermions in Kaluza-Klein and Randall-Sundrum Theories
The Kaluza-Klein theory and Randall-Sundrum theory are examined
comparatively, with focus on the behavior of the five dimensional (Dirac)
fermion in the dimensional reduction to four dimensions. They are properly
treated using the Cartan formalism. In the KK case, the dual property between
the electric and magnetic dipole moments is revealed in relation to the ratio
of two massive parameters: the inverse of the radius of the extra-space circle
and the 5D fermion mass. The order estimation of the couplings is done. In the
RS case, we consider the interaction with the 5D(bulk) Higgs field and the
gauge field. The chiral property, localization, anomaly phenomena are examined.
We evaluate the bulk quantum effect using the method of the induced effective
action. The electric dipole moment term naturally appears. This is a new origin
of the CP-violation. In the 4D limit, the dual relation between KK model and RS
model appears.Comment: 30 pages, 4 figures, Typographical errors are correcte
Corrections to flat-space particle dynamics arising from space granularity
The construction of effective Hamiltonians describing corrections to flat
space particle dynamics arising from the granularity of space at very short
distances is discussed in the framework of an heuristic approach to the
semiclassical limit of loop quantum gravity. After some general motivation of
the subject, a brief non-specialist introduction to the basic tools employed in
the loop approach is presented. The heuristical semiclassical limit is
subsequently defined and the application to the case of photons and spin 1/2
fermions is described. The resulting modified Maxwell and Dirac Hamiltonians,
leading in particular to Planck scale corrections in the energy-momentum
relations, are presented. Alternative interpretations of the results and their
limitations, together with other approaches are briefly discussed along the
text. Three topics related to the above methods are reviewed: (1) The
determination of bounds to the Lorentz violating parameters in the fermionic
sector, obtained from clock comparison experiments.(2) The calculation of
radiative corrections in preferred frames associated to space granularity in
the framework of a Yukawa model for the interactions and (3) The calculation of
synchrotron radiation in the framework of the Myers-Pospelov effective theories
describing Lorentz invariance violations, as well as a generalized approach to
radiation in Planck scale modified electrodynamics. The above exploratory
results show that quantum gravity phenomenology provides observational guidance
in the construction of quantum gravity theories and opens up the possibility of
probing Planck scale physics.Comment: 49 pages, 6 figures and 4 tables. Extended version of the talk given
at the 339-th WE-Heraeus-Seminar: Special Relativity, will it survive the
next 100 years?, Potsdam, february 200