26 research outputs found
Fluxes in F-theory Compactifications on Genus-One Fibrations
We initiate the construction of gauge fluxes in F-theory compactifications on
genus-one fibrations which only have a multi-section as opposed to a section.
F-theory on such spaces gives rise to discrete gauge symmetries in the
effective action. We generalize the transversality conditions on gauge fluxes
known for elliptic fibrations by taking into account the properties of the
available multi-section. We test these general conditions by constructing all
vertical gauge fluxes in a bisection model with gauge group SU(5) x Z2. The
non-abelian anomalies are shown to vanish. These flux solutions are dynamically
related to fluxes on a fibration with gauge group SU(5) x U(1) by a conifold
transition. Considerations of flux quantization reveal an arithmetic constraint
on certain intersection numbers on the base which must necessarily be satisfied
in a smooth geometry. Combined with the proposed transversality conditions on
the fluxes these conditions are shown to imply cancellation of the discrete Z2
gauge anomalies as required by general consistency considerations.Comment: 30 pages; v2: typos correcte
Discrete Gauge Symmetries by Higgsing in four-dimensional F-Theory Compactifications
We study F-Theory compactifications to four dimensions that exhibit discrete
gauge symmetries. Geometrically these arise by deforming elliptic fibrations
with two sections to a genus-one fibration with a bi-section. From a
four-dimensional field-theory perspective they are remnant symmetries from a
Higgsed U(1) gauge symmetry. We implement such symmetries in the presence of an
additional SU(5) symmetry and associated matter fields, giving a geometric
prescription for calculating the induced discrete charge for the matter curves
and showing the absence of Yukawa couplings that are forbidden by this charge.
We present a detailed map between the field theory and the geometry, including
an identification of the Higgs field and the massless states before and after
the Higgsing. Finally we show that the Higgsing of the U(1) induces a G-flux
which precisely accounts for the change in the Calabi-Yau Euler number so as to
leave the D3 tadpole invariant.Comment: 30 pages; v2: substantially improved presentation, refs added; v3:
refs. added, appendix A on remnant discrete subgroups included; v4: refs.
adde
On Discrete Symmetries and Torsion Homology in F-Theory
We study the relation between discrete gauge symmetries in F-theory
compactifications and torsion homology on the associated Calabi-Yau manifold.
Focusing on the simplest example of a symmetry, we show that
there are two physically distinct ways that such a discrete gauge symmetry can
arise. First, compactifications of M-Theory on Calabi-Yau threefolds which
support a genus-one fibration with a bi-section are known to be dual to
six-dimensional F-theory vacua with a gauge symmetry. We show
that the resulting five-dimensional theories do not have a
symmetry but that the latter emerges only in the F-theory decompactification
limit. Accordingly the genus-one fibred Calabi-Yau manifolds do not exhibit
discrete torsion. Associated to the bi-section fibration is a Jacobian
fibration which does support a section. Compactifying on these related but
distinct varieties does lead to a symmetry in five dimensions
and, accordingly, we find explicitly an associated discrete torsion. We
identify the expected particle and membrane system of the discrete symmetry in
terms of wrapped M2 and M5 branes and present a field-theory description of the
physics for both cases in terms of circle reductions of six-dimensional
theories. Our results and methods generalise straightforwardly to larger
discrete symmetries and to four-dimensional compactifications.Comment: 12 pages in 2-column style, 4 figures; v2: references adde
Mordell-Weil Torsion and the Global Structure of Gauge Groups in F-theory
We study the global structure of the gauge group of F-theory compactified
on an elliptic fibration . The global properties of are encoded in the
torsion subgroup of the Mordell-Weil group of rational sections of .
Generalising the Shioda map to torsional sections we construct a specific
integer divisor class on as a fractional linear combination of the
resolution divisors associated with the Cartan subalgebra of . This divisor
class can be interpreted as an element of the refined coweight lattice of the
gauge group. As a result, the spectrum of admissible matter representations is
strongly constrained and the gauge group is non-simply connected. We exemplify
our results by a detailed analysis of the general elliptic fibration with
Mordell-Weil group and as well as a further
specialization to . Our analysis exploits the
representation of these fibrations as hypersurfaces in toric geometry.Comment: 42 pages, 10 figures; v2: references adde
Discrete Structures in F-theory Compactifications
In this thesis we study global properties of F-theory compactifications on elliptically and genus-one
fibered Calabi-Yau varieties. This is motivated by phenomenological considerations as well as by
the need for a deeper understanding of the set of consistent F-theory vacua. The global geometric
features arise from discrete and arithmetic structures in the torus fiber and can be studied in detail
for fibrations over generic bases.
In the case of elliptic fibrations we study the role of the torsion subgroup of the Mordell-Weil
group of sections in four dimensional compactifications. We show how the existence of a torsional
section restricts the admissible matter representations in the theory. This is shown to be equivalent
to inducing a non-trivial fundamental group of the gauge group.
Compactifying F-theory on genus-one fibrations with multisections gives rise to discrete selection
rules. In field theory the discrete symmetry is a broken U(1) symmetry. In the geometry the higgsing
corresponds to a conifold transition. We explain in detail the origin of the discrete symmetry from
two different M-theory phases and put the result into the context of torsion homology. Finally we
systematically construct consistent gauge
uxes on genus-one fibrations and show that these induce
an anomaly free chiral spectrum
Effect of electric current annealing in phase transition of Mn-Al alloy
The electronic structure of any material can be modified when it is exposed to high density electric currents or high strength electric fields, caused by the increased electronic/ionic mobility. Electromigration effects can have desirable uses (1), but also be a problem, for example in IC circuit design (2). However, the increased electronic/ionic mobility can be used to tailor the material properties by modifying e.g. phase formation, phase stability, density of defects etc. Our goal is to understand, by theoretical (DFT calculation) and experimental approaches, and utilize these effects in the processing of hard magnetic materials and to quantify the influence of the electric current on microstructure and magnetic properties.
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