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Large field ranges from aligned and misaligned winding
We search for effective axions with super-Planckian decay constants in type
IIB string models. We argue that such axions can be realised as long winding
trajectories in complex-structure moduli space by an appropriate flux choice.
Our main findings are: The simplest models with aligned winding in a 2-axion
field space fail due to a general no-go theorem. However, equally simple models
with misaligned winding, where the effective axion is not close to any of the
fundamental axions, appear to work to the best of our present understanding.
These models have large decay constants but no large monotonic regions in the
potential, making them unsuitable for large-field inflation. We also show that
our no-go theorem can be avoided by aligning three or more axions. We argue
that, contrary to misaligned models, such models can have both large decay
constants and large monotonic regions in the potential. Our results may be used
to argue against the refined Swampland Distance Conjecture and strong forms of
the axionic Weak Gravity Conjecture. It becomes apparent, however, that
realising inflation is by far harder than just producing a light field with
large periodicity
Color transparency in deeply inelastic diffraction
We suggest a simple physical picture for the diffractive parton distributions
that appear in diffractive deeply inelastic scattering. In this picture,
partons impinging on the proton can have any transverse separation, but only
when the separation is small can they penetrate the proton without breaking it
up. By comparing the predictions from this picture with the diffractive data
from HERA, we determine rough values for the small separations that dominate
the diffraction process.Comment: 10 pages, 2 figures; v2: citations added, two comments revised and
expanded, results unchange
Proton Decay in Supersymmetric GUT Models
The instability of protons is a crucial prediction of supersymmetric GUTs. We
review the decay in minimal supersymmetric SU(5), which is dominated by
dimension-five operators, and discuss the implications of the failure of Yukawa
unification for the decay rate. In a consistent SU(5) model, where SU(5)
relations among Yukawa couplings hold, the proton decay rate can be several
orders of magnitude smaller than the present experimental bound. Finally, we
discuss orbifold GUTs, where proton decay via dimension-five operators is
absent. The branching ratios of dimension-six decay can significantly differ
from those in four dimensions.Comment: DESY report number correcte
Anomalies on orbifolds with gauge symmetry breaking
We embed two 4D chiral multiplets of opposite representations in the 5D N=2
gauge theory compactified on an orbifold .
There are two types of orbifold boundary conditions in the extra dimension to
obtain the 4D N=1 gauge theory from the bulk: in
Type I, one has the bulk gauge group at and the unbroken gauge group at
while in Type II, one has the unbroken gauge group at both fixed
points. In both types of orbifold boundary conditions, we consider the zero
mode(s) as coming from a bulk -plet and brane fields at the fixed
point(s) with the unbroken gauge group. We check the consistency of this
embedding of fields by the localized anomalies and the localized FI terms. We
show that the localized anomalies in Type I are cancelled exactly by the
introduction of a bulk Chern-Simons term. On the other hand, in some class of
Type II, the Chern-Simons term is not enough to cancel all localized anomalies
even if they are globally vanishing. We also find that for the consistent
embedding of brane fields, there appear only the localized log FI terms at the
fixed point(s) with a U(1) factor.Comment: LaTeX file of 19 pages with no figure, published versio
The MSSM from Scherk-Schwarz Supersymmetry Breaking
We present a five-dimensional model compactified on an interval where
supersymmetry is broken by the Scherk-Schwarz mechanism. The gauge sector
propagates in the bulk, two Higgs hypermultiplets are quasilocalized, and quark
and lepton multiplets localized, in one of the boundaries. The effective
four-dimensional theory is the MSSM with very heavy gauginos, heavy squarks and
light sleptons and Higgsinos. The soft tree-level squared masses of the Higgs
sector can be negative and they can (partially) cancel the positive one-loop
contributions from the gauge sector. Electroweak symmetry breaking can then
comfortably be triggered by two-loop radiative corrections from the top-stop
sector. The fine tuning required to obtain the electroweak scale is found to be
much smaller than in the MSSM, with essentially no fine-tuning for few TeV
gaugino masses. All bounds from direct Higgs searches at LEP and from
electroweak precision observables can be satisfied. The lightest supersymmetric
particle is a (Higgsino-like) neutralino that can accomodate the abundance of
Dark Matter consistently with recent WMAP observations.Comment: 23 pages, 3 figure
Non-commutative Euclidean structures in compact spaces
Based on results for real deformation parameter q we introduce a compact non-
commutative structure covariant under the quantum group SOq(3) for q being a
root of unity. To match the algebra of the q-deformed operators with necesarry
conjugation properties it is helpful to define a module over the algebra
genera- ted by the powers of q. In a representation where X is diagonal we show
how P can be calculated. To manifest some typical properties an example of a
one-di- mensional q-deformed Heisenberg algebra is also considered and compared
with non-compact case.Comment: Changed conten
Energy Transfer between Throats from a 10d Perspective
Strongly warped regions, also known as throats, are a common feature of the
type IIB string theory landscape. If one of the throats is heated during
cosmological evolution, the energy is subsequently transferred to other throats
or to massless fields in the unwarped bulk of the Calabi-Yau orientifold. This
energy transfer proceeds either by Hawking radiation from the black hole
horizon in the heated throat or, at later times, by the decay of
throat-localized Kaluza-Klein states. In both cases, we calculate in a 10d
setup the energy transfer rate (respectively decay rate) as a function of the
AdS scales of the throats and of their relative distance. Compared to existing
results based on 5d models, we find a significant suppression of the energy
transfer rates if the size of the embedding Calabi-Yau orientifold is much
larger than the AdS radii of the throats. This effect can be partially
compensated by a small distance between the throats. These results are
relevant, e.g., for the analysis of reheating after brane inflation. Our
calculation employs the dual gauge theory picture in which each throat is
described by a strongly coupled 4d gauge theory, the degrees of freedom of
which are localized at a certain position in the compact space.Comment: 25 pages; a comment adde
Running Coupling with Minimal Length
In models with large additional dimensions, the GUT scale can be lowered to
values accessible by future colliders. Due to modification of the loop
corrections from particles propagating into the extra dimensions, the
logarithmic running of the couplings of the Standard Model is turned into a
power law. These loop-correction are divergent and the standard way to achieve
finiteness is the introduction of a cut-off. The question remains, whether the
results are reliable as they depend on an unphysical parameter.
In this paper, we show that this running of the coupling can be calculated
within a model including the existence of a minimal length scale. The minimal
length acts as a natural regulator and allows us to confirm cut-off
computations.Comment: 26 pages, 5 figures, typos corrected, replaced with published versio
Family Unification on an Orbifold
We construct a family-unified model on a Z_2xZ_2 orbifold in five dimensions.
The model is based on a supersymmetric SU(7) gauge theory. The gauge group is
broken by orbifold boundary conditions to a product of grand unified SU(5) and
SU(2)xU(1) flavor symmetry. The structure of Yukawa matrices is generated by an
interplay between spontaneous breaking of flavor symmetry and geometric factors
arising due to field localization in the extra dimension.Comment: 13 page
Generalized Froggatt-Nielsen Mechanism
In this paper, we propose a Generalized Froggatt-Nielsen mechanism in which
non-renormalizable operators involving a GUT group and non-singlet
Higgs field are introduced. Thus the GUT gauge symmetry breaking and the
generation of hierarchical flavor hierarchy have a common origin in this
mechanism. In this Generalized Froggatt-Nielsen mechanism, we propose
universality conditions for coefficients corresponding to different
contractions in the group productions. We find that the predictions in
Generalized Froggatt-Nielsen mechanism for SU(5) GUT is different to that of
ordinary Froggatt-Nielsen mechanism. Such Generalized Froggatt-Nielsen
mechanism can be used in GUT models when ordinary Froggatt-Nielsen mechanism is
no longer available. We study the application of Generalized Froggatt-Nielsen
mechanism in SO(10) model. We find that realistic standard model mass hierarchy
and mixings can be obtained both in SU(5) and SO(10) GUT models with such
Generalized Froggatt-Nielsen mechanism.Comment: 4 pages, no figure
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