1,988 research outputs found
Background Symmetries In Orbifolds With Discrete Wilson Lines
Target space symmetries are studied for orbifold compactified string theories
containing Wilson line background fields. The symmetries determined are for
those moduli which contribute to the string loop threshold corrections of the
gauge coupling constants. The groups found are subgroups of the modular group
and depend on the choice of discrete Wilson lines and the shape of
the underlying six-dimensional lattice.Comment: 31 pages, QMW--TH--94/0
Urban freight logistics in the European Union
The paper recalls the main challenges of the European urban freight policy: the environment, the need
for sustainable growth and quality of urban life. These are then interpreted by the member states. Some
states have a top down prescriptive approach some others do not. The BESTUFS project, promoted by the
EC, collects and disseminates best practice across the EU. It has identified a deep weakness at a local
level, whilst also a wide range of pilots and successful exceptions
Gauge Coupling Constant Unification With Planck Scale Values Of Moduli
Convergence of the standard model gauge coupling constants to a common value
at around GeV is studied in the context of orbifold theories
where the modular symmetry groups for and moduli are broken to
subgroups of . The values of the moduli required for this
unification of coupling constants are studied for this case and also for the
case where string unification is accompanied by unification to a gauge group
larger then Comment: Tex, 15 pages, minor typos corrected and some references adde
Implications of Neutrino Mass Generation from QCD Confinement
We consider the possibility that the quark condensate formed by QCD
confinement generates Majorana neutrino masses m_\nu via dimension seven
operators. No degrees of freedom beyond the Standard Model are necessary, below
the electroweak scale. Obtaining experimentally acceptable neutrino masses
requires the new physics scale \Lambda ~ TeV, providing a new motivation for
weak-scale discoveries at the LHC. We implement this mechanism using a Z_3
symmetry which leads to a massless up quark above the QCD chiral condensate
scale. We use non-helicity-suppressed light meson rare decay data to constrain
\Lambda. Experimental constraints place a mild hierarchy on the flavor
structure of dimension seven operators and the resulting neutrino mass matrix.Comment: 4 pages, Revte
Scales of Gaugino Condensation and Supersymmetry Breaking in Nonstandard M-Theory Embeddings
We investigate the formation of dynamical gaugino condensates and
supersymmetry breaking in the compactifications of Horava-Witten theory with
perturbative nonstandard embeddings. Specific models are considered where the
underlying massless charged states of the condensing sector are determined by
the spectra of and orbifolds with nonstandard
embeddings. We find among them viable examples where gaugino condensation is
triggered on the wall with the weakest gauge coupling at . In all
these cases the magnitude of the condensate formed is below the energy scales
at which extra dimensions are resolved, and so justifies the analysis of
condensation in an effective 4-dimensional framework. We make some comments
concerning the size of the largest extra dimension in the models considered. We
discuss racetrack scenarios in the framework of perturbative nonstandard
embeddings.Comment: 28 pages, 7 figures, Latex file; typos correcte
Light Gauginos - a Solution to More than the EDMs?
In this talk I want to present questions that remained unclear to me in the
last years. These questions concern the Electric Dipole Moments of electron and
neutron and the way people exclude regions of parameter space.Comment: 7 pages, 2 eps-figues included, uses espcrc2.sty, submitted to
conference proceedings for SUSY30; one error in dimensions correcte
Threshold Corrections and Symmetry Enhancement in String Compactifications
We present the computation of threshold functions for Abelian orbifold
compactifications. Specifically, starting from the massive, moduli-dependent
string spectrum after compactification, we derive the threshold functions as
target space duality invariant free energies (sum over massive string states).
In particular we work out the dependence on the continuous Wilson line moduli
fields. In addition we concentrate on the physically interesting effect that at
certain critical points in the orbifold moduli spaces additional massless
states appear in the string spectrum leading to logarithmic singularities in
the threshold functions. We discuss this effect for the gauge coupling
threshold corrections; here the appearance of additional massless states is
directly related to the Higgs effect in string theory. In addition the
singularities in the threshold functions are relevant for the loop corrections
to the gravitational coupling constants.Comment: 68 pages (equations 8.16 and 8.17 corrected; added footnotes 4,5,11
Non-perturbative monodromies in N=2 heterotic string vacua
We address non-perturbative effects and duality symmetries in heterotic
string theories in four dimensions. Specifically, we consider how each of the
four lines of enhanced gauge symmetries in the perturbative moduli space of
compactifications is split into 2 lines where monopoles and dyons
become massless. This amounts to considering non-perturbative effects
originating from enhanced gauge symmetries at the microscopic string level. We
show that the perturbative and non-perturbative monodromies consistently lead
to the results of Seiberg-Witten upon identication of a consistent truncation
procedure from local to rigid supersymmetry.Comment: 41 pages, Latex (minor changes in text and note added
GUTs in Type IIB Orientifold Compactifications
We systematically analyse globally consistent SU(5) GUT models on
intersecting D7-branes in genuine Calabi-Yau orientifolds with O3- and
O7-planes. Beyond the well-known tadpole and K-theory cancellation conditions
there exist a number of additional subtle but quite restrictive constraints.
For the realisation of SU(5) GUTs with gauge symmetry breaking via U(1)_Y flux
we present two classes of suitable Calabi-Yau manifolds defined via del Pezzo
transitions of the elliptically fibred hypersurface P_{1,1,1,6,9}[18] and of
the Quintic P_{1,1,1,1,1}[5], respectively. To define an orientifold projection
we classify all involutions on del Pezzo surfaces. We work out the model
building prospects of these geometries and present five globally consistent
string GUT models in detail, including a 3-generation SU(5) model with no
exotics whatsoever. We also realise other phenomenological features such as the
10 10 5 Yukawa coupling and comment on the possibility of moduli stabilisation,
where we find an entire new set of so-called swiss-cheese type Calabi-Yau
manifolds. It is expected that both the general constrained structure and the
concrete models lift to F-theory vacua on compact Calabi-Yau fourfolds.Comment: 138 pages, 9 figures; v2, v3: typos corrected, one reference adde
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