196 research outputs found
Mirror Mediation
I show that the effective action of string compactifications has a structure
that can naturally solve the supersymmetric flavour and CP problems. At leading
order in the g_s and \alpha' expansions, the hidden sector factorises. The
moduli space splits into two mirror parts that depend on Kahler and complex
structure moduli. Holomorphy implies the flavour structure of the Yukawa
couplings arises in only one part. In type IIA string theory flavour arises
through the Kahler moduli sector and in type IIB flavour arises through the
complex structure moduli sector. This factorisation gives a simple solution to
the supersymmetric flavour and CP problems: flavour physics is generated in one
sector while supersymmetry is broken in the mirror sector. This mechanism does
not require the presence of gauge, gaugino or anomaly mediation and is
explicitly realised by phenomenological models of IIB flux compactifications.Comment: 33 pages, 1 figure; v2: typos, references, minor correction
The QCD Axion and Moduli Stabilisation
We investigate the conditions for a QCD axion to coexist with stabilised
moduli in string compactifications. We show how the simplest approaches to
moduli stabilisation give unacceptably large masses to the axions. We observe
that solving the F-term equations is insufficient for realistic moduli
stabilisation and give a no-go theorem on supersymmetric moduli stabilisation
with unfixed axions applicable to all string compactifications and relevant to
much current work. We demonstrate how nonsupersymmetric moduli stabilisation
with unfixed axions can be realised. We finally outline how to stabilise the
moduli such that f_a is within the allowed window 10^9 GeV < f_a < 10^{12} GeV,
with f_a ~ \sqrt{M_{SUSY} M_P}.Comment: 36 pages; v2: extended discussion of cosmological bound on f_a,
references added, version accepted by journal; v3. factor of 2 correcte
The de Sitter swampland conjecture and supersymmetric AdS vacua
It has recently been conjectured that string theory does not admit de Sitter
critical points. This note points out that in several cases, including KKLT or
racetrack models, this statement is equivalent to the absence of supersymmetric
Minkowski or AdS solutions. This equivalence arises from establishing the
positivity of the potential in a large-radius limit, requiring a turnover of
the potential before reaching an AdS vacuum. For example, this conjecture is
incompatible with the simplest 1-modulus KKLT AdS supersymmetric solution.Comment: Prepared for submission to Int. Journ. Mod. Phys. A; v2. added
references and more discussio
On Gauge Threshold Corrections for Local IIB/F-theory GUTs
We study gauge threshold corrections for local GUT models in IIB/F-theory.
Consistency with holomorphy requirements of supergravity and the
Kaplunovsky-Louis formula implies that the unification scale is enhanced by the
bulk radius R from the string scale to M_X =RM_S. We argue that the stringy
interpretation of this is via a locally uncancelled tadpole sourced by the
hypercharge flux. This sources closed string modes propagating into the bulk;
equivalently open string gauge coupling running up to the winding scale M_X.
The enhancement to R M_s is tied to GUT breaking by a globally trivial
hypercharge flux and will occur in all models realising this mechanism.Comment: 4 pages; v2. journal versio
On the Explicit Construction and Statistics of Calabi-Yau Flux Vacua
We explicitly construct and study the statistics of flux vacua for type IIB
string theory on an orientifold of the Calabi-Yau hypersurface
, parametrised by two relevant complex structure moduli. We
solve for these moduli and the dilaton field in terms of the set of integers
defining the 3-form fluxes and examine the distribution of vacua. We compare
our numerical results with the predictions of the Ashok-Douglas density , finding good overall agreement in different regions of moduli
space. The number of vacua are found to scale with the distance in flux space.
Vacua cluster in the region close to the conifold singularity. Large
supersymmetry breaking is more generic but supersymmetric and hierarchical
supersymmetry breaking vacua can also be obtained. In particular, the small
superpotentials and large dilaton VEVs needed to obtain de Sitter space in a
controllable approximation are possible but not generic. We argue that in a
general flux compactification, the rank of the gauge group coming from D3
branes could be statistically preferred to be very small.Comment: 26 pages, 9 figures; v2: references adde
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