70 research outputs found
On the Possibility of Large Axion Moduli Spaces
We study the diameters of axion moduli spaces, focusing primarily on type IIB
compactifications on Calabi-Yau three-folds. In this case, we derive a
stringent bound on the diameter in the large volume region of parameter space
for Calabi-Yaus with simplicial K\"ahler cone. This bound can be violated by
Calabi-Yaus with non-simplicial K\"ahler cones, but additional contributions
are introduced to the effective action which can restrict the field range
accessible to the axions. We perform a statistical analysis of simulated moduli
spaces, finding in all cases that these additional contributions restrict the
diameter so that these moduli spaces are no more likely to yield successful
inflation than those with simplicial K\"ahler cone or with far fewer axions.
Further heuristic arguments for axions in other corners of the duality web
suggest that the difficulty observed in hep-th/0303252 of finding an axion
decay constant parametrically larger than applies not only to individual
axions, but to the diagonals of axion moduli space as well. This observation is
shown to follow from the weak gravity conjecture of hep-th/0601001, so it
likely applies not only to axions in string theory, but also to axions in any
consistent theory of quantum gravity.Comment: 26+11 pages, 9 figures, discussion of relationship to weak gravity
conjecture added v2, references added v3, minor changes v4, matches
publication versio
Evidence for C-theorems in 6D SCFTs
Using the recently established classification of 6D SCFTs we present evidence
for the existence of families of weak C-functions, that is, quantities which
decrease in a flow from the UV to the IR. Introducing a background R-symmetry
field strength R and a non-trivial tangent bundle T on the 6D spacetime, we
consider C-functions given by the linear combinations C = m1 alpha + m2 beta +
m3 gamma, where alpha, beta and gamma are the anomaly polynomial coefficients
for the formal characteristic classes c2(R)^2, c2(R)p1(T) and p1(T)^2. By
performing a detailed sweep over many theories, we determine the shape of the
unbounded monotonic region in "m-space" compatible with both Higgs branch flows
and tensor branch flows. We also verify that --as expected-- the Euler density
conformal anomaly falls in the admissible region.Comment: v2: 25 pages, 9 figures, typos correcte
Evidence for a Lattice Weak Gravity Conjecture
The Weak Gravity Conjecture postulates the existence of superextremal charged
particles, i.e. those with mass smaller than or equal to their charge in Planck
units. We present further evidence for our recent observation that in known
examples a much stronger statement is true: an infinite tower of superextremal
particles of different charges exists. We show that effective Kaluza-Klein
field theories and perturbative string vacua respect the Sublattice Weak
Gravity Conjecture, namely that a finite index sublattice of the full charge
lattice exists with a superextremal particle at each site. In perturbative
string theory we show that this follows from modular invariance. However, we
present counterexamples to the stronger possibility that a superextremal
particle exists at every lattice site, including an example in which the
lightest charged particle is subextremal. The Sublattice Weak Gravity
Conjecture has many implications both for abstract theories of quantum gravity
and for real-world physics. For instance, it implies that if a gauge group with
very small coupling exists, then the fundamental gravitational cutoff
energy of the theory is no higher than .Comment: v2: 41 pages, typos fixed, references added, substantial revisions
and clarifications (conclusions unchanged
The Weak Gravity Conjecture and Emergence from an Ultraviolet Cutoff
We study ultraviolet cutoffs associated with the Weak Gravity Conjecture
(WGC) and Sublattice Weak Gravity Conjecture (sLWGC). There is a magnetic WGC
cutoff at the energy scale with an associated sLWGC tower of
charged particles. A more fundamental cutoff is the scale at which gravity
becomes strong and field theory breaks down entirely. By clarifying the nature
of the sLWGC for nonabelian gauge groups we derive a parametric upper bound on
this strong gravity scale for arbitrary gauge theories. Intriguingly, we show
that in theories approximately saturating the sLWGC, the scales at which loop
corrections from the tower of charged particles to the gauge boson and graviton
propagators become important are parametrically identical. This suggests a
picture in which gauge fields emerge from the quantum gravity scale by
integrating out a tower of charged matter fields. We derive a converse
statement: if a gauge theory becomes strongly coupled at or below the quantum
gravity scale, the WGC follows. We sketch some phenomenological consequences of
the UV cutoffs we derive.Comment: 50 pages, 5 figures. v2: references added, clarified remarks about
Higgsin
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