125 research outputs found
De Sitter Vacua from a D-term Generated Racetrack Uplift
We propose an uplift mechanism using a structure of multi-K\"ahler moduli
dependence in the F-term potential of type IIB string theory compactifications.
This mechanism requires a D-term condition that fixes one modulus to be
proportional to another modulus, resulting in a trivial D-term potential. De
Sitter minima are realized along with an enhancement of the volume in the Large
Volume Scenario and no additional suppression of the uplift term such as
warping is required. We further show the possibility to realize the uplift
mechanism in the presence of more K\"ahler moduli such that we expect the
uplift mechanism to work in many other compactifications.Comment: 20 pages, 1 figur
The 3.5 keV Line from Stringy Axions
An interesting result in particle astrophysics is the recent detection of an
unexplained 3.5 keV line from galaxy clusters. A promising model, which can
explain the morphology of the signal and its non-observation in dwarf
spheroidal galaxies, involves a 7 keV dark matter particle decaying into a pair
of ultra-light axions that convert into photons in the magnetic field of the
clusters. Given that light axions emerge naturally in 4D string vacua, in this
paper we present a microscopic realisation of this model within the framework
of type IIB flux compactifications. Dark matter is a local closed string axion
which develops a tiny mass due to subdominant poly-instanton corrections to the
superpotential and couples via kinetic mixing to an almost massless open string
axion living on a D3-brane at a singularity. The interaction of this
ultra-light axion with photons is induced by U(1) kinetic mixing. After
describing the Calabi-Yau geometry and the brane set-up, we discuss in depth
moduli stabilisation, the resulting mass spectrum and the strength of all
relevant couplings.Comment: 27 pages + appendices, 1 figure; typos corrected, references added,
additional comments on the cosmological history and DM production in the
conclusion
Point-Particle Effective Field Theory III: Relativistic Fermions and the Dirac Equation
We formulate point-particle effective field theory (PPEFT) for relativistic
spin-half fermions interacting with a massive, charged finite-sized source
using a first-quantized effective field theory for the heavy compact object and
a second-quantized language for the lighter fermion with which it interacts.
This description shows how to determine the near-source boundary condition for
the Dirac field in terms of the relevant physical properties of the source, and
reduces to the standard choices in the limit of a point source. Using a
first-quantized effective description is appropriate when the compact object is
sufficiently heavy, and is simpler than (though equivalent to) the effective
theory that treats the compact source in a second-quantized way. As an
application we use the PPEFT to parameterize the leading energy shift for the
bound energy levels due to finite-sized source effects in a model-independent
way, allowing these effects to be fit in precision measurements. Besides
capturing finite-source-size effects, the PPEFT treatment also efficiently
captures how other short-distance source interactions can shift bound-state
energy levels, such as due to vacuum polarization (through the Uehling
potential) or strong interactions for Coulomb bound states of hadrons, or any
hypothetical new short-range forces sourced by nuclei.Comment: 29 pages plus appendices, 3 figure
Failure of Perturbation Theory Near Horizons: the Rindler Example
Persistent puzzles to do with information loss for black holes have
stimulated critical reassessment of the domain of validity of semiclassical EFT
reasoning in curved spacetimes, particularly in the presence of horizons. We
argue here that perturbative predictions about evolution for very long times
near a horizon are subject to problems of secular growth - i.e. powers of small
couplings come systematically together with growing functions of time. Such
growth signals a breakdown of naive perturbative calculations of late-time
behaviour, regardless of how small ambient curvatures might be. Similar issues
of secular growth also arise in cosmology, and we build evidence for the case
that such effects should be generic for gravitational fields. In particular,
inferences using free fields coupled only to background metrics can be
misleading at very late times due to the implicit assumption they make of
perturbation theory when neglecting other interactions. Using the Rindler
horizon as an example we show how this secular growth parallels similar
phenomena for thermal systems, and how it can be resummed to allow late-time
inferences to be drawn more robustly. Some comments are made about the
appearance of an IR/UV interplay in this calculation, as well as on the
possible relevance of our calculations to predictions near black-hole horizons.Comment: LaTeX, 17 pages plus appendix; added references and subsection on
back-reactio
A 3.55 keV Photon Line and its Morphology from a 3.55 keV ALP Line
Galaxy clusters can efficiently convert axion-like particles (ALPs) to
photons. We propose that the recently claimed detection of a 3.55--3.57 keV
line in the stacked spectra of a large number of galaxy clusters and the
Andromeda galaxy may originate from the decay of either a scalar or fermionic
keV dark matter species into an axion-like particle (ALP) of mass , which subsequently converts to a photon in
the cluster magnetic field. In contrast to models in which the photon line
arises directly from dark matter decay or annihilation, this can explain the
anomalous line strength in the Perseus cluster. As axion-photon conversion
scales as and cool core clusters have high central magnetic fields, this
model can also explains the observed peaking of the line emission in the cool
cores of the Perseus, Ophiuchus and Centaurus clusters, as opposed to the much
larger dark matter halos. We describe distinctive predictions of this scenario
for future observations.Comment: 6 page
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