99 research outputs found
Inflating in a Better Racetrack
We present a new version of our racetrack inflation scenario which, unlike
our original proposal, is based on an explicit compactification of type IIB
string theory: the Calabi-Yau manifold P^4_[1,1,1,6,9]. The axion-dilaton and
all complex structure moduli are stabilized by fluxes. The remaining 2 Kahler
moduli are stabilized by a nonperturbative superpotential, which has been
explicitly computed. For this model we identify situations for which a linear
combination of the axionic parts of the two Kahler moduli acts as an inflaton.
As in our previous scenario, inflation begins at a saddle point of the scalar
potential and proceeds as an eternal topological inflation. For a certain range
of inflationary parameters, we obtain the COBE-normalized spectrum of metric
perturbations and an inflationary scale of M = 3 x 10^{14} GeV. We discuss
possible changes of parameters of our model and argue that anthropic
considerations favor those parameters that lead to a nearly flat spectrum of
inflationary perturbations, which in our case is characterized by the spectral
index n_s = 0.95.Comment: 20 pages, 7 figures. Brief discussion on the non-gaussianity of this
model, one more figure of the field trajectories added as well as other minor
changes to the tex
Warped Tachyonic Inflation in Type IIB Flux Compactifications and the Open-String Completeness Conjecture
We consider a cosmological scenario within the KKLT framework for moduli
stabilization in string theory. The universal open string tachyon of decaying
non-BPS D-brane configurations is proposed to drive eternal topological
inflation. Flux-induced `warping' can provide the small slow-roll parameters
needed for successful inflation. Constraints on the parameter space leading to
sufficient number of e-folds, exit from inflation, density perturbations and
stabilization of the Kahler modulus are investigated. The conditions are
difficult to satisfy in Klebanov-Strassler throats but can be satisfied in T^3
fibrations and other generic Calabi-Yau manifolds. This requires large volume
and magnetic fluxes on the D-brane. The end of inflation may or may not lead to
cosmic strings depending on the original non-BPS configuration. A careful
investigation of initial conditions leading to a phenomenologically viable
model for inflation is carried out. The initial conditions are chosen on the
basis of Sen's open string completeness conjecture. We find time symmetrical
bounce solutions without initial singularities for k=1 FRW models which are
correlated with an inflationary period. Singular big-bang/big-crunch solutions
also exist but do not lead to inflation. There is an intriguing correlation
between having an inflationary universe in 4 dimensions and 6 compact
dimensions or a big-crunch singularity and decompactification.Comment: 43 pages, 9 figures. v3: Typos correcte
Realistic D-Brane Models on Warped Throats: Fluxes, Hierarchies and Moduli Stabilization
We describe the construction of string theory models with semirealistic
spectrum in a sector of (anti) D3-branes located at an orbifold singularity at
the bottom of a highly warped throat geometry, which is a generalisation of the
Klebanov-Strassler deformed conifold. These models realise the Randall-Sundrum
proposal to naturally generate the Planck/electroweak hierarchy in a concrete
string theory embedding, and yielding interesting chiral open string spectra.
We describe examples with Standard Model gauge group (or left-right symmetric
extensions) and three families of SM fermions, with correct quantum numbers
including hypercharge. The dilaton and complex structure moduli of the geometry
are stabilised by the 3-form fluxes required to build the throat. We describe
diverse issues concerning the stabilisation of geometric Kahler moduli, like
blow-up modes of the orbifold singularities, via D term potentials and gauge
theory non-perturbative effects, like gaugino condensation. This local
geometry, once embedded in a full compactification, could give rise to models
with all moduli stabilised, and with the potential to lead to de Sitter vacua.
Issues of gauge unification, proton stability, supersymmetry breaking and
Yukawa couplings are also discussed.Comment: 46 pages, 13 figures (figures 3 and 13 corrected
Surveying Standard Model Flux Vacua on
We consider the SU(2)LxSU(2)R Standard Model brane embedding in an
orientifold of T6/Z2xZ2. Within defined limits, we construct all such Standard
Model brane embeddings and determine the relative number of flux vacua for each
construction. Supersymmetry preserving brane recombination in the hidden sector
enables us to identify many solutions with high flux. We discuss in detail the
phenomenology of one model which is likely to dominate the counting of vacua.
While Kahler moduli stabilization remains to be fully understood, we define the
criteria necessary for generic constructions to have fixed moduli.Comment: 30 pages, LaTeX, v2: added reference
Racetrack Inflation
We develop a model of eternal topological inflation using a racetrack
potential within the context of type IIB string theory with KKLT volume
stabilization. The inflaton field is the imaginary part of the K\"ahler
structure modulus, which is an axion-like field in the 4D effective field
theory. This model does not require moving branes, and in this sense it is
simpler than other models of string theory inflation. Contrary to
single-exponential models, the structure of the potential in this example
allows for the existence of saddle points between two degenerate local minima
for which the slow-roll conditions can be satisfied in a particular range of
parameter space. We conjecture that this type of inflation should be present in
more general realizations of the modular landscape. We also consider
`irrational' models having a dense set of minima, and discuss their possible
relevance for the cosmological constant problem.Comment: 23 pages 7 figures. The final version with minor modifications, to
appear in JHE
Low-Energy Brane-World Effective Actions and Partial Supersymmetry Breaking
As part of a programme for the general study of the low-energy implications
of supersymmetry breaking in brane-world scenarios, we study the nonlinear
realization of supersymmetry which occurs when breaking N=2 to N=1
supergravity. We consider three explicit realizations of this supersymmetry
breaking pattern, which correspond to breaking by one brane, by one antibrane
or by two (or more) parallel branes. We derive the minimal field content, the
effective action and supersymmetry transformation rules for the resulting N=1
theory perturbatively in powers of kappa = 1/M_{Planck}. We show that the way
the massive gravitino and spin-1 fields assemble into N=1 multiplets implies
the existence of direct brane-brane contact interactions at order O(kappa).
This result is contrary to the O(kappa^2) predicted by the sequestering
scenario but in agreement with recent work of Anisimov et al. Our low-energy
approach is model independent and is a first step towards determining the
low-energy implications of more realistic brane models which completely break
all supersymmetries.Comment: Latex, 29 Page
A muon-track reconstruction exploiting stochastic losses for large-scale Cherenkov detectors
IceCube is a cubic-kilometer Cherenkov telescope operating at the South Pole. The main goal of IceCube is the detection of astrophysical neutrinos and the identification of their sources. High-energy muon neutrinos are observed via the secondary muons produced in charge current interactions with nuclei in the ice. Currently, the best performing muon track directional reconstruction is based on a maximum likelihood method using the arrival time distribution of Cherenkov photons registered by the experiment\u27s photomultipliers. A known systematic shortcoming of the prevailing method is to assume a continuous energy loss along the muon track. However at energies >1 TeV the light yield from muons is dominated by stochastic showers. This paper discusses a generalized ansatz where the expected arrival time distribution is parametrized by a stochastic muon energy loss pattern. This more realistic parametrization of the loss profile leads to an improvement of the muon angular resolution of up to 20% for through-going tracks and up to a factor 2 for starting tracks over existing algorithms. Additionally, the procedure to estimate the directional reconstruction uncertainty has been improved to be more robust against numerical errors
Neutrino oscillation studies with IceCube-DeepCore
AbstractIceCube, a gigaton-scale neutrino detector located at the South Pole, was primarily designed to search for astrophysical neutrinos with energies of PeV and higher. This goal has been achieved with the detection of the highest energy neutrinos to date. At the other end of the energy spectrum, the DeepCore extension lowers the energy threshold of the detector to approximately 10 GeV and opens the door for oscillation studies using atmospheric neutrinos. An analysis of the disappearance of these neutrinos has been completed, with the results produced being complementary with dedicated oscillation experiments. Following a review of the detector principle and performance, the method used to make these calculations, as well as the results, is detailed. Finally, the future prospects of IceCube-DeepCore and the next generation of neutrino experiments at the South Pole (IceCube-Gen2, specifically the PINGU sub-detector) are briefly discussed
Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A
Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of e290 tera-electron volts. Its arrival direction was consistent with the location of a known g-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to g-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy g-rays. This observation of a neutrino in spatial coincidence with a g-ray-emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos
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