Oliver Janssen
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View article: The Axidental Universe
The Axidental Universe Open
Random axion theories with several hundred fields have enormous numbers of distinct meta-stable minima. A small fraction of these have vacuum energy compatible with current measurements of dark energy. The potential also contains regions s…
View article: Axion minima in string theory
Axion minima in string theory Open
A bstract We study the landscape of axion theories in compactifications of type IIB string theory on orientifolds of Calabi-Yau threefolds. In a sample of approximately 400,000 geometries we find that in the regime of perturbative control …
View article: Kontsevich-Segal criterion in the no-boundary state constrains anisotropy
Kontsevich-Segal criterion in the no-boundary state constrains anisotropy Open
We show that the Kontsevich-Segal-Witten (KSW) criterion applied to the no-boundary state constrains anisotropic deformations of de Sitter space. We consider squashed S3 and S1×S2 boundaries and find that, in both models, the KSW criterion…
View article: KSW criterion in large field models
KSW criterion in large field models Open
We extend the analytic description of complex no-boundary solutions in the context of inflation to large field models. We discuss the Kontsevich–Segal–Witten (KSW) criterion and find it is satisfied in small field models, while in large fi…
View article: The Kontsevich-Segal Criterion in the No-Boundary State Constrains Anisotropy
The Kontsevich-Segal Criterion in the No-Boundary State Constrains Anisotropy Open
We show that the Kontsevich-Segal-Witten (KSW) criterion applied to the no-boundary state constrains anisotropic deformations of de Sitter space. We consider squashed $S^3$ and $S^1 \times S^2$ boundaries and find that in both models, the …
View article: Non-analyticity of the S-matrix with spontaneously broken Lorentz invariance
Non-analyticity of the S-matrix with spontaneously broken Lorentz invariance Open
A bstract We study the S -matrix of Goldstones in the renormalizable theory of a U(1) complex scalar at finite charge, i.e. in a state that breaks Lorentz invariance. The theory is weakly coupled so that this S -matrix exists at all energi…
View article: KSW criterion in large field models
KSW criterion in large field models Open
We extend the analytic description of complex no-boundary solutions in the context of inflation to large field models. We discuss the Kontsevich-Segal-Witten (KSW) criterion and find it is satisfied in small field models, while in large fi…
View article: Positivity bounds on electromagnetic properties of media
Positivity bounds on electromagnetic properties of media Open
We study the constraints imposed on the electromagnetic response of general media by microcausality (commutators of local fields vanish outside the light cone) and positivity of the imaginary parts (the medium can only absorb energy from t…
View article: Non-analyticity of the $S$-matrix with spontaneously broken Lorentz invariance
Non-analyticity of the $S$-matrix with spontaneously broken Lorentz invariance Open
We study the $S$-matrix of Goldstones in the renormalizable theory of a $U(1)$ complex scalar at finite charge, i.e. in a state that breaks Lorentz invariance. The theory is weakly coupled so that this $S$-matrix exists at all energies. Un…
View article: Kontsevich-Segal Criterion in the No-Boundary State Constrains Inflation
Kontsevich-Segal Criterion in the No-Boundary State Constrains Inflation Open
We show that the Kontsevich-Segal (KS) criterion, applied to the complex saddles that specify the semiclassical no-boundary wave function, acts as a selection mechanism on inflationary scalar field potentials. Completing the observable pha…
View article: Axion minima in string theory
Axion minima in string theory Open
We study the landscape of axion theories in compactifications of type IIB string theory on orientifolds of Calabi-Yau threefolds. In a sample of approximately 400,000 geometries we find that in the regime of perturbative control there are …
View article: The Kontsevich-Segal Criterion in the No-Boundary State Constrains Inflation
The Kontsevich-Segal Criterion in the No-Boundary State Constrains Inflation Open
We show that the Kontsevich-Segal (KS) criterion, applied to the complex saddles that specify the semiclassical no-boundary wave function, acts as a selection mechanism on inflationary scalar field potentials. Completing the observable pha…
View article: Positivity bounds on effective field theories with spontaneously broken Lorentz invariance
Positivity bounds on effective field theories with spontaneously broken Lorentz invariance Open
We derive positivity bounds on EFT coefficients in theories where boosts are spontaneously broken. We employ the analytic properties of the retarded Green's function of conserved currents (or of the stress-energy tensor) and assume the the…
View article: Decoherence: A Numerical Study
Decoherence: A Numerical Study Open
We study quantum decoherence numerically in a system consisting of a relativistic quantum field theory coupled to a measuring device that is itself coupled to an environment. The measuring device and environment are treated as quantum, non…
View article: Axion landscape cosmology
Axion landscape cosmology Open
We study the cosmology of complex multi-axion theories. With O(100) fields\nand GUT scale energies these theories contain a vast number of vacua,\ninflationary trajectories and a natural dark matter candidate. We demonstrate\nthat the vacu…
View article: No-boundary proposal in biaxial Bianchi IX minisuperspace
No-boundary proposal in biaxial Bianchi IX minisuperspace Open
We implement the no-boundary proposal for the wave function of the Universe in an exactly solvable Bianchi IX minisuperspace model with two scale factors. We extend our earlier work [Phys. Rev. Lett. 121, 081302 (2018)] to include the cont…
View article: Multiple-axion framework
Multiple-axion framework Open
We describe a systematic framework for periodic potentials of arbitrary dimension, such as those governing multiple axions. A novel type of alignment renders even complex theories analytically tractable. Theories with ~100 axions and rando…
View article: Damped Perturbations in the No-Boundary State
Damped Perturbations in the No-Boundary State Open
We evaluate the no-boundary path integral exactly in a Bianchi type IX minisuperspace with two scale factors. In this model the no-boundary proposal can be implemented by requiring one scale factor to be zero initially together with a judi…
View article: Real no-boundary wave function in Lorentzian quantum cosmology
Real no-boundary wave function in Lorentzian quantum cosmology Open
It is shown that the standard no-boundary wave function has a natural expression in terms of a Lorentzian path integral with its contour defined by Picard-Lefschetz theory. The wave function is real, satisfies the Wheeler-DeWitt equation a…
View article: Phase diagram of dynamical twisted-mass Wilson fermions at finite isospin chemical potential
Phase diagram of dynamical twisted-mass Wilson fermions at finite isospin chemical potential Open
We consider the phase diagram of twisted mass Wilson fermions of two-flavor\nQCD in the parameter space of the quark mass, the isospin chemical potential,\nthe twist angle and the lattice spacing. This work extends earlier studies in\nthe …
View article: On the possibility of using X-ray Compton scattering to study magnetoelectrical properties of crystals
On the possibility of using X-ray Compton scattering to study magnetoelectrical properties of crystals Open
This paper discusses the possibility of using Compton scattering – an inelastic X-ray scattering process that yields a projection of the electron momentum density – to probe magnetoelectrical properties. It is shown that an antisymmetric c…