arXiv subjects

Jan-Markus Schwindt

Publications and source records attributed to Jan-Markus Schwindt.

11 recordsLinked to original sources

arXiv2018

Neutrino flavor-mass uncertainty relations and an entanglement-assisted determination of the PMNS matrix

As a result of a non-trivial mixing matrix, neutrinos cannot be simultaneously in a flavor and mass eigenstate. We formulate and discuss information entropic relations that quantify the associated quantum uncertainty. We also formulate a protocol to determine the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix from quantum manipulations and measurements on an entangled lepton-neutrino pair. The entangled state features neutrino oscillations in a conditional probability involving measurements on the lepton and the neutrino. They can be switched off by choosing a specific observable on the lepton side which is determined by the PMNS matrix. The parameters of the latter, including the CP-violating phase $δ$, can be obtained by guessing them and improving the guess by minimizing the remaining oscillations.

hep-ph↗

arXiv2012

Nothing happens in the Universe of the Everett Interpretation

Since the scalar product is the only internal structure of a Hilbert space, all vectors of norm 1 are equivalent, in the sense that they form a perfect sphere in the Hilbert space, on which every vector looks the same. The state vector of the universe contains no information that distinguishes it from other state vectors of the same Hilbert space. If the state vector is considered as the only fundamental entity, the world is completely structureless. The illusion of interacting subsystems is due to a "bad" choice of factorization (i.e. decomposition into subsystems) of the Hilbert space. There is always a more appropriate factorization available in which subsystems don't interact and nothing happens at all. This factorization absorbs the time evolution of the state vector in a trivial way. The Many Worlds Interpretation is therefore rather a No World Interpretation. A state vector gets the property of "representing a structure" only with respect to an external observer who measures the state according to a specific factorization and basis.

quant-ph↗

arXiv2008

Asymptotically free four-fermion interactions and electroweak symmetry breaking

We investigate the fermions of the standard model without a Higgs scalar. Instead, we consider a non-local four-quark interaction in the tensor channel which is characterized by a single dimensionless coupling $f$. Quantization leads to a consistent perturbative expansion for small $f$. The running of $f$ is asymptotically free and therefore induces a non-perturbative scale $Λ_{ch}$, in analogy to the strong interactions. We argue that spontaneous electroweak symmetry breaking is triggered at a scale where $f$ grows large and find the top quark mass of the order of $Λ_{ch}$. We also present a first estimate of the effective Yukawa coupling of a composite Higgs scalar to the top quark, as well as the associated mass ratio between the top quark and the W boson.

hep-ph↗

arXiv2007

Chiral tensor fields and spontaneous breaking of Lorentz symmetry

Antisymmetric tensor fields interacting with quarks and leptons have been proposed as a possible solution to the gauge hierarchy problem. We compute the one-loop beta function for a quartic self-interaction of the chiral antisymmetric tensor fields. Fluctuations of the top quark drive the corresponding running coupling to a negative value as the renormalization scale is lowered. This may indicate a non-vanishing expectation value of the tensor field, and thus a spontaneous breaking of Lorentz invariance. Settling this issue will need the inclusion of tensor loops.

hep-ph↗

arXiv2006

Scale-dependent metric and causal structures in Quantum Einstein Gravity

Within the asymptotic safety scenario for gravity various conceptual issues related to the scale dependence of the metric are analyzed. The running effective field equations implied by the effective average action of Quantum Einstein Gravity (QEG) and the resulting families of resolution dependent metrics are discussed. The status of scale dependent vs. scale independent diffeomorphisms is clarified, and the difference between isometries implemented by scale dependent and independent Killing vectors is explained. A concept of scale dependent causality is proposed and illustrated by various simple examples. The possibility of assigning an "intrinsic length" to objects in a QEG spacetime is also discussed.

hep-th↗

arXiv2006

Scale Dependent Metric and Minimal Length in QEG

The possibility of a minimal physical length in quantum gravity is discussed within the asymptotic safety approach. Using a specific mathematical model for length measurements ("COM microscope") it is shown that the spacetimes of Quantum Einstein Gravity (QEG) based upon a special class of renormalization group trajectories are "fuzzy" in the sense that there is a minimal coordinate separation below which two points cannot be resolved.

hep-th↗

arXiv2005

A Minimal Length from the Cutoff Modes in Asymptotically Safe Quantum Gravity

Within asymptotically safe Quantum Einstein Gravity (QEG), the quantum 4-sphere is discussed as a specific example of a fractal spacetime manifold. The relation between the infrared cutoff built into the effective average action and the corresponding coarse graining scale is investigated. Analyzing the properties of the pertinent cutoff modes, the possibility that QEG generates a minimal length scale dynamically is explored. While there exists no minimal proper length, the QEG sphere appears to be "fuzzy" in the sense that there is a minimal angular separation below which two points cannot be resolved by the cutoff modes.

hep-th↗

arXiv2005

The cosmological constant problem in codimension-two brane models

We discuss the possibility of a dynamical solution to the cosmological constant problem in the contaxt of six-dimensional Einstein-Maxwell theory. A definite answer requires an understanding of the full bulk cosmology in the early universe, in which the bulk has time-dependent size and shape. We comment on the special properties of codimension two as compared to higher codimensions.

hep-th↗

arXiv2005

Dark energy cosmologies for codimension-two branes

A six-dimensional universe with two branes in the "football-shaped" geometry leads to an almost realistic cosmology. We describe a family of exact solutions with time dependent characteristic size of internal space. After a short inflationary period the late cosmology is either of quintessence type or turns to a radiation dominated Friedmann universe where the cosmological constant appears as a free integration constant of the solution. The radiation dominated universe with relativistic fermions is analyzed in detail, including its dimensional reduction.

hep-th↗

arXiv2003

Holographic Branes

We discuss the properties of codimension-two branes and compare them to codimension-one branes. In particular, we show that for deficit angle branes the brane energy momentum tensor is uniquely related to integration constants in the bulk solution. We investigate chiral fermions whose wave functions are concentrated on the brane, while all their properties in the effective four-dimensional world can be inferred from the tail of the wave function in the bulk, thereby realizing a holographic principle. We propose holographic branes for which the knowledge of the bulk geometry is sufficient for the computation of all relevant properties of the observable particles, independently of the often unknown detailed physics of the branes.

hep-th↗

arXiv2001

Structure Formation and the Time Dependence of Quintessence

We discuss the influence of dark energy on structure formation, especially the effects on σ_8. Our interest is particularly focused on quintessence models with time-dependent equation of state and non-negligible quintessence component in the early universe. We obtain an analytic expression for σ_8 valid for a large class of dark energy models. We conclude that structure formation is a good indicator for the history of dark energy and use our results to set constraints on quintessence models.

astro-ph↗