Dark Matter & Modified Gravity
Project members: Michael Krämer, Dennis Lehmkuhl, Erhard Scholz
Astrophysical observations and explanatory gaps in the Standard Model of particle physics imply the existence of Dark Matter and/or a modification of our theory of space and time. A decision between the Dark Matter and Modified Gravity approaches is hampered by problems of underdetermination at different levels and of different kinds. In order to specify these problems, we shall analyse in detail the landscape of Dark Matter and Modified Gravity models, and the interplay between research in particle physics, astrophysics, and gravity. The plethora of Dark Matter and Modified Gravity approaches, and the corresponding underdetermination, even in the light of the vast amount of relevant collider based and astrophysical observations, clearly illustrates the complexity of this scientific problem. On the other hand, the overlap of the collider and astrophysical domains may allow for reducing the underdetermination, thus leading to a simplification of the model landscape. Our focus is on Dark Matter searches at the Large Hadron Collider and the connection between LHC results and theories of gravity. We will address the question of different kinds of underdetermination, both in choosing between the two research programs of Dark Matter and Modified Gravity, and also in choosing between different models within each program. In particular, we shall provide an assessment of the explanatory power and the explanatory gaps of the Dark Matter and Modified Gravity hypotheses, and study the coarse-graining of the model landscape introduced by so-called simplified models, which may allow us to distinguish different kinds of aiming for simplicity in high-energy physics.
Comparativism (about mass)
This project forms part of the bigger project of determining which metaphysical conclusions we can draw from physical theories, or more specifically from the symmetries of those physical theories. As an initial case study I am investigating the case of mass in Newtonian Gravity: would a uniform doubling of all the masses of all the particles generate a detectable difference? If so, we need absolute intrinsic masses in our ontology. If not, we can be a comparativist about mass: mass relations are sufficient. I intend to formulate a general framework based on this case study, and apply this framework to further examples such as electric charge, handedness and length.
A pop-science introduction to my Dphil (= phd) project can be viewed here or below:
“Regularity Comparativism about Mass in Newtonian Gravity”, forthcoming in Philosophy of Science 84(5) (copy available upon request)
Related works in progress:
“Against Reducing Newtonian Mass to Kinematical Quantities” (under review)
“Detecting Absolute Newtonian Masses”
“On the empirical inadequacy of comparativism about mass in Newtonian Gravity”, with Oliver Pooley
“Machian Comparativism about Mass in Newtonian Gravity”
The Metaphysics of Emergent Spacetime Theories
The debate about the ontology of spacetime is standardly construed as a dilemma between substantivalism and relationalism. I argue that a trilemma is more appropriate, emergent spacetime theories being the third category. Philosophical arguments do not distinguish between emergent spacetime and its effective substantival counterpart. It is arguments from physics that force us to give up substantivalism in favour of emergent spacetime theories. The remaining new dilemma is between emergent spacetime and relationalism. I provide a list of questions which one should consider when discussing emergent spacetime theories and apply them to a quantum super fluid toy model of emergent spacetime.
This paper is under review; a copy is available upon request.
Galactic Sources of Ultrahigh-Energy Cosmic Rays
Upper Limit for the Deuteron Electric Dipole Moment
There is an enormous unexplained asymmetry between the quantities of matter and anti-matter in our universe. One of the three necessary Sakharov conditions for such an asymmetry to occur is the existence of processes that violate CP-symmetry: the process involving matter must occur at different rates from the mirrored process involving its anti-matter counterpart. We have calculated the corrections to the energy levels of deuterium if the deuteron were to have a (CP-violating) electric dipole moment, using second-order perturbation theory in non-relativistic quantum mechanics. Equating these corrections to the maximum allowed by the approximate agreement between the theoretical energy levels and experimental spectroscopic values gives an upper limit for the deuteron electric dipole moment of 8.8 * 10^-16 e*cm, as reported here.