Sjoerd Hardeman

joerd Hardeman

PhD student theoretical cosmology and high energy physics

Leiden Institute of Physics
Leiden University
Niels Bohrweg 2
NL-2333 CA Leiden
The Netherlands
Phone: +31-71-5275526
Fax: +31-71-5275511
GPG key (ID: F63938E5)


I am doing research on heavy physics modifications of the standard inflationary picture. Such modification might lead to features that can be tested with experiments. Heavy physics modifications are expected as UV-complete theories like string theory require many additional degrees of freedom, which are then stabilised by some means so that the low energy physics is unaltered. These stabilisation mechanisms work only partially, usually the extra degrees of freedom cannot be consistently integrated out. This leads to alterations of low energy physics, were inflation is probably the most sensitive probe to such effects. My goal is to find these effects and classify its impact on cosmological observables, like the perturbation power spectrum and nongaussianities as can be measured from the Cosmic Microwave Background. Using this, I hope to be able to make progress on the reverse problem, that is measuring very precisely these observables and use this to reconstruct the inflationary potential. This can then be used as a tool to provide useful information on string theory and its vacuum structure.

Another very interesting question is the behaviour of matter under extreme conditions. It might be that in neutron stars, the remnants of the cores heavy stars that exploded in a supernova, contain free quarks. This can happen as the Fermi energy can be higher than the confinement threshold, making a description in quark degrees of freedom the valid description. This leads to alterations in the mass-radius relation, cooling rates, magnetic field behaviour and acoustic behaviour that can in principle be tested against observations of these compact stars.


My thesis

On Inspire
On Spires: find ea Hardeman,Sjoerd
On arXiv:

Sjoerd Hardeman, Johannes M. Oberreuter, Gonzalo A. Palma, Koenraad Schalm and Ted van der Aalst, The everpresent eta-problem: knowledge of all hidden sectors required, Accepted for publication in JHEP, arXiv:1012.5966
Ana Achucarro, Jinn-Ouk Gong, Sjoerd Hardeman, Gonzalo A. Palma and Subodh P. Patil, Features of heavy physics in the CMB power spectrum, JCAP01:030 (2011), arXiv:1010.3693
Ana Achucarro, Jinn-Ouk Gong, Sjoerd Hardeman, Gonzalo A. Palma and Subodh P. Patil, Mass hierarchies and non-decoupling in multi-scalar field dynamics, arXiv:1005.3848
Sjoerd Hardeman, Quark matter influence on observational properties of compact stars, Nucl. Phys. A820:211C-214C (2009), arXiv:0810.2306
A. AchĂșcarro, S. Hardeman and K. Sousa, F-term uplifting and the supersymmetric integration of heavy moduli, JHEP11:003 (2008), arXiv:0809.1441
A. AchĂșcarro, S. Hardeman and K. Sousa, Consistent Decoupling of Heavy Scalars and Moduli in N=1 Supergravity, Phys. Rev. D78 101901(R) (2008), arXiv:0806.4364


Assignments and reports written for my study. Note that quite a few are in Dutch.