Search for Dark Energy with Tabletop Experiments

The existence of dark energy is one of the greatest puzzles in modern physics. The observed current accelerated expansion of the Universe provides clear evidence that there must be some unknown substance filling the Universe which can account for this observed acceleration. Cosmological observations reveal that currently about 70% of the energy content in the Universe must be due to this unknown substance, which is called dark energy. The nature of dark energy is unknown as of yet. The theoretical framework describing the Universe on cosmological scales is General Relativity. Since cosmological observations rely on General Relativity for the interpretation of the experimental results it appears natural that General Relativity might need to be modified to account for the current accelerated expansion of the Universe. While a modification for short distances is indeed easily possible, the modification of the theory for large distance scales is very intricate and would violate some of the theorys fundamental assumptions. It appears more natural to consider the existence of additional new hypothetical scalar fields, which couple to gravity and can account for dark energy. The postulation of new scalars is well motivated by new theories in the domain of particle physics. With the recent discovery of the Higgs boson a scalar particle has been actually observed, which provides further evidence of the possible existence of additional scalar fields. While the postulation of additional scalar fields appears as a natural solution to account for the unknown substance responsible for the acceleration of the Universe, those new scalars would also lead to new interactions, fifth forces. Measurements with high precision at solar as well as terrestrial scales were so far unable to detect any fifth forces. For this reason, new mechanisms have been devised, which hide those scalar fields in environments where they would lead to deviations of measurements. Those environments are typically related to high mass densities. Nevertheless, at cosmological scales where on the average the mass density is low, those fields could prevail and drive the accelerated expansion of the Universe. Interestingly, many high precision table top experiments are in principle able to detect such hypothetical new scalar fields. Recently, large efforts have been made from experimental groups as well as theorists to find any of those new scalars. Among those high precision experiments are three performed by members of the Neutron and Quantum Physics group of the Atominstitut/TU Wien. This project addresses the theoretical analysis relevant for the detection of several prominent hypothetical scalar fields, and as such the possible detection of dark energy, with these three experiments. The analysis will also include data from Lunar Laser Ranging to provide complementary access to the astrophysical regime.

The existence of dark energy (DE) is one of the greatest puzzles in modern physics. The observed current accelerated expansion of the Universe provides clear evidence that there must be some unknown substance filling the Universe which can account for this observed acceleration. Cosmological observations reveal that currently about 70% of the energy content in the Universe must be due to this unknown substance, which is DE. The nature of DE is unknown as of yet. The theoretical framework describing the Universe on cosmological scales is General Relativity. Since cosmological observations rely on General Relativity for the interpretation of the experimental results it appears natural that General Relativity might need to be modified to account for the current accelerated expansion of the Universe. While a modification for short distances is indeed easily possible, the modification of the theory for large distance scales is very intricate and would violate some of the theory's fundamental assumptions. It appears more natural to consider the existence of additional new hypothetical scalar fields, which couple to gravity and can account for DE. The postulation of new scalars is well motivated by new theories in the domain of particle physics. While the postulation of additional scalar fields appears as a natural solution to account for the unknown substance responsible for the acceleration of the Universe, those new scalars would also lead to new interactions, fifth forces. Measurements with high precision at solar as well as terrestrial scales were so far unable to detect any fifth forces. For this reason, new mechanisms have been devised, which hide those scalar fields in environments where they would lead to deviations of measurements. Those environments are typically related to high mass densities. Nevertheless, at cosmological scales where on the average the mass density is low, those fields could prevail and drive the accelerated expansion of the Universe. Interestingly, many high precision table top experiments are in principle able to detect such hypothetical new scalar fields. Recently, large efforts have been made from experimental groups as well as theorists to find any of those new scalars. Among those high precision experiments are three performed by members of the Neutron and Quantum Physics group of the Atominstitut/TU Wien. This project addressed the theoretical analysis relevant for the detection of several prominent hypothetical scalar fields, and as such the possible detection of DE, with these three experiments. The analysis included also data from Lunar Laser Ranging to provide complementary access to the astrophysical regime. The obtained results allowed to constrain unknown model parameters of diverse DE models significantly.