What is it about?

The paper deals with a quadratic f(R) theory à la Palatini, assuming that metric and connection are independent. This has a dramatic effect on the field equations, which are now different from the "more popular" case where the connection is just Levi-Civita of the metric. As a result, the internal dynamics of stars is more sensitive the density gradients, and this has an impact on nuclear reactions at the core.

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Why is it important?

Our results are important because they show that modified gravity effects can manifest themselves in low mass stars (brown dwarfs), not just on very compact neutron stars. This opens a new avenue to detect such effects in a class of objects that are receiving a lot of observational attention due to their proximity in size to giant exoplanets. If the predictions of general relativity for the lowest mass brown dwarfs are not observationally verified, that could be a sign of modified gravity.

Perspectives

There is still a lot of work to do on the theoretical side to set a general framework in which to parametrize the predictions of different theories regarding the minimum mass for hydrogen burning. Observationally there is much room for better statistics on these relatively small objects.

Gonzalo J Olmo
Universitat de Valencia

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This page is a summary of: Minimum main sequence mass in quadratic Palatini f(R) gravity, August 2019, American Physical Society (APS), DOI: 10.1103/physrevd.100.044020.
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