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We propose a new approach to test possible corrections to Newtonian gravity using solar physics. The high accuracy of current solar models and new precise observations allow to constrain corrections to standard gravity at unprecedented levels. Our case study is Eddington-inspired gravity, an attractive modified theory of gravity which results in non-singular cosmology and collapse. The theory is equivalent to standard gravity in vacuum, but it sensibly differs from it within matter, for instance it affects the evolution and the equilibrium structure of the Sun, giving different core temperature profiles, deviations in the observed acoustic modes and in solar neutrino fluxes. Comparing the predictions from a modified solar model with observations, we constrain the coupling parameter of the theory, |κ g | 3 · 10 5 m 5 s −2 /kg. Our results show that the Sun can be used to efficiently constrain alternative theories of gravity.

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In this work we apply relativistic mean-field theory in neutron stars assuming that fermionic dark matter is trapped inside the star and interacts directly with neutrons by exchanging Standard Model Higgs bosons. For realistic values of the parameters of the model we compute numerically the equation of state, and we compare it to the standard one. Furthermore, the mass-to-radius relation for both equations of state (pure neutron matter as well as admixed DM-neutron star) is shown, and the highest star mass for both cases is reported.

SNO measurements strongly constrain the central temperature of the Sun, to within a precision of much less than 1%. This result can be used to probe the parameter space of supersymmetric dark matter. In this first analysis we find a lower limit for the weakly interacting massive particle (WIMP) mass of 60 GeV. Furthermore, in the event that WIMPs create a quasi-isothermal core, they will produce a peculiar distribution of the solar neutrino fluxes measured on Earth. Typically, a WIMP with a mass of 100 GeV and annihilation cross section of 10(-34) cm(3)/sec will decrease the neutrino predictions, by up to 4% for the Cl, by 3% for the heavy water, and by 1% for the Ga detectors.

We report the first constraints on the properties of weakly interacting low-mass dark matter (DM) particles using asteroseismology. The additional energy transport mechanism due to accumulated asymmetric DM particles modifies the central temperature and density of low-mass stars and suppresses the convective core expected in 1.1-1.3 M stars even for an environmental DM density as low as the expected in the solar neighborhood. An asteroseismic modeling of the stars KIC 8006161, HD 52265 and α Cen B revealed small frequency separations significantly deviated from the observations, leading to the exclusion of a region of the DM parameter space mass versus spin-dependent DM-proton scattering cross section comparable with present experimental constraints.

Context. Extreme solar activity fluctuations and the occurrence of solar grand minima and maxima episodes, such as the Maunder minimum and Medieval maximum are well-established, observed features of the solar cycle. Nevertheless, such extreme activity fluctuations and the dynamics of the solar cycle during Maunder minima-like episodes remain ill understood. Aims. We explore the origin of such extreme solar activity fluctuations and the role of dual poloidal field sources, namely the BabcockLeighton mechanism and the mean-field α effect in the dynamics of the solar cycle. We mainly concentrate on entry and recovery from grand minima episodes such as the Maunder minimum and the dynamics of the solar cycle, including the structure of solar butterfly diagrams during grand minima episodes. Methods. We use a kinematic solar dynamo model with a novel set-up in which stochastic perturbations force two different poloidal sources. We explore different regimes of operation of these poloidal sources with distinct operating thresholds to identify the importance of each. The perturbations are implemented independently in both hemispheres which allows the study of the level of hemispheric coupling and hemispheric asymmetry in the emergence of sunspots. Results. From the simulations performed we identify a few different ways in which the dynamo can enter a grand minima episode. While fluctuations in any of the α effects can trigger intermittency, in keeping with results from a mathematical time-delay model we find that the mean-field α effect is crucial for the recovery of the solar cycle from a grand minima episode, which a Babcock-Leighton source alone fails to achieve. Our simulations also demonstrate many types of hemispheric asymmetries, including grand minima and failed grand minima where only one hemisphere enters a quiescent state. Conclusions. We conclude that stochastic fluctuations in two interacting poloidal field sources working with distinct operating thresholds is a viable candidate for triggering episodes of extreme solar activity and that the mean-field α effect capable of working on weak, sub-equipartition fields is critical to the recovery of the solar cycle following an extended solar minimum. Based on our results, we also postulate that solar activity can exhibit significant parity shifts and hemispheric asymmetry, including phases when only one hemisphere is completely quiescent while the other remains active, to, successful grand minima like conditions in both hemispheres.

Solar neutrinos coming from different nuclear reactions are now detected with a high statistics. Consequently, an accurate spectroscopic analysis of the neutrino fluxes arriving on the Earth's detectors become available, in the context of neutrino oscillations. In this work, we explore the possibility of using this information to infer the radial profile of the electronic density in the solar core. So, we discuss the constraints on the Sun's density and chemical composition that can be determined from solar neutrino observations. This approach constitutes an independent and alternative diagnostic to the helioseismic investigations already done. The direct inversion method, that we propose to get the radial solar electronic density profile, is almost independent of the solar model.