<p>In this talk I will focus on some modifications of General Relativity, particularly on the so-called f(R) gravities within the Palatini formalism. I will introduce a reformulation of the variational principle for this class of theories that allows us to obtain the analog of the Gibbons-Hawking-York term that should be subtracted in the action to establish a well-posed variational principle. Among many applications, this leads to the correct expression for the Black Hole entropy for Schwarzschild spacetimes through the Euclidean semiclassical approach. I will also present the so-called 3+1 decomposition within these theories and the derivation of the corresponding Israel junction conditions.

</p><p><br></p><p><b>Unirse desde el enlace de la reunión:

</b></p><p><a href="https://universidaddevalladolid.webex.com/universidaddevalladolid/j.php?MTID=mcc1e57bb72f852f1ef84b2d079a89253">https://universidaddevalladolid.webex.com/universidaddevalladolid/j.php?MTID=mcc1e57bb72f852f1ef84b2d079a89253</a>
</p><p><br></p><p><b>Unirse mediante el número de la reunión:

</b></p><p>Número de reunión (código de acceso): 121 350 3266

</p><p>Contraseña de la reunión: iQNmpk922DX
</p>