# Differences

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joint [2019/12/04 16:24] marta [Seminar calendar] |
joint [2019/12/04 16:27] (current) marta [Seminar calendar] |
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== 28th November 2019: Selected topics in theory and observations of Dark Energy (Tunch) == | == 28th November 2019: Selected topics in theory and observations of Dark Energy (Tunch) == | ||

- | Josue Motoa - TBA | + | Josue Motoa Manzano (Universidad de Valle, Cali, Colombia; visitor at ITP, Universität Heidelberg) - "De Sitter symmetries and inflationary correlators in parity violating scalar-vector models" |

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+ | We use conformal symmetry to constrain the shape of inflationary correlators in the presence of long-lived vector field perturbations. Applying conformal Ward identities, we derive general expressions, up to amplitudes and normalization factors, for the two and three-point correlators in the presence of vector fields mediated by the interaction f(\phi)\left(F_{\mu \nu}F^{\mu \nu}+\alpha\tilde{F}_{\mu \nu}F^{\mu \nu}\right), where f(\phi) is a suitable coupling function between the scalar and the vector field. This interaction allows for isotropy and parity symmetry breaking and is consistent with super horizon conformal symmetry. | ||

== 21st November 2019: Journal Club == | == 21st November 2019: Journal Club == | ||

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== 14th November 2019: Selected topics in theory and observations of Dark Energy (Tunch) == | == 14th November 2019: Selected topics in theory and observations of Dark Energy (Tunch) == | ||

- | Leonardo Giani - TBA | + | Leonardo Giani (UFES, Brazil; visitor at ITP, Universität Heidelberg) - "Late-times asymptotic equation of state for a class of nonlocal theories of gravity" |

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+ | We investigate the behavior of the asymptotic late-times effective equation of state for a class of nonlocal theories of gravity. These theories modify the Einstein-Hilbert Lagrangian introducing terms containing negative powers of the d'Alembert operator acting on the Ricci scalar. We find that imposing vanishing initial conditions for the nonlocal content during the radiation-dominated epoch implies the same asymptotic late-times behavior for most of these models. In terms of the effective equation of state of the universe, we find that asymptotically ωeff→−1, approaching the value given by a cosmological constant. On the other hand, unlike in the case of ΛCDM, the Hubble factor is a monotonic growing function that diverges asymptotically. We argue that this behavior is not a coincidence and discuss under which conditions this is to be expected in these nonlocal models. | ||

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+ | Based on [[ https://arxiv.org/abs/1906.10480 | view arXiv ]] | ||

== 7th November 2019: Journal Club == | == 7th November 2019: Journal Club == |