Ruprecht Karls Universität Heidelberg

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joint [2019/05/15 14:43]
manuel [Seminar calendar]
joint [2019/12/04 16:27] (current)
marta [Seminar calendar]
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 ===Thursday,​ PW 12, Room 106=== ===Thursday,​ PW 12, Room 106===
-== 13:00 - 15:00 ==+== 13:15 - 15:00 ==
  
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-Go to the calendar of [[seminar|Cosmology seminars]] **(Usually on Tuesday, ​11am, Phil 16)**+Go to the calendar of [[seminar|Cosmology seminars]] **(Usually on Tuesday, ​2:45pm, Phil 19)**
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 ====Seminar calendar==== ====Seminar calendar====
 +
 +__**Winter term 19/20:**__
 +
 +== 20th February 2020: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +TBA
 +
 +== 13th February 2020: Journal Club ==
 +
 +TBA
 +
 +== 6th February 2020: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +TBA
 +
 +== 30th January 2020: Journal Club ==
 +
 +TBA
 +
 +== 23rd January 2020: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +TBA
 +
 +== 16th January 2020: Journal Club ==
 +
 +TBA
 +
 +== 9th January 2020: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +TBA
 +
 +== 2nd January 2020: Journal Club ==
 +
 +Christmas break 
 +
 +== 26th December 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +Christmas break 
 +
 +== 19th December 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +TBA
 +
 +== 12th December 2019: Journal Club ==
 +
 +TBA
 +
 +== 5th December 2019: Journal Club ==
 +
 +Cancelled due to overlap with the Cosmology Seminar.
 +
 +
 +== 28th November 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +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"​
 +
 +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 ==
 +
 +Manuel Wittner \\
 +
 +Trans-Planckian Censorship and Inflationary Cosmology \\
 +Alek Bedroya, Robert Brandenberger,​ Marilena Loverde, Cumrun Vafa \\
 +[[ https://​arxiv.org/​abs/​1909.11106 | view arXiv ]]
 +
 +
 +== 14th November 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +Leonardo Giani (UFES, Brazil; visitor at ITP, Universität Heidelberg) - "​Late-times asymptotic equation of state for a class of nonlocal theories of gravity"​
 +
 +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.
 +
 +Based on [[ https://​arxiv.org/​abs/​1906.10480 | view arXiv ]]
 +
 +== 7th November 2019: Journal Club ==
 +
 +Ana Marta Pinho \\
 +
 +Planck evidence for a closed Universe and a possible crisis for cosmology \\
 +Eleonora Di Valentino, Alessandro Melchiorri and Joseph Silk \\
 +
 +[[ https://​www.nature.com/​articles/​s41550-019-0906-9?​fbclid=IwAR04HICL_HFWtoAIDdynFGcaBUJXGI_DL9Tc_bjA94dHrE9f9p7gsFTTmME | link to the article ]]
 +
 +== 31st October 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +Manuel Wittner (ITP, Universität Heidelberg) - "​Challenges of Stringy Quintessence:​ the F-term Problem"​
 +
 +In light of the recently proposed de Sitter-swampland conjecture, string theory seems to favor dynamic dark energy models like quintessence over a cosmological constant to drive the late time acceleration of the universe. In this talk I argue, however, that stringy quintessence models are difficult to realize as well. I elaborate on the light volume problem and identify a so called "​F-term problem":​ The positive energy density of standard-model SUSY breaking is higher than the depth of all known negative contributions. Resolving this issue would require new, unknown contributions to the vacuum energy and therefore necessitates further analysis. \\
 +(Based on the recent paper [[ http://​arxiv.org/​abs/​1909.08625 | view arXiv ]])
 +
 +== 24th October 2019: Journal Club ==
 +
 +Arvid Weyrauch \\
 +
 +Obtaining Precision Constraints on Modified Gravity with Helioseismology \\
 +Ippocratis Saltas, Ilídio Lopes \\
 +[[ https://​arxiv.org/​abs/​1909.02552 | view arXiv ]]
 +
  
 __**Summer term 19:**__ __**Summer term 19:**__
 +
 +
 +== 25th July 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +Giorgio Laverda (ITP, Universität Heidelberg) - "The entropic theory of gravity"​
 +
 +Since its first appearance in 2010, the theory of entropic gravity has been widely debated. The interpretation of gravity as an entropic force appears to be capable of describing Newtonian gravity and general relativity. In this talk I will introduce the basic principles of the theory while highlighting the controversial points.
 +
 +== 18th July 2019: Journal Club ==
 +
 +Canceled due to overlap with cosmology seminar.
 +
 +== 11th July 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +Jakob Henrichs (ITP, Universität Heidelberg) - "Milky Way rotation curve in modified gravity"​
 +
 +Rotation curves of galaxies provide a strong evidence for dark matter and can be used to test modified gravity theories. In this talk I show the results of an analysis of the Milky Way rotation curve in modified gravity. I use the Horndeski Theory to derive the gravitational potential and two different dark matter models for the analysis.
 +
 +== 4th July 2019: Journal Club ==
 +
 +Oliver Fabio Piattella \\
 +
 +Can the quantum vacuum fluctuations really solve the cosmological constant problem? \\
 +Gabriel R. Bengochea, Gabriel León, Elias Okon, Daniel Sudarsky \\
 +[[ https://​arxiv.org/​abs/​1906.05406 | view arXiv ]]
 +
 +== 25th June 2019, PW 12, Room 060 (NOTE UNUSUAL DATE AND LOCATION): Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +Adrià Gòmez-Valent (ITP, Universität Heidelberg) - "​Quantifying the evidence for the current speed-up of the Universe with low and intermediate-redshift data. A more model-independent approach"​
 +
 +According to cosmological low and intermediate-redshift
 +data, what is the statistical evidence in favor of the current
 +speed-up of the Universe? Although this question seems to be kind of
 +outdated, a quick review to the many papers that address this pivotal
 +question in the literature tells us that the answer is not obvious at
 +all. Determining the value of the deceleration parameter in the
 +context of particular cosmological models, concrete parametrizations
 +of the cosmographical quantities, or even using truncated
 +cosmographical expansions in which the truncation order is set in an
 +ad hoc way
 +can lead to biased estimations of the value of the deceleration
 +parameter at present, q0, and its uncertainty. In this talk, which is
 +based on arXiv:​1810.02278,​ JCAP 05 (2019) 026, I present a new
 +determination of q0 obtained with data from the Pantheon+MCT
 +compilation of supernovae of Type Ia, cosmic chronometers and baryon
 +acoustic oscillations. I apply the so-called Weighted Function
 +Regression method to reconstruct q(z) more model-independently than
 +many analyses in the literature, improving in this way the usual
 +cosmograhical approach. We will see, for instance, that using only the
 +first two data sets the level of evidence for the current positive
 +acceleration of the universe is only moderate (using Jeffreys'​ scale
 +and jargon), contrary to the more than 17\sigma-evidence found in the
 +framework of the standard flat LCDM model. The level of evidence grows
 +up to the very strong one when BAO data are also considered, giving
 +rise to q0= -0.60 +- 0.10, with a deceleration-acceleration transition
 +redshift at z_t = 0.80 +- 0.10. The jerk is also reconstructed,​
 +although unfortunately current data is unable to set stringent
 +constraints to this cosmographical parameter.
 +
 +== 19th June 2019, PW 12, Room 060 (NOTE UNUSUAL DATE AND LOCATION): Journal Club ==
 +
 +Giorgio Laverda \\
 +
 +Strong gravity signatures in the polarization of gravitational waves \\
 +S. Shankaranarayanan \\
 +[[https://​arxiv.org/​abs/​1905.03943 | view arXiv ]] \\
 +
 +Julius Wons
 +
 +Gravitational wave standard sirens and cosmological parameter measurement \\
 +Xin Zhang \\
 +[[https://​arxiv.org/​abs/​1905.11122 | view arXiv ]] \\
 +
 +== 13th June 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==
 +
 +Arvid Weyrauch & Manuel Wittner (ITP, Universität Heidelberg) - “Cosmology,​ philosophically speaking” (Collective Discussions) ​
 +
 +As researchers we tend to find answers using the scientific method. However, some questions may not have an answer but still spark a lot of different thoughts and perspectives. In this tunch, we will address some of these questions, from the nature of time to its beginning.
 +
 +== 6th June 2019: Journal Club ==
 +
 +Leonardo Giani \\
 +
 +Is Gravity Actually the Curvature of Spacetime? \\
 +Sebastian Bahamonde, Mir Faizal \\
 +[[https://​arxiv.org/​abs/​1905.04372 | view arXiv ]] \\
 +
 +Ana Marta Pinho \\
 +
 +Black hole shadow as a standard ruler in cosmology \\
 +Oleg Yu. Tsupko, Zuhui Fan, Gennady S. Bisnovatyi-Kogan \\
 +[[https://​arxiv.org/​abs/​1905.10509 | view arXiv ]] \\
 +
  
 == 29th May 2019, PW 12, Room 060 (NOTE UNUSUAL DATE AND LOCATION): Selected topics in theory and observations of Dark Energy (Tunch) == == 29th May 2019, PW 12, Room 060 (NOTE UNUSUAL DATE AND LOCATION): Selected topics in theory and observations of Dark Energy (Tunch) ==
  
-Oliver Piattella (UFES, Brazil; visitor at ITP, Universität Heidelberg) - TBA+Oliver Piattella (UFES, Brazil; visitor at ITP, Universität Heidelberg) - "​Neutron stars masses in R^2 gravity"​ 
 + 
 +We investigate the mass-radius (M-R) relation for 
 +neutron stars in f(R) = R + R^2 gravity. We adopt a spherically 
 +symmetric metric and a SLy equation of state. We stress how in f(R) 
 +gravity it is possible to define mass in many inequivalent ways which 
 +are nonetheless all equivalent in General Relativity. We investigate 
 +the role of the extra scalar degree of freedom in the definition of 
 +the masses and in the features of the M-R relation.
  
 == 23rd May 2019: Journal Club == == 23rd May 2019: Journal Club ==
  
-TBA+Adrià Gomez-Valent \\ 
 + 
 +Recasting H0 tension as OmegaM tension at low z \\ 
 +Eoin Ó Colgáin \\ 
 +[[https://​arxiv.org/​abs/​1903.11743 | view arXiv ]] \\ 
 + 
 +Leonardo Giani \\ 
 + 
 +How to Hide a Cosmological Constant \\ 
 +S. Carlip \\ 
 +[[https://​arxiv.org/​abs/​1905.05216 | view arXiv ]] 
  
 == 16th May 2019: Selected topics in theory and observations of Dark Energy (Tunch) == == 16th May 2019: Selected topics in theory and observations of Dark Energy (Tunch) ==

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