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Posted by: Diego Rubiera-Garcia | May 30th, 2018 |

Title: Mapping Ricci-based theories of gravity into General Relativity?

Speaker: Victor I. Afonso (Lincoln University)

Abstract: Extensions of GR are motivated by multiple reasons, and a plethora of alternative gravity models currently exist in the literature. However, confronting the predictions of those theories with observational data represents a formidable challenge. In this talk we show that for a (broad) class of gravity theories, the analysis and confrontation with observations can be carried out systematically by borrowing techniques, methods and solutions previously developed for GR. This is possible thanks to the existence of a correspondence between the spaces of solutions of those theories. We show how to obtain this correspondence in general, and illustrate the process for some matter sources with a particular gravity theory.

Title: Nonlocal Teleparallel Gravity.

Speaker: Sebastián Bahamonde (Lincoln University)

Abstract: Teleparallel gravity is a theory which assumes a zero curvature and a non-vanishing torsion. Classically, it gives the same field equations as General Relativity. However, because these theories are conceptually different, they are expected to produce different quantum effects. In this talk, I will present a non-local version of Teleparallel gravity which indeed is different than a non-local version of GR. One can generalise this model and formulate a theory which encapsulates either standard non-local theories and Teleparallel ones. Finally, I will show the most important results of our studies in the context of cosmology.

Title: Palatini stars.

Speaker: Aneta Wojnar (Curie University, Poland)

Abstract: I will briefly present the so far progress on relativistic stars in Palatini gravity. One may expect the discussion on the stability problem as well as the very first approach to some special types of stars whose stellar structure is provided by the modified gravity.

Title: The Gauss-Bonnet Extension to Teleparallel Gravity.

Speaker: Gabriel Farrugia (Malta University)

Abstract: The study of torsional based gravitational theories has been increasingly picking up interest as an alternative approach to understanding gravity. In this talk, the role of the spin connection and vielbein is discussed. Afterwards, the teleparallel analogue of the Gauss-Bonnet curvature scalar is explored in what is known as f(T, TG) gravity using reconstruction techniques in a FLRW background. Since the Lagrangian yields difficult to solve modified Friedmann equations, specific model ansatz for the f(T, TG) function are chosen and solved for a diverse number of commonly known cosmological behaviours. Lastly, the gravitational waves arising from the theory are discussed.

Title: TBA.

Speaker: Maria L. Di Tommaso (Malta University)

Abstract: TBA.

Title: Towards a Finsler-based extended theory of gravity.

Speaker: Nicoleta Voicu (Transilvania University, Brasov, Romania)

Abstract: Lorentz-Finsler geometry is a generalization of pseudo-Riemannian geome- try of spacetime, which retains various important aspects of the Riemannian spacetime model - weak equivalence principle, clock postulate, a precise notion of causal structure of spacetime as well as observers and their measurements - while allowing the metric tensor to depend on a directional variable. This will naturally lead to a modification of the description of gravity and its dynamics. Our common objectives are: O1) Investigation of the possibility of the formulation of an extended theory of gravity (ETG) on the basis of Finsler geometry. This includes: - Establishing a well-grounded model, both from a mathematical point of view and from a physical one (including field equations) - which is, despite several attempts, still missing. The geometric setting we propose is based on the ideas and tools of global variational calculus. - A detailed study of some models given by small Finslerian perturbations of classical solutions of Einstein field equations (e.g., Schwarzschild metric). O2) Obtaining a comparison of the predictions of such theories with experimental data. In particular we investigate if Finslerian spacetime geometries are capable of shedding light onto dark energy and dark matter from a geometric point of view.

Title: Covariant Galileons & Cosmology.

Speaker: Simone Peirone (Instituut-Lorenz for Theoretical Physics, Leiden)

Abstract: In my talk I will present the Covariant Galileon models as modification to gravity. I will first introduce the covariant construction of the theory as well as its formulation within the Effective Field Theory of Dark Energy. Finally, I will present the strategy we adopted in order to implement this class of models in the public Einstein-Botlzmann solver EFTCAMB, which allowed us to study the cosmology of the theory as well as to set relevant constraints on the models parameters.

Title: The de-Sitter Limit of Theories of Modified Gravity and Dark Energy.

Speaker: Georgios Papadomanolakis (Instituut-Lorenz for Theoretical Physics, Leiden)

Abstract: In this talk I will go into the de-Sitter limit of a broad class of models of MG/DE within the framework of the Effective Field Theory of Dark Energy and Modified Gravity. After introducing the framework I will focus on the stability conditions with special attention given to the tachyon instability. In order to study this I will construct a gauge-invariant quantity to describe the dark energy dof. Finally I will comment on the relation between this gauge-invariant quantity and the usual curvature perturbation.

Title: Women and Science: What the Google Memo got Wrong.

Speaker: Gina Rippon (Aston Brain Centre, Birmingham, UK)

Abstract:Statistics on the gender gaps in science make depressing reading. The UNESCO Institute of Statistics 2018 report shows that, globally, only 28.8% of science researchers are female. The UK’s 38.6% and the 32.3% for North America and Western Europe show that, even in the more developed countries women make up only just over a third of the science research workforce. Across the full range of the STEM workforce in the UK, a 2016 report found that there were just over 450,000 women; if there were gender parity the number would be 1.2 million. Explanations of these gaps encapsulate almost every aspect of wider arguments about the origin of sex/gender differences. A powerful undercurrent is that biological factors are the prime determinants of who will (and won’t) succeed in science. This meme has actually been around for centuries’ but is still overtly or covertly expressed, most recently in the contents of a memo from a Google employee, who felt that Google were wasting their time on diversity initiatives when the basic problem was that women were naturally unsuited for the demands of the job. This talk will examine the evidence behind such claims, particularly the notion of brain-based deficits. In addition, it will demonstrate how both brain and behaviour can be affected by robustly gendered and stereotyped attitudes about science and scientists, leading to self- fulfilling prophecies of under-performance and dis-engagement. The under-representation of women in science is a waste of human capital; hopefully, understanding the origins may pave the way for solutions.

Title: Scalar and vector fields consistently coupled to the energy-momentum tensor.

Speaker: J.M. Sanchez Velazquez (Universidad Complutense de Madrid, Spain)

Abstract:Within this work theories for scalar and vector fields coupled to the energy-momentum tensor are considered. We deal with the self interactions appearing in these models and we make these theories consistent. Interactions with matter are also considered using a scalar field as a proxy for the matter sector. We also discuss the ambiguity introduced by superpotential (boundary) terms in the definition of the energy-momentum tensor and use them to show that it is also possible to generate Galileon- like interactions with this procedure.

Title: Noether Symmetries as a geometric criterion to select theories of gravity.

Speaker: K. Dialektopoulos (University of Naples "Federico II", Italy)

Abstract:General relativity is plagued with some shortcomings and alternatives are being pursued at least for the last decade. I will present how we can use Noether Symmetries in order to select theories of gravity (or better to constrain abstract actions), and moreover how to use the symmetries of the theory to find exact solutions.

Title: Women in men ́s worlds. The gender gap in Physics in Spain.

Speaker: Elisa G. Mingo (Centro Universitario Villanueva, Madrid)

Abstract: Although the limited presence of women in the field commonly referred to as STEM (Science, Technology, Engineering and Mathematics) has been documented - (Grant, 2017; Hill et al., 2010) and that there have been great advances in the research of women and science in Spain (Díaz, 2008; López-Sancho, 2016, García-Calvente et al., 2015), the matter of gender gap in physics remains a research challenge. The field of Physics has a high occupational segregation in Spain, as the female presence is even lower than in other Sciences in general: women are only 21,9% of all the staff of Sciences and Physical Technologies of the Spanish State Research Agency. The available figures point out that only 10% of researchers in Theoretical Physics who have a permanent position in Europe are women and, in the field of research in Theory of Strings ("the stringuists"), the percentage is even lower (Lledó, 2017). This paper defends that there is a gender gap in the Physical Sciences, which is appreciated in: (1) the existence of a "glass ceiling" greater than in other Sciences. (2) the lack of recognition and visibility of women scientists, women have won 13,6% of the «Príncipe de Asturias» prize between 1981-2015 and 7,7% of the National Awards between 1982 and 2015 (AMIT-MINECO, 2015) as well such as the sexist stereotypes associated with the lack of scientific capacity (Bian et al; 2017); (3) the existence of under documented harassment and discriminatory experiences. Our research challenges, to be pursued reviewing secondary data and producing qualitative data women physicists, are: (a) to monitor the barriers that women have to access to the occupation; as well as the career abandonement; (b) to analyze the existence of a fractal effect in the organization (management, participation in committees ...); (d) to study the relationship between maternity, work-life balanced; (e) to study the impact of harassment and sexist discrimination experiences in job abandonement.

Title: Physics under the Gravitational Rainbow.

Speaker: Claudia de Rham (Imperial College London, UK)

Abstract: The recent direct detection of gravitational waves marks the beginning of a new era for physics and astronomy with an opportunity the probe gravity at its most fundamental level. I will discuss how the behaviour of gravity on large scales may differ from General Relativity and its implications for early and late-time cosmology as well as the potential signatures on the spectrum of gravitational waves observable at LIGO and LISA. .

Title: Neutrino masses from cosmology et al.

Speaker: Olga Mena (University of Valencia - CSIC, Valencia)

Abstract: In this talk, I will present first our current knowledge of the absolute scale of neutrino masses and their ordering from cosmology and neutrino oscillation data. I will also describe the perspectives from future cosmological probes. The implications from the strong degeneracy between the dark energy equation of state and the neutrino mass will also be discussed.

Title: New constraints on interacting vacuum dark energy

Speaker: Natalie Hogg (ICG Portsmouth, UK)

Abstract: Interacting dark energy- dark matter models have been widely studied in the literature due to their ability to resolve long-standing cosmological tensions. In my talk, I will discuss the interacting vacuum scenario and my recent work on the reconstruction of the vacuum-dark matter coupling in this scenario, focusing on the different reconstruction methods used.

Title: Constraints on metric-affine gravities using non-metricity induced effective interactions.

Speaker: Adrià Delhom (University of Valencia - CSIC, Valencia)

Abstract: Relaxing the Riemannian condition to incorporate geometric quantities such as torsion and non-metricity may allow to explore new physics associated with defects in a hypothetical space–time microstructure. Here we show that non-metricity of Ricci-Based Gravities (RBGs) produces observable effects in quantum fields in the form of contact interactions. Using Bhabha and photon-photon scatttering data, we will set constraints on the scale at which RBG deviates from GR and non-metricity becomes relevant. We obtain a bound of the order of 1TeV, which represents an improvement of several orders of magnitude to previous experimental constraints.

Title: Torsion Wave Solutions in Metric-affine Gravity

Speaker: Elvis Barakovic (University of Tuzla, Bosnia-Herzegovina)

Abstract: We construct new explicit vacuum solutions of quadratic metric-affine gravity. The approach of metric-affine gravity in using an independent affine connection produces a theory with 10+64 unknowns, which implies admitting torsion and possible nonmetricity. Our spacetimes are generalisations of classical pp-waves, four-dimensional Lorentzian spacetimes which admit a nonvanishing parallel spinor field. We generalize this definition to metric compatible spacetimes with pp-metric and purely axial torsion. We compare these solutions with our previous results and other solutions of classical models describing the interaction of gravitational and neutrino fields..