Noticias

23/11/2021

Direct links to the talks: 

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Though still struggling with the COVID-19 nightmare, we are back and ready to face a new edition of the Valencia Winter Workshop on Theoretical Physics. This time this event will take place at the Seminar Room of the Department of Theoretical Physics of the University of Valencia and, at the same time, it will be broadcasted live from our BigBlueButton meeting room and also via our YouTube channel. On site and online participation is thus very welcome. 

Like in previous editions, this meeting is intended to bring together researchers with common interests on the geometric structure of space-time, quantum properties of gravity, cosmology, and astrophysics who collaborate with the host group via active projects (FunFiCO-777740, i-COOP20462, PROMETEO 2020/079, FIS2017-84440-C2- 1-P,  PID2020-116567GB-C21, …) or have close ties with them. 

Fundamental questions about the foundations of gravitation, the role of quantized fields in curved space-times, cosmological and astrophysical signatures of gravity within and beyond General Relativity, and recent developments on other topics, will be reviewed in a series of invited/contributed talks, and open discussions. 

The idea of the workshop is to encourage everyone, from seniors to less-experienced students and postdocs, to present some results obtained during the year 2021 that they find particularly relevant/interesting/easy to discuss in a relaxed atmosphere, possibly using the pdf of a paper already on arXiv or some scanned handwritten notes of a current work in progress, and addressing a few simple questions: 

  1. What is it about?
  2. Why is it important? (An explanation of what is unique and/or timely about this topic and the difference it might make with respect to previous work). 
  3. Perspectives. 

The contributions are NOT expected to last 60 minutes. Rather 15-25 minute conceptual presentations with minimal calculations (if possible) are encouraged for everyone. The subsequent discussion and questions could extend as much as needed, depending on the audience participation. To be more concrete, for students we expect talks of about 20' (+10' of discussion), and for postdocs/seniors up to 30'(+15' of discussion) at most. All non-essential calculations could be provided to those interested for their individual analysis. The idea is to have talks not too focused on technicalities (if the topic allows, obviously) but have more discussions which could lead to new works/collaborations in 2022 and beyond. 

The workshop programme appears below: Click on each item for more information.  

If you are an online speaker or simply want to participate in the discussions, please join us via BigBlueButton (no need to install anything, just click).

ORGANIZING COMMITTEE:

  • Flavio Bombacigno.
  • Florencia A. Teppa Pannia.
  • Gonzalo J. Olmo.  
  • Andreu S. Masó. 
  • Antonio Ferreiro de Aguiar.
  • Sergi Nadal. 
  • Adrià Delhom I Latorre. 
  • Pau Beltrán Palau.

This meeting is organized by the Quantum Black Holes, Supergravity and Cosmology group at the Department of Theoretical Physics & IFIC of the University of Valencia & CSIC, Spain.

Photo of this post by  Pepe Serrador, CC BY-SA 4.0 , via Wikimedia Commons.

10/11/2021

In the year 2020 the UV-QG group started a collaboration with members of the University of Cape Town (UCT) at the Department of Mathematics and Applied Mathematics, and the UCT Astrophysics, Cosmology and Gravity Centre (ACGC). This collaboration was possible thanks to the economic support of the internationalization program i-COOP of CSIC through the grant COOPB20462. 

As part of the activities of this project, in December 2020 members of UCT participated in our 4th Valencia Winter Workshop, and in May 2021 we organized for them the 1st i-School and Conference on Metric-Affine Gravity, both of which were held completely online due to mobility restrictions caused by the COVID-19 epidemics. 

Now that vaccines are allowing some relaxation on international mobility, two members of the UCT team, namely, Dr. Álvaro de la Cruz Dombriz and Dr. Jahed Abedi, will visit us in Valencia during the week of November 15-19, 2021. For this occasion, we are organizing a Workshop on Black Holes, Cosmology, and Metric-Affine Gravity, which will take place in a hybrid format on November 18-19. Some talks will be delivered at the Seminar Room of the Department of Theoretical Physics of the University of Valencia in Burjassot and others will be delivered remotely. As usual, everything will be broadcasted live from our Big Blue Button meeting room and also via our YouTube channel

Besides our colleagues from UCT, this week we will also have Dr. Fabio Moretti (Sapienza, Università di Roma), who will also join us for this event. Dr. Moretti collaborates with Simon Boudet (visiting us from September to December, 2021), Flavio Bombacigno, and Gonzalo J. Olmo on topics related with metric-affine gravity and gravitational waves. 

If you want to know more about our special guests of this event, here you have a short bio of them: 

Dr. Álvaro de la Cruz Dombriz:  images.ashx?id=136

Since August 2015, Álvaro (Aranjuez, 1980) has been a Faculty Lecturer in the Department of Mathematics and Applied Mathematics at the University of Cape Town (UCT) and a member of the UCT Astrophysics, Cosmology and Gravity Centre (ACGC) at UCT. Previously, awarded a PhD at the Complutense University of Madrid (2010, Summa cum Laude) on theoretical and observational constraints in extended theories of gravity. Subsequently held a postdoctoral fellow post at the UCT Cosmology and Gravity group and obtained a Marie Curie postdoctoral contract at the ICE-IEEC Barcelona. 

Álvaro’s publications include more than 50 peer-reviewed articles with seminal contributions in the areas of cosmological large-scale structures, foundations of theories beyond Einsteinian gravity, particularly on Scalar-Tensor gravity theories, and indirect methods of dark matter detections.

To date, Álvaro has been member of the scientific teams for seventeen research funded projects. Since 2016 he has been a member of two running EU-COST actions and along the course of his career he has been the Principal Investigator (PI) for six funded research projects in both Europe and South Africa.

In 2017 he was appointed as an Associate in the SKA Cosmology and Gravitational Waves collaboration and was honoured with the Young Researcher Award, (UCT College of Fellows, 2017) and the Claude Leon Foundation Merit Award for Early-career Researchers (2018).

Dr. Jahed Abedi: images.ashx?id=137

Jahed Abedi, a postdoctoral researcher from UCT and University of Stavanger, is a black hole physicist, working on gravitational physics in both observational side such as searching for GW echoes and QNMs in LIGO/Virgo data and theoretical side such as BH perturbations, QNMs, and QFT in curved space-time.
 

images.ashx?id=143Dr. Fabio Moretti: 

Fabio Moretti obtained his PhD in 2021 at the University of Rome "La Sapienza", with a thesis on gravitational waves in modified theory of gravity. His principal interests cover propagation and interaction of gravitational waves with astrophysical media in extensions of general relativity, with special emphasis on additional polarizations and settling of dispersive/dissipative phenomena. He is also involved in compact objects physics, where he mainly deals with the role of additional scalar degrees of freedom in stellar structure and evolution.

 

The workshop programme appears below. Click on each item for more information.  

 

If you are an online speaker or simply want to participate in the discussions, please join us via BigBlueButton (no need to install anything, just click).

Direct links to the talks: 

 images.ashx?id=113

images.ashx?id=114

 

 

ORGANIZING COMMITTEE:

  • Flavio Bombacigno. 
  • Florencia A. Teppa Pannia.
  • Andreu Masó.
  • Gonzalo J. Olmo.
  • Silvia Pla García. 

  images.ashx?id=111  images.ashx?id=112

 

Photo of this post by Andreas Selter on Unsplash

23/10/2021

Esta semana el programa Pegando la Hebra de Plaza Radio ha entrevistado a nuestra compañera María A. Lledó (Marian). En esta entrevista habla de sus dos pasiones: la física teórica y la poesía.

No os perdáis su descripción de la teoría de cuerdas, de los problemas entre teoría cuántica y relatividad general, y otras cuestiones relacionadas con agujeros negros y el espacio-tiempo.  

Para escucharlo, haz click sobre esta imagen:

images.ashx?id=132

 

Photo de cabecera by Alina Grubnyak on Unsplash 

18/10/2021

Particle trajectories in metric affine spacetimes: observing torsion with a WKB approach.

We are pleased to initiate our seminar session this year with a talk by our colleague Simon Boudet, who will be visiting our Department until the end of December 2021. 

Simon got his master degree at the university of Rome" La Sapienza" in 2019, with a thesis entitled "Implementation of Ashtekar variables in the Palatini f(R) theory of gravity", where he dealt with a generalization of the Loop Quantum Gravity formalism to scalar tensor theories. Currently, his research activity mainly focuses on classical and semiclassical aspects of metric affine models of gravity, with special emphasis on compact objects physic and cosmological implementations.

The title and abstract of his talk are the following: 

TITLE: Particle trajectories in metric affine spacetimes: observing torsion with a WKB approach.

ABSTRACT: In this talk I will review some aspects of trajectories followed by test particles in metric affine theories of gravity. Firstly, I will introduce the notions of geodesic motion and autoparallel paths, showing as within an eikonal  approximation photon do not carry information about torsion and nonmetricity. Then, I will discuss the case of fermions, and I will derive, according a WKB method, the modification induced by torsion to geodesic trajectories. Finally, I will briefly sketch some hypothetically observable phenomena related to neutrinos.

Coordinates: Tuesday October 19th at 10:30 in the seminar room of the Theoretical Physics Department.

Follow this session online via BigBlueButton.

Also on our YouTube channel

Photo by Solen Feyissa on Unsplash

08/05/2021

We are very happy to announce that in March 2021, our colleague Adrià Delhom i Latorre received a notificacion from the Institute of Physics (IoP) to let him know he had been named "Trusted Reviewer". According to the IoP website, "Achieving ‘IOP trusted reviewer’ status demonstrates an exceptionally high level of peer review competency".  Below he tells us in his own words about his experience in the refereeing process. Our most sincere Congratulations, Adri! 

During the first two years of my PhD I have been gaining experience in publishing research papers, both with collaborators and alone. At some point, I received my first request for being the reviewer of a pre-print that was submitted for Physics Letters B, a journal where I had published a couple of papers before. Although I am not sure how this happened, I guess that it was through an (anonymous) colleague, who noticed my works and thought that I could be a good reviewer for that related work, hence recommending my nomination to the editor whenever she/he has to decline the offer to review it for her/his reasons (maybe lack of time?). In any case, I accepted to review the manuscript, which I ended up accepting as the authors carefully took into account my criticisms. Some time later, I received another request for reviewing an article, but this time for the journal Classical and Quantum Gravity, which belongs to IOP Science and where I have also published an article. The type of papers that are submitted to this journal are typically long and technical but, after a quick overall read, I though that I could do a good job as a reviewer, given that it was within my range of expertise. 

08/05/2021

The journal Universe has announced the winners of the Universe 2021 Best Paper Awards. All papers published from 2015 to 2020 in Universe were considered for the awards. After a thorough evaluation of the originality and significance of the papers, citations, and downloads, the following three winning papers, which were nominated by the Editor-in-Chief, have been selected: 

Nonsingular Black Holes in ƒ (R) Theories
By: Gonzalo J. Olmo and Diego Rubiera-Garcia
Universe 20151(2), 173–185

Is it no Longer Necessary to Test Cosmologies with Type Ia Supernovae?
By: Ram Gopal Vishwakarma and Jayant V. Narlikar
Universe 20184(6), 73

A Universe that Does Not Know the Time
By: João Magueijo and Lee Smolin
Universe 20195(3), 84

Review:

Seeing Black Holes: From the Computer to the Telescope
By: Jean-Pierre Luminet
Universe 20184(8), 86

 

We want to transmit our warmest congratulations to our group members Gonzalo J. Olmo and Diego Rubiera-Garcia on their achievement. 

The paper Nonsingular Black Holes in ƒ (R) Theories studies the structure of a family of static, spherically symmetric space-times generated by an anisotropic fluid and governed by a quadratic f(R) theory. Diego and Gonzalo found solutions that represent black holes with the central singularity replaced by a finite size wormhole, and showed that time-like geodesics and null geodesics with nonzero angular momentum never reach the wormhole throat due to an infinite potential barrier. For null radial geodesics, it takes an infinite affine time to reach the wormhole. This means that the resulting space-time is geodesically complete and, therefore, nonsingular despite the generic existence of curvature divergences at the wormhole throat. 

 

Main site photo by Lucian Alexe on Unsplash

Post photo by Lucian Alexe on Unsplash

28/04/2021

Direct links to the lectures: 

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We are pleased to announce that on May 4-7, 2021 we will host the 1st i-School and Conference on Metric-Affine Gravity, where the “i” stands for  “introductory,  informal, international“ and many other i-things the reader is i-nvited to i-nvent as an exercise.

Thanks to the support of the Spanish Research Council (CSIC) and its internationalisation programme i-COOP, in the year 2020 our UV-QG group started a collaboration with members of the Cosmology & Gravity group of the University of Cape Town (UCT) at South Africa. The difficulties imposed by the COVID-19 pandemic forced us to reshape the scientific plan and activities, which must be implemented in an online manner. Nothing new, as you all know. 

This online school has the following list of topics and lecturers: 

  • Flavio Bombacigno: The role of the Immirzi field in non-Riemannian spacetimes (3h).
  • Andreu Maso: Introduction to Python and numerical relativity (3h).
  • David Benisty:  Introduction to data analysis in cosmology with examples (in Python) (2h). 
  • Silvia Pla: Introduction to quantum particle creation in gravitational and electric backgrounds (3h).
  • Albert Petrov: Symmetry breaking in metric-affine gravity (3h).
  • Adrià Delhom: Introduction to unstable degrees of freedom and their implications in gravity (3h).

And additional talks will be given, among others, by: 

The lectures and talks of this event will be broadcasted live via  our YouTube channel. The corresponding link will be posted soon.

The meeting schedule appears next:

 

If you are a speaker or simply want to participate in the discussions, please join us via BigBlueButton (no need to install anything, just click).

ORGANIZING COMMITTEE:

  • Flavio Bombacigno.
  • Andreu Masó.
  • Gonzalo J. Olmo.
  • Silvia Pla García. 

  images.ashx?id=111  images.ashx?id=112

 

07/02/2021
Papers

In April 10, 2019 the Event Horizon Telescope collaboration released one of the most celebrated images of that year: a bright ring formed by the light and electromagnetic radiation that bends around a black hole with a mass that is 6500 million times that of the Sun. That image was in agreement with our expectations from what a (rotating) black hole should look like when surrounded by an accretion disk that emits electromagnetic radiation (light, heat, radio waves, ...). 

Black holes have an event horizon from which nothing can escape but they also have what is called a photon sphere, which is more external than the event horizon, and which represents a region in which photons are forced to orbit around the central object. If a photon gets sufficiently close to the black hole and crosses its photon sphere, then the photon orbit will fall following a spiral trajectory inwards until it falls within the event horizon. But if hits this boundary tangentially, then it could stay orbiting the central object for, in principle, an arbitrarily long time. Photons that get very close to the photon sphere but manage to scape after a long number of orbits will be able to reach us and provide evidence of the existence of this peculiar surface. Our detectors will perceive a (deformed) ring of intense radiation around a dark central region, which is known as black hole shadow. 

But photon spheres are not unique to black holes, and other compact astrophysical objects can also develop one. This is the case, in particular, of sufficiently compact wormholes, those hypothetical astrophysical objects that could be used to travel to distant regions of the universe by exploiting the topological properties of space-time. As a result, a wormhole surrounded by an accretion disk could also exhibit a bright ring in which radiation accumulates before escaping to reach us. 

A key difference between a wormhole and a black hole shadow is that light can scape from the wormhole, and this could make the internal region of the disk shadow brighter than in the black hole case since radiation emitted from the other side of the wormhole could reach us through it.

Like black holes, wormholes can have a mass and an electric charge. The funny thing of wormholes is that these two parameters need not be the same on both sides of these cosmic gates. As a result, the photon spheres on both sides could have different sizes and this necessarily has an impact on the properties of their shadows. In our work, we have analysed in some detail the conditions that allow for the existence of asymmetric thin-shell wormholes, formed by a thin shell of energy, and how the asymmetry affects their shadows according to observers on each side of them. 

Our analysis has been carried out in a gravitational context more general than Einstein's theory of gravity, the so-called f(R) theories of gravity in Palatini formalism. This mathematical scenario allows us to use the same external solutions as in Einstein's gravity but modifies the properties of the  energy shell that conforms the wormhole. The result is that stable configurations are possible and do not require exotic energy sources, which typically involve repulsive gravitational properties. The details can be found in a preprint posted in arXiv this week by our colleagues Mercè Guerrero, Gonzalo J. Olmo, and Diego Rubiera-García. 


Why is it important?

Our results are important because the universe contains hundreds of thousands of millions of galaxies and most of these structures are possible thanks to the existence of massive compact objects at their centres. Whether those compact objects are all black holes or more exotic entities is a matter that must be determined through observation. But in order to correctly interpret observational data, we must be able to estimate a range of different possibilities which are consistent with current theories. Observations will thus help us better understand what is physically possible and rule out theoretical alternatives.  

If the ring of light predicted by black holes is not always realised in nature and thicker structures or more than one thin ring are ever observed, then we could be facing the discovery of a kind of exotic astrophysical object that so far has only been found in the science fiction literature and movies. The implications that the existence of such objects could have for our understanding of the origin and evolution of the universe, and even for the development of future technologies are difficult to foresee. 


Perspectives

Our work has focused on the study of static, spherically symmetric wormholes with a certain mass and electric charge, but astrophysical objects are also rotating and may have deformations. Incorporating these new elements in the analysis will provide additional insights on new effects present in the shadows of compact objects, thus helping us refine our predictions and extract more valuable information from observational data. 

Read this paper on arXiv: e-Print: 2102.00840 [gr-qc]

 

Written by M. Guerrero, G.J. Olmo, and D. Rubiera-García. 

Photo by Ben Collins on Unsplash

23/01/2021

A fascinating lesson that follows from our current understanding of gravitational physics and quantum theory is that the large-scale structure of the universe cannot be fully understood without a clear description of its microscopic properties. This ultimately requires a consistent combination of gravity and quantum, a challenging endeavor that still remains one of the deepest open questions of theoretical physics.

The exploration of the early universe with high-precision technologies, the observation of gravitational waves generated by the coalescence of massive compact objects, the study of analog models of event horizons in the laboratory, the development of statistical techniques to address thermodynamic questions of black holes, and many other research lines and innovative approaches to longstanding questions are contributing to a growing body of knowledge that, sooner or later, will open new avenues to eventually find a successful theory that accurately describes the dynamics of gravitation in the strongest regimes.

Our group members Adrián del Río Vega, Eduardo J.S. Villaseñor, and Gonzalo J. Olmo are embarking in a new project with the Open Acess journal Symmetry with the hope of bringing together novel results on classical and quantum aspects of black holes and other compact objects, gravitational waves, early- and late-time cosmology, and different approaches to quantum gravity. We wish them good luck in this Special Issue entitle Black Holes, Cosmology, and Quantum Gravity

03/12/2020

Analizados nuevos datos sobre ondas gravitacionales

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03/12/2020

Online Meeting - Dec.14-18 

The fourth edition of the Valencia Winter Workshop on Theoretical Physics will take place online due to the COVID19 pandemics. Physical displacements must be reduced for sanitary reasons, but Physics must go on . 

Like in previous editions, this meeting is intended to bring together researchers with common interests on the geometric structure of space-time, quantum properties of gravity, cosmology, and astrophysics who collaborate with the host group via active projects (H2020-MSCA-RISE project FunFiCO-777740 or the i-COOP20462) or have close ties with them. 

Fundamental questions about the geometric foundations of gravitation, the role of quantized fields in curved space-times, cosmological and astrophysical signatures of gravity within and beyond General Relativity, and recent developments on other topics, will be reviewed in a series of talks with a high dosis of discussions. 

The idea of the workshop is to encourage everyone, from seniors to new students, to present some results obtained during the year 2020 that they find particularly relevant/interesting/easy to discuss in a relaxed way, possibly using the pdf of a paper already on arXiv or some scanned handwritten notes of a current work in progress, and addressing a few simple questions: 

  1. What is it about?
  2. Why is it important? (An explanation of what is unique and/or timely about this topic and the difference it might make with respect to previous work). 
  3. Perspectives. 

The contributions are NOT expected to last 60 minutes. Rather 15-25 minute conceptual presentations with minimal calculations are encouraged for everyone. The subsequent discussion and questions could extend up to 60' (in the case of senior researchers) or even more if necessary. For students we expect talks of about 20' (+10' of discussion), and for postdocs up to 30'(+15' of discussion) at most. All non-essential calculations could be provided to those interested for their individual analysis. The idea is to have talks not too focused on technicalities but have more discussions which could lead to new works/collaborations in 2021 and beyond. 

This meeting is organized by the Quantum Black Holes, Supergravity and Cosmologygroup at the Department of Theoretical Physics & IFIC of the University of Valencia & CSIC, Spain.

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