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8th to 12th March 2021

The main objective of the international workshop "Quantum Gravity, Higher Derivatives and Nonlocality" is to assess our current understanding of the interplay between gravity and quantum mechanics by discussing what is the main role of higher derivatives and nonlocality in the quantization of gravity, and whether they are really necessary to describe Nature at the fundamental level. In addition to discussing formal aspects of several approaches, applications of higher derivatives and nonlocality will be also explored, especially in the context of cosmology and black-hole physics.

Different schools of thought will be brought together, in such a way that everyone can benefit from fruitful discussions and learn from each other. In addition to individual talks, discussion sessions will help making the meeting more exciting and productive, so as to become the source of constructive debates and new insights, and to push our quantum-gravity community towards deeper understandings.

Download the flyer here.

**Luca Buoninfante**(Tokyo Inst. Tech., Chair)**Sravan K. Kumar**(Tokyo Inst. Tech.)

**Francesco Di Filippo**(YITP, Kyoto)**Alexey Koshelev**(Beira Interior, Covilhã)**Gaetano Lambiase**(Salerno and INFN)**João Marto**(Beira Interior, Covilhã)**Alessia Platania**(Perimeter Inst.)**Fabio Scardigli**(Milan Politecnico)**Masahide Yamaguchi**(Tokyo Inst. Tech.)

**Physics Dept., Tokyo Institute of Technology, Japan****Japan Society for the Promotion of Science (JSPS)****Physics Dept. "E.R. Caianiello", University of Salerno, Italy****Istituto Nazionale di Fisica Nucleare (INFN) - Gruppo Collegato di Salerno**

A vast amount of observational data has made Einstein's General Relativity (GR) the best current theory to describe classical aspects of the gravitational interaction. However, despite its great success there are still fundamental questions that remain unanswered. On short-distance scales GR predicts the existence of black-hole and cosmological big-bang singularities where spacetime terminates and the theory breaks down. Moreover, Einstein's theory lacks predictability in the high-energy regime, being perturbatively non-renormalizable. It is generally believed that a self-consistent theory of quantum gravity is necessary to deal with these issues and complete Einstein's GR in the short-distance and high-energy regimes.

A natural way to extend GR in the high-energy regime is to generalize the Einstein-Hilbert Lagrangian by adding higher powers of the curvature tensors and, indeed, in 1977 K. Stelle showed that quadratic curvatures were already sufficient to formulate a renormalizable theory of quantum gravity. However, such additional terms were also shown to introduce a **"ghost"** degree of freedom because of higher order time-derivatives which cause classical Hamiltonian instabilities and break unitarity at the quantum level. This moment in the history of Theoretical Physics - more than forty years ago - can be considered as the beginning of many new attempts aimed at formulating a consistent quantum theory of gravity, and thus at solving both issues of **renormalizability** and **unitarity** of the gravitational interaction.

To achieve a thorough assessment of the role and the true meaning of higher, or even infinite, derivatives in the quantization of gravity, in this workshop different point of views will be presented and several approaches to quantum gravity will be covered, among which

**Agravity****Asymptotically safe gravity****Effective field theory of gravity****Four-derivative gravity with unstable ghosts****Hořava-Lifshitz gravity****Metric-affine quantum gravity****Nonlocal theories of gravity****Self-completion of general relativity****String field theory**

Furthermore, applications of quantum gravity, higher derivatives and nonlocality will be discussed in the context of **cosmology**, **black-hole physics** and **spacetime singularities**.

**Irina Aref'eva**(Steklov Math. Inst., Moscow)**Andrei Barvinsky**(Lebedev Inst., Moscow)**Jens Boos**(William & Mary)**Robert Brandenberger**(McGill, Montreal)**Gianluca Calcagni**(CSIC, Madrid)**Xavier Calmet**(Sussex)**Claudia de Rham**(Imperial College London)**John Donoghue**(Massachusetts, Amherst)**Branko Dragovich**(Belgrade Inst. and Math. Inst. SANU)**Gia Dvali**(LMU, Munich)**Astrid Eichhorn**(Southern Denmark and CP3-origin)**Valeri Frolov**(Alberta)**Anish Ghoshal**(Tor Vergata and INFN)**Breno Giacchini**(SUSTech, Schenzhen)**Thomas Hertog**(KU Leuven)**Bob Holdom**(Toronto)**Olaf Hohm**(Humboldt, Berlin)**Gerard 't Hooft**(Utrecht)**<KEYNOTE>****Alexey Koshelev**(Beira Interior, Covilhã)**Nikolai Krasnikov**(INR, Moscow)**Philip Mannheim**(Connecticut)**Anupam Mazumdar**(VSI, Groningen)**Leonardo Modesto**(SUSTech, Schenzhen)**Roger Penrose**(Oxford)**<KEYNOTE>****Roberto Percacci**(SISSA, Trieste)**Alessia Platania**(Perimeter Inst., Waterloo)**Leslaw Rachwal**(Juiz de Fora)**Alberto Salvio**(Tor Vergata and INFN)**Frank Saueressig**(IMAPP, Nijmegen)**Ashoke Sen**(Harish-Chandra Res. Inst.)**Ilya Shapiro**(Juiz de Fora)**Alexei Starobinsky**(Landau Inst., Moscow)**Kellogg Stelle**(Imperial College London)**Anna Tokareva**(Jyväskylä)**Terry Tomboulis**(UCLA)**Richard Woodard**(Florida)**Masahide Yamaguchi**(Tokyo Inst. Tech.)**Andrei Zelnikov**(Alberta)

**Tirthabir Biswas**(Howard Hughes Medical Institute)**Robert Brandenberger**(McGill, Montreal)**Luca Buoninfante**(Tokyo Inst. Tech)**Francesco Di Filippo**(YITP)**Alexey Koshelev**(Beira Interior, Covilhã)**Sravan K. Kumar**(Tokyo Inst. Tech.)**João Marto**(Beira Interior, Covilhã)**Roberto Percacci**(SISSA, Trieste)**Alessia Platania**(Perimeter Inst., Waterloo)**Fabio Scardigli**(Milan Politecnino)**Richard Woodard**(Florida)**Masahide Yamaguchi**(Tokyo Inst. Tech.)

The time of the talks have been carefully chosen in order to be as suitable as possible for all the Invited Speakers, taking into account the fact that scientists from at least three different continents will participate in the Workshop.

Most of the talks will last * 30'+5'*, and few of them

You can find below the program with all the scheduled talks.

You can now download the abstracts.

Video recordings of the talks and discussion sessions can be found at this YouTube Channel.

**Session 1: Towards a (local) theory of quantum gravity
**

*Chair: Luca Buoninfante*

**12.30-12.50: Opening remarks****12:50-13:40***(40'+10'):***Gerard 't Hooft***[Negative energies in quantum gravity]***<KEYNOTE>***slides***13:40-14:15***(30'+5'):***John Donoghue***[The quantum field theory of quadratic gravity]**slides***14:15-14:50***(30'+5'):***Roberto Percacci***[Recent progress in Metric-Affine and Higher Derivative Gravity]*

*Chair: Luca Buoninfante & Richard Woodard*

**15:00-15:30***(30'):***Discussion session**

**Session 2: EFT of gravity, unitarity problem, Wilsonian vs non-Wilsonian UV completion**

*Chair: Alessia Platania*

**16:30-17:05***(30'+5'):***Claudia de Rham***[Positivity in gravitational theories]***17:05-17:40***(30'+5'):***Alberto Salvio***[Quadratic gravity]***17:40-18:15***(30'+5'):***Gia Dvali***[Saturons and QFT meaning of self-UV-completion via classicalization]***18:15-18:50***(30'+5'):***Philip Mannheim***[Solution to the ghost problem in higher derivative gravity]**slides***19:00-19:30***(30'):***Discussion session**

**Session 1: Asymptotic safety approach to gravity
**

*Chair: Roberto Percacci*

**13:00-13:35***(30'+5'):***Frank Saueressig***[Introducing form factors in asymptotically safe gravity]***13:35-14:10***(30'+5'):***Alessia Platania***[Non-perturbative unitarity and fictitious ghosts in quantum gravity]***14:10-14:45***(30'+5'):***Astrid Eichhorn***[Interplay of matter and quantum gravity]***14:55-15:25***(30'):***Discussion session**

**Session 2: String (field) theory, higher derivatives & nonlocality
**

*Chair: Alexey Koshelev*

**16:30-17:05***(30'+5'):***Ashoke Sen***[String field theory]***17:05-17:40***(30'+5'):***Irina Aref'eva***[Notes on Cauchy problem for nonlocal equations]***17:40-18:15***(30'+5'):***Branko Dragovich***[On nonlocality of p-adic and zeta strings]**slides***18:15-18:50***(30'+5'):***Olaf Hohm***[Duality and higher derivatives]***19:00-19:30***(30'):***Discussion session**

**Session 1: Higher derivatives, Lorentz (non)-invariance & (non)locality
**

*Chair: Masahide Yamaguchi*

**12:30-13:05***(30'+5'):***Andrei Barvinsky***[Lorentz non-invariance as the palladium of locality, unitarity and renormalizability in quantum gravity]**slides***13:05-13:40***(30'+5'):***Richard Woodard***[The case for nonlocal modifications of gravity]***13:40-14:15***(30'+5'):***Ilya Shapiro***[Exact renormalization group equations from the perturbative quantum gravity]***14:15-14:50***(30'+5'):***Leslaw Rachwal***[Higher derivative gauge theory as a toy-model for quantum gravity]**slides***15:00-15:30***(30'):***Discussion session**

**Session 2: Nonlocal theories of gravity
**

*Chair: Luca Buoninfante & Sravan Kumar*

**16:30-17:05***(30'+5'):***Nikolai Krasnikov***[Aspects of nonlocal field theories and gravity]***17:05-17:40***(30'+5'):***Alexey Koshelev***[Ghosts in ghost-free analytic infinite derivative gravity theories]**slides***17:40-18:15***(30'+5'):***Terry Tomboulis***[Nonlocal vertices, UV "opaqueness" and causality]***18:15-18:50***(30'+5'):***Leonardo Modesto***[Nonlocal quantum gravity]*

*Chair: Tirthabir Biswas, Luca Buoninfante & Sravan Kumar*

**19:00-19:30***(30'):***Discussion session**

**Session 1: Black holes, spacetime singularities & higher derivatives
**

*Chair: Francesco Di Filippo*

**12:30-13:00***(25'+5'):***Jens Boos***[Regular solutions in weak-field infinite-derivative theories: Green function approach]**slides***13:00-13:30***(25'+5'):***Breno Giacchini***[Regularization of Newtonian-limit singularities in higher-derivative gravity models]***13:30-14:05***(30'+5'):***Anupam Mazumdar***[Nonlocality in quantum gravity]***14:10-14:45***(30'+5'):***Xavier Calmet***[Quantum gravitational corrections to the entropy of a Schwarzschild black hole]***14:50-15:20***(30'):***Discussion session**

**Session 2: Black holes, spacetime singularities & higher derivatives
**

*Chair: Fabio Scardigli*

**15:45-16:35***(40'+10'):***Roger Penrose***[Why quantizing gravity cannot, on its own, solve the gravitational singularity problem]***<KEYNOTE>****16:35-17:10***(30'+5'):***Kellogg Stelle***[Black holes in higher derivative gravity]**slides***17:10-17:45***(30'+5'):***Valeri Frolov***[Remarks on nonsingular black holes]**slides***17:45-18:05***(20'):***Short break [discussions are welcome]****18:05-18:40***(30'+5'):***Bob Holdom***[Ultraviolet completion and not quite black holes]***18:40-19:15***(30'+5'):***Andrei Zelnikov***[Ghost free modification of the Polyakov action and 2D black holes]*

*Chair: Francesco Di Filippo & Fabio Scardigli*

**19:20-19:50***(30'):***Discussion session**

**Session 1: Cosmology, higher derivatives & nonlocality
**

*Chair: Sravan Kumar*

**13:00-13:35***(30'+5'):***Alexei Starobinsky***[Geometric inflationary models based on higher-derivative gravity]**slides***13:35-14:10***(30'+5'):***Masahide Yamaguchi***[Cosmological perturbations in Palatini formalism]**slides***14:10-14:45***(30'+5'):***Robert Brandenberger***[String cosmology and the breakdown of local effective field theory]*

*Chair: Sravan Kumar & João Marto*

**14:55-15:25***(30'):***Discussion session**

**Session 2: Cosmology, higher derivatives & nonlocality
**

*Chair: Robert Brandenberger*

**16:30-17:05***(30'+5'):***Thomas Hertog***[Observational signatures of novel variations on Starobinsky inflation]***17:05-17:40***(30'+5'):***Gianluca Calcagni***[Stochastic gravitational-wave background in quantum gravity]***17:40-18:10***(25'+5'):***Anna Tokareva***[UV properties of nonlocal scalar theories]***18:10-18:40***(25'+5'):***Anish Ghoshal***[UV-completion in particle theory with infinite derivatives: conformal Invariance, laboratory, and cosmological implications]*

*Chair: Robert Brandenberger, Luca Buoninfante & Sravan Kumar*

**18:50-19:40***(50'):***Final discussion session with all the speakers of the Workshop**

*Chair: Luca Buoninfante & Sravan Kumar*

**19:40-19:50***(10'):***Concluding remarks & outlook**

*Last updated on March 8, 2021*

The International Workshop "Quantum Gravity, Higher Derivatives and Nonlocality" will be held online on the **Meeting Platform Zoom**, from 8th to 12th March, 2021. The Zoom links will be sent to all the participants by e-mail few weeks in advance.

For any type of question and/or clarification, please contact the Organizing Committee:

**Luca Buoninfante**(Tokyo Inst. Tech., Chair)

buoninfante.l.aa AT m.titech.ac.jp**Sravan K. Kumar**(Tokyo Inst. Tech.)

sravan.k.aa AT m.titech.ac.jp