Federico Piazza

Federico Piazza's picture

Research Interests

For many years advances in fundamental physics consisted in pushing the high energy limit of our knowledge higher and higher. In the last decade, cosmology has been flooded with such an amount of high precision data that a new, 'low energy path' to the mysteries of nature is now at hand. My research in cosmology focuses mainly on the two periods of accelerated expansion that our data strongly indicate and that are calling for a deeper understanding.

Inflation is an excellent low energy window on the highest energies. I worked on primordial non-gaussianities and models with varying speed of sound. I am very interested in fundamental aspects such as the relation between symmetries in inflationary theories and the almost scale invariance of the observed power spectrum.

Dark energy (the current acceleration of the universe), rather than just a low energy window seems to insinuate that some new unraveled physics is effective already at unexpectedly low energies. Such an amazing phenomenon may suggest that the standard low-energy framework `gravity+matter fields' is just inadequate and needs to be modified. I proposed an infrared modification of general relativity dictated by an 'ultra strong' version of the equivalence principle that seem to ease also other difficulties such as the cosmological constant problem and the black hole information paradox.

Violations of the (standard!) equivalence principle and gravitational phenomenology are another main branch of my research. I worked both on string-inspired model (the `runaway dilaton') and on simple scalar extension of the standard model (the 'higgs portal').

I also worked at the intersection between gravity and quantum information and considered regions of space as quantum subsystems as a way to generalize the standard framework of semi-classical gravity.

Positions Held

  • 2005 - 2006 Marie Curie Fellowship, Institute of Cosmology and Gravitation, University of Portsmouth.
  • 2003 - 2004 Post-doc, University of Milano Bicocca.


  • New Journal of Physics, Best of 2009: ``The IR-Completion of Gravity: What happens at Hubble Scales?'', F. Piazza, arXiv:0907.0765 [hep-th] New J. Phys. 11, 113050 (2009)
  • Honorable Mention at the Gravity Research Foundation essay competition 2009 with an essay of the title ``Modifying Gravity in the Infra-Red by imposing an 'Ultra-Strong' Equivalence Principle'', F. Piazza, Int. J. Mod. Phys. D 18, 2181 (2009) arXiv:0904.4299 [hep-th]

Recent Publications

  • Bimetric structure formation: non-Gaussian predictions, J. Magueijo, J. Noller and F. Piazza, Phys. Rev. D 82, 043521 (2010) arXiv: 1006.3216
  • Sub-eV scalar dark matter through the super-renormalizable Higgs portal, Federico Piazza, Maxim Pospelov, Phys. Rev. D 82, 043533 (2010) arxiv:hep-ph/1003.2313
  • The universe is accelerating. Do we need a new mass scale? S. Nesseris, F. Piazza and S. Tsujikawa, Phys. Lett. B 689, 122 (2010) arXiv: 0910.3949
  • The IR-Completion of Gravity: What happens at Hubble Scales? F. Piazza, New J. Phys. 11, 113050 (2009) arXiv: 0907.0765
  • Modifying Gravity in the Infra-Red by imposing an 'Ultra-Strong' Equivalence Principle, F.~Piazza, Int. J. Mod. Phys. D {\bf 18}, 2181 (2009) arXiv: 0904.4299
  • Rapidly-Varying Speed of Sound, Scale Invariance and Non-Gaussian Signatures, Justin Khoury, Federico Piazza, JCAP 0907, 026 (2009) arxiv:hep-th/0811.3633
  • Renormalized Thermal Entropy in Field Theory, Sergio Cacciatori, Fabio Costa, Federico Piazza, Phys. Rev. D79, 025006 (2009) arxiv:hep-th/0803.4087
  • Modelling a Particle Detector in Field Theory, Fabio Costa, Federico Piazza, New J. Phys. 11, 113006 (2009) arxiv:hep-th/0805.0806
  • Measuring deviations from a cosmological constant: a field-space parameterization, Robert Crittenden, Elisabetta Majerotto, Federico Piazza, Phys. Rev. Lett. 98, 251301 (2007) arxiv:astro-ph/702003
  • Luca Amendola, M. Gasperini, Federico Piazza, SNLS data are consistent with acceleration at z=3, Phys.Rev. D74 (2006) 127302, arxiv:astro-ph/610574
  • Gauss-Codazzi thermodynamics on the timelike screen, Federico Piazza, arXiv: 1005.5151
  • New views on the low-energy side of gravity, Federico Piazza, arXiv: 0910.4677. Review of several talks given in recent years (4th International Workshop DICE2008: From Quantum Mechanics through Complexity to Spacetime: The Role of Emergent Dynamical Structures, Castiglioncello, Italy, 22-26 Sep 2008 and talk given at Emergent Gravity IV, Vancouver, BC, Canada, 24-28 Aug 2009 and talk given at Emergent Gravity, Cambridge, Massachusetts, 25-29 Aug 2008)
  • Volumes of Space as Subsystems, Federico Piazza, Fabio Costa, PoS(QG-Ph)032, Proceedings of ``From Quantum to Emergent Gravity: Theory and Phenomenology'' arxiv:gr-qc/0711.3048


  • ``Modifying Gravity in the Infra-Red by imposing an Ultra-Strong equivalence principle" -- ``Emergent Gravity IV" August 24-28 2009, University of British Columbia, Vancouver (invited contribution) -- IHES, Paris, March 23, 2010 -- Imperial College, London, 16/12/2009 -- Department of Physics, University of Columbia, NY, 07/12/2009 -- CITA, Toronto, 30/10/2009 -- Department of Physics, University of Philadelphia, 09/09/2009 -- Department of Physics, University of Milan Bicocca, July 2009.
  • ``Scale invariant spectrum and rapidly varying speed of sound'' - PI-CITA day, Toronto, 19/5/2009 -- Workshop ``New Horizons for Modern Cosmology" Galileo Galilei Institute, Florence (Italy), 2/2/2009 -- talk given at ICG, Portsmouth, 15/1/2009
  • ``Regions of space as subsystems: entropy and semiclassical gravity'' -- ``DICE2008", Castiglioncello (Italy), September 22-26, 2008 -- "From Quantum to Emergent Gravity: Theory and Phenomenology", SISSA, Trieste, June 11-15, 2007
  • ``Particle detector models, thermal entropy and localization'' -- (String Theory-) Seminar, Department of Physics, UCB, Berkeley, September 9, 2008
  • ``Which space-time actually emerges? The world as seen from inside a spin system'' -- ``Emergent Gravity", MIT, Boston, August 25-29, 2008 (invited contribution)
  • ``Particle Detectors, the Frog Principle and the Unruh Effect'' -- ``Hot topics in Modern Cosmology" Cargese (Corse) May 12-17, 2008
  • PIRSA:08090054, Particle detector models, entropy and localization in semiclassical gravity, 2008-09-04, Quantum Gravity
  • PIRSA:08090060, Particle detector models, entropy and localization in semiclassical gravity, 2008-09-04, Quantum Gravity
  • PIRSA:08070013, Coupling variations and equivalence principle violations in string inspired scenarios, 2008-07-15, In Search for Variations of Fundamental Couplings and Mass Scales
  • PIRSA:08040072, Particle Detector Model Questions the Unruh Effect, 2008-04-30, Perimeter Institute Quantum Discussions
  • PIRSA:06010010, Spacetime regions as "quantum subsystems": glimmers of a pre-geometric perspective, 2006-01-19, Quantum Gravity
  • PIRSA:06010005, Gravity and cosmology of the dilaton at "strong coupling", 2006-01-17, Cosmology
  • PIRSA:04050000, Modifying Gravity in the Infra-Red by imposing an Ultra-Strong equivalence principle., 2004-05-27, New Prospects for Solving the Cosmological Constant Problem