We show that the fluctuations of quantum fields as seen by late comoving
observers are significantly influenced by the history of the early Universe,
and therefore they transmit information about the nature of spacetime in
timescales when quantum gravitational effects were non-negligible. We discuss
how this may be observable even nowadays, and thus used to build falsifiability
tests of quantum gravity theories.Comment: 3 pages. 2 Figures. Proceedings Theory Canada 9. Published in
  Canadian Journal of Physics.
  (http://www.nrcresearchpress.com/doi/abs/10.1139/cjp-2014-0567

Blasco, Ana

Garay, Luis J.

Martin-Benito, Mercedes

Martin-Martinez, Eduardo

English

arXiv

Jarramplas 2014 ; Presentación en Power Point: 17 diapositivasPeer Reviewe

Martín-Benito, Mercedes

Garay, Luis Javier

Martín-Martínez, Eduardo

Digital.CSIC

!The Quantum Echo  of  the Early UniverseJARRAMPLAS 2014!Mercedes Martín-Benito !Radboud University Nijmegen !!in collaboration with  Ana Blasco (UCM), Luis J. Garay (UCM/IEM-CSIC), Eduardo Martín-Martínez (IQC-UW/PI) !Looking for Signatures of  QG today - To test proposals for Quantum Gravity we need - QG scales out of  reach of  experiments on earth - Most promising window: COSMOLOGYi) predictions ii) experimental data encoding QG effects Looking for Signatures of  QG today - Evidence of  early Universe physics imprinted onto the CMB - Primordial gravitational waves     carry information of  the quantum     fluctuations of  the geometry of  the     early Universe“The long search of  B-modes is apparently over and a new era of  B-mode cosmology has begun”Looking for Signatures of  QG today - Have QG signatures really survived from the early Universe          all the way to our current era? - If  so, how strong are they? - Will it be possible to validate or falsify different QG proposals             by looking at the data?We explore a simple way, based on a toy model, to assess the strength of  the quantum signatures of  the early Universe that might be observed nowadaysSetting - We will analyze Gibbons-Hawking effect :     Creation of  particles measured by a particle     detector due to cosmological expansion when     the surrounding matter fields are in vacuum - Particle detector coupled to matter fields from the early stages of  the     Universe until today:Would the detector conserve any information from the time when it witnessed the very early Universe dynamics?tPl ⇠ 10 44s ; T ⇠ 1017s - We will analyze Gibbons-Hawking effect :     Creation of  particles measured by a particle     detector due to cosmological expansion when     the surrounding matter fields are in vacuum - Particle detector coupled to matter fields from the early stages of  the     Universe until today:Would the detector conserve any information from the time when it witnessed the very early Universe dynamics?YES             tPl ⇠ 10 44s ; T ⇠ 1017sSettingEarly Universe dynamics' - Flat FRW with T3 topology and matter source a massless scalar - We will compare the response of  the detector evolving under two     different Universe dynamics which disagree only during the short     time when matter-energy densities are of  the order the Planck scaleEarly Universe dynamics'2 4 6 8 105101520a(t)Ltac(t) =(12⇡G⇡2')1/6Lt1/3.aq(t) =lL ⇡2'12⇡G!1/6 "1 +✓12⇡Gl3◆2t2#1/6.GR vs Effective LQCl ~  quantum of  lengthL ~  compactification scale - Flat FRW with T3 topology and matter source a massless scalar - We will compare the response of  the detector evolving under two     different Universe dynamics which disagree only during the short     time when matter-energy densities are of  the order the Planck scaleGibbons-Hawking effect - We consider a massless scalar field     in the conformal vacuum - The proper time of  comoving observers (who see an isotropic     expansion) does not coincide with the conformal time ⌘c(t) =3L t2/32(12⇡G⇡2')1/6 ! ⌘c(t) +  t  l3/(12⇡G)⌘q(t) =Ll✓12⇡G⇡2'◆1/6t · 2F1"16,12,32, ✓12⇡Gl3t◆2#The Unruh -De Witt model⌦|0i =   |ei|ei =  +|0iproper time of  the detector (comoving)coupling strengthswitching functionworld-line of  the detector (stationary)HˆI(t) =    (t)( +ei⌦t +   e i⌦t) ˆ[~x0, ⌘(t)]t  (t)[~x0, ⌘(t)]Probability of  excitation -       : field in the conformal vacuum and detector in its ground stateT0 - Transition probability for the detector to be excited at time     :T At leading order  (    small enough) Pe(T0, T ) =  2X~n|I~n(T0, T )|2 +O( 4)I~n(T0, T ) =Z TT0dt (t)a(t)p2!~nL3e 2⇡i~n·~x0L ei[⌦t+!~n⌘(t)]!~n =2⇡L|~n|~n = (nx, ny, nz) 2 Z3  ~0Probabilities: GR vs effective LQCIc~n(T0, T ) = Ic~n(T0, Tm) + Ic~n(Tm, T )Iq~n(T0, T ) = Iq~n(T0, Tm) + ei!~n Ic~n(Tm, T )⌘q(Tm) ⇡ ⌘c(Tm) +   Pe(T0, T ) ⌘ P qe (T0, T )  P ce (T0, T ) - We split the integrals - Difference of  probabilities Pe(T0, T ) =  2X~n   Iq~n(T0, Tm)  2   |Ic~n(T0, Tm)|2+2Re⇣ he i !~nIq~n(T0, Tm)  Ic~n(T0, Tm)i⌘ Ic~n⇤(Tm, T )Probabilities: GR vs effective LQCIc~n(T0, T ) = Ic~n(T0, Tm) + Ic~n(Tm, T )Iq~n(T0, T ) = Iq~n(T0, Tm) + ei!~n Ic~n(Tm, T )⌘q(Tm) ⇡ ⌘c(Tm) +   Pe(T0, T ) ⌘ P qe (T0, T )  P ce (T0, T ) - We split the integrals - Difference of  probabilities Pe(T0, T ) =  2X~n   Iq~n(T0, Tm)  2   |Ic~n(T0, Tm)|2+2Re⇣ he i !~nIq~n(T0, Tm)  Ic~n(T0, Tm)i⌘ Ic~n⇤(Tm, T )The relative difference on the detector's particle counting in both scenarios will be appreciably different even for long  T    Sensitivity with the quantum parameters - Any observations we may make on particle detectors will be averaged     in time over many Planck timeshPe(T0, T )iT =1TZ TT TPe(T0, T0) dT 0 T   l3/(12⇡G) - Sub-Planckian detector ⌦⌧ 12⇡G/l3E =⌧ h Pe(T0, T )iThPGRe (T0, T )iT  T T = T   Tlate T, Tlate   l3/(12⇡G) - Estimator to study sensitivity with quantum of  lengthSensitivity with the quantum parametersE =⌧ h Pe(T0, T )iThPGRe (T0, T )iT  T0.5 1.0 1.5 2.0 2.510-910-710-50.001ElExponential with the size of  the spacetime quantum T     - Cosmological observations could put stringent upper bounds to  lConclussions - Although this is a toy model, it captures the essence of  a key     phenomenon: Quantum field fluctuations are extremely sensitive to     the physics of  the early Universe.  !!-  The signatures of  these fluctuations survive in the current era with a      significant strength. !!-  We showed how the existence (or not) of  a quantum bounce leaves      a trace in the background quantum noise that is not damped and        would be non-negligible even nowadays. !!-  The use of  LQC in this derivation is anecdotical, and we believe      that our main result is general:The response of  a particle detector today carries the imprint of  the specic dynamics of  the spacetime in the early UniverseThanks for your attention!

The Quantum Echo of the Early Universe

Blasco, A.

Garay, L.J.

Martín-Benito, M.

Martin-Martinez, E.

NARCIS 

The quantum echo of the early universe

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