(Cornell), "Dark Energy: novel matter or gravity?" - cosmo 06


(Cornell), "Dark Energy: novel matter or gravity?" - cosmo 06

Dark Energy: novel matter or gravity?Rachel BeanCornell UniversityRecent paper:Axel de la Macorra (UNAM)Alessandro Melchiorri (Rome)Paolo Serra (Rome)Upcoming…David Bernat (Cornell)Eanna Flanagan (Cornell)Levon Pogosian (Simon Fraser)Alessandra Silvestri (Syracuse)Mark Trodden (Syracuse)Rachel Bean : COSMO ‘06 Sept 28th 2006 1/16

OverviewoCoupling of matter to scalar fields– Motivation– Observational issuesoInvestigating a coupling using cosmological and particle physics dataRachel Bean : COSMO ‘06 Sept 28th 2006 2/16

Why modify gravity?oTheories predict a modification!– Scalar-tensor gravityoWe don’t have a clue what dark energy is!– e.g. could be f(R) theories?– e.g. could contain higher geometric derivatives?oConceivably, we don’t yet have the correct large (and small?) scale theoryof gravity?Rachel Bean : COSMO ‘06 Sept 28th 2006 4/16

Tight constraints on gravity from solar systemo f(R) theories -> Brans-Dicke with ! = 0– Inconsistent with solar system tests e.g. Cassini ! >20000 (" #= 2x10 $3 )oFuture constraints will be tighter– 2011 (?) GAIA could get " #< 10 $6– 2012 ESA Bepi-Columbo Mercury orbiter " #< 3x10 $5 , " %< 3x10 $4Rachel Bean : COSMO ‘06 Sept 28th 2006 5/16Figure: Takeshi Chiba

Modified gravity -> time varying Go BBN abundances (Copi, Davis, Krauss 2003)– z= 10 10+0.20– G/G 0= 1.01 (68%)-0.16oLunar radar ranging– z=0– dG/dt/G

Change to G Change to massesConformal equivalence: non-minimal couplings gravity and to matterRedefinition of the metric (F’’(&)! 0)Scalar field redefinition gives us canonical scalar field LagrangianRachel Bean : COSMO ‘06 Sept 28th 2006 7/16Takeshi Chiba (2003)

Can evade solar system constraintsoDifferent couplings to CDM and baryons can avoid this– e.g. coupling to trace of T µ'(cdm) (Amendola 1999, Bean & Magueijo 2000)V effVe C&oDensity dependent coupling to baryonic and CDM objects– e.g. ‘Chameleon fields’ (Khoury & Weltman 2003, Mota & Davis 2006)&– Must test gravity/ equivalence principle in different density backgrounds todetect thisRachel Bean : COSMO ‘06 Sept 28th 2006 8/16

Stability issues in coupled theorieso Adiabatic behavior if slow evolution of the Hamiltonian of the system (M EFF2>> H O -2 )oCan lead to critical shift in clustering behavior of the scalar field theory theoryNon-adiabaticAdiabatic(Quintessence)Stable in typical theories c s2>0Can be unstable c a2

Learning about matter/ dark energy couplingsoPossibility of links between matter and otherwise weakly interacting field offersinteresting options– solar system tests– gravitational collapse instabilities on astrophysical scales– Cosmological large scale structure implicationsoIf coupling involves standard model particles– we don’t just only rely on indirect cosmological/astrophysical observations– Also should consider evidence from direct particle physics measurements.Rachel Bean : COSMO ‘06 Sept 28th 2006 10/16

Investigating a coupling to neutrinosoConsider a simple scalar field model coupled to neutrinosoThen a relationship between neutrinos and dark energy would lead tovariations in the apparent equation of stateRachel Bean : COSMO ‘06 Sept 28th 2006 11/16de la Macorra, Melchiorri, Serra, RB (2006)

Utilizing ‘direct’ neutrino mass dataoKinematics-missing momentum and energy– tritium beta decay, 3H -> 3He + e- + ne,– or pion decay, ( + $> µ + + ' µoNeutrino oscillations– determine )m 2 using P(' l-> ' l’) = sin 2 2* sin2()m 2 L/E ')oExchange of virtual neutrinos,e.g. 0'%% +`neutrinoless beta decay’– If (anti) neutrino has non-zero mass– If neutinos are majoranaRachel Bean : COSMO ‘06 Sept 28th 2006 12/16

Neutrinoless double beta decayoNeutrinoless double beta decay is the only known process that enables to testexperimentally– the Majorana nature of neutrino– together with its absolute mass scale.oMakes this topic very attractive!oThe half life time is given by the following formula:(T 1/2,0!) -1 = a 0!F 0!|M 0!| 2 " 2 / log(2)Where:a 0! ~ 5x10 -17 yr -1 is a dimensional factorF 0! is a known phase space factor proportional to Q ##5M 0! is the nuclear matrix element (n.m.e.)." = /m e with being the effective mass of the exchanged neutrino and m ethe mass of the electron (0.511 MeV/c 2 ).Rachel Bean : COSMO ‘06 Sept 28th 2006 13/16

The Moscow-Heidelberg 0v%% resultsooPhys. Lett. B586, 198 (2004); hep-ph/0404088Nucl.Instrum.Meth. A522 (2004) 371-406 hep-ph/0403018– 71.7 kg yr,– 11kg enriched 76 Ge (equivalent to a ton of normal 76 H.V. Klapdor-Kleingrothaus, A. Dietz, I.V.Ge) Krivosheina, O. Chkvorets hep-ph/0403018– 28.75 ± 6.86 events at 2039 keV, the Q-value for 0'%% decay (reported as 4.2" now 6")This is interpreted as T 1/2= 1.15 -0.5+2.99x 10 25 y– Given matrix element (Rodin, Faessler, Simkovic, Vogel 2006) this translates into0.43< m %%< 0.81 (95% CL)– Applying this to the cosmological neutrino density0.0137 < , v h 2 < 0.026 (95% CL)ooTo confirm or reject the KDHK claim of the 0'%% discovery convincingly one needs 5-10 kmoleyearsexposure with low background (source: Petr Vogel Fermilab presentation 2004).KATRIN (Karlsruhe Tritium Neutrino experiment) in the next decade )m '~ 0.2eVRachel Bean : COSMO ‘06 Sept 28th 2006 14/16

Combining cosmological and particle measurementsRachel Bean : COSMO ‘06 Sept 28th 2006 15/16de la Macorra, Melchiorri, Serra, RB (2006)

ConclusionsoCoupling between dark energy and matter is theoretically conceivableoAlthough Solar System bounds can offer tight PPN constraints, sometheories can evade theseoIssues about stability have and are being addressedoFuture insights into coupling can be gained from combining astrophysical(indirect) observations with direct particle physics investigations of the SM.oInteresting discord between indirect and direct measurements– Signaling new physics?– Complementary and increased precision measurements in near futureRachel Bean : COSMO ‘06 Sept 28th 2006 16/16

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