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Baryon density of the Universe : a trace of a scalar field?

Albert Einstein Century Conference July, 20 th 2005 Paris, Palais de l'Unesco. Julien Larena * , Jean-Michel Alimi * , Arturo Serna‡. * LUTh, Observatoire de Paris-Meudon, FRANCE ‡Departamiento de física, Universidad Miguel Hernández, Elche, SPAIN. Baryon density of the Universe :

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Baryon density of the Universe : a trace of a scalar field?

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  1. Albert Einstein Century Conference July, 20th 2005 Paris, Palais de l'Unesco Julien Larena* , Jean-Michel Alimi* , Arturo Serna‡ *LUTh, Observatoire de Paris-Meudon, FRANCE ‡Departamiento de física, Universidad Miguel Hernández, Elche, SPAIN Baryon density of the Universe : a trace of a scalar field?

  2. Primordial Nucleosynthesis Synthesis of the lightest elements : D, 3He, 4He and traces of 7Li Energy scale : 10 MeV to a few keV Complex network of nuclear reactions (28 reactions) Standard nuclear physics is supposed to apply Two main parameters : h10 and H(T) Hubble parameter : Expansion rate Baryon to photon ratio Reaction rate : G (T, h10)=Cross section (T) × number densities(h10,T) Thermal equilibrium : G/H > 1 Frozen abundances : G/H < 1

  3. Then, the predicted primordial abundances are : And the observed ones : Good agreement ! Large discrepancy Ryan & al., 2000, ApJ Lett.; Bonifacio & al., 2002,A&A Luridiana & al., 2003, ApJ; Izotov & al., 1999, ApJ Kirkman & al., 2003, ApJ Cybert & al.,2004, PRD CMB Experiments : WMAP alone : (WMAP+CBI+ACBAR) + Lya + 2dF Wbh2=0.0224±0.0009 orh10= 6.14±0.25 Tegmark & al,2004,PRD Spergel & al, 2003, ApJ Citer les ref

  4. Universal coupling  Metric theories : Weak Equivalence Principle holds Jordan-Fierz frame : Our parameterization : Scalar-tensorcosmology Einstein frame : Observable quantities must be computed in the Jordan frame.

  5. General Relativity : Observable expansion rate : with Speed-up factor : Effective gravitational coupling : Flat, homogeneous and isotropic Universe  flat FRW metric Where :

  6. Effective potential : ; Equation of state for the background : Convergencetowards General Relativity requires that Veff has a minimum where a(j) vanishes. • Three types of models : • V(j)=0 and ∫a(j) has a minimum where a(j) vanishes. • V(j)=0 and ∫a(j) has a stationary point where a(j) vanishes. Then we need • conditions on the initial values to have convergence. • V(j) has a minimum where a(j) vanishes

  7. Three types of effective potentials leading to different convergence mechanisms : Veff(j) Veff(j) Veff(j) Radiation dominated era l grows j j j Veff(j) Matter dominated era l grows

  8. Solving the lithium problem with a scalar field When V(j)=0, the scalar field does’nt evolve during the radiation dominated era (if the initial conditions are set so that )  So, a constant value of the coupling during BBN cannot explain the lithium abundance  We need an evolving scalar field during the radiation dominated era

  9. Model defined by : With a=4 and b= 2.68 this yields : We succeeded in lowering the lithium abundance We begin slower than in General relativity and finish faster Case of a vanishing potential

  10. Model :  less efficient Case of a quartic potential The speed-up factor crosses 1 at a few MeV Temperatures of freeze-out are strongly modified

  11. a No constraint from the lithium abundance  The mechanism responsible for the decrease of the lithium abundance is very general and constrained by the temperature of freeze-out for the weak interaction processes that interconvert n and p

  12. Conclusion • We reconcile the lithium abundance with its observed value when • the baryon density is supposed high. • Purely dynamical modification. • Very general mechanism : a wide variety of models • predict the right lithium abundance. • Importance of the speed-up factor evolution : the expansion starts • slower than in General Relativity and finishes faster. • Consequences on CMB ?

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