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L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina Open page

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Cosmological Tests of the Cosmological Constant Λ The Cosmological Constant (w=-1) remains consistent with all current data as a driving force of the acceleration. Geometrical (Standard Candles, Standard Rulers) Dynamical (Growth of Fluctuations by Gravity) Q: What could be the origin of Λ? Α: Vacuum Fluctuations with Cutoff (ω c =10 -3 eV, l c =0.1mm) Cutoff Prediction: Change of sign of Casimir Force ( ) Extra Dimension: Change of sign at higher separations Q: What Experiment could probe the cutoff structure of the vacuum in the lab? A: Casimir Effect (detected attraction of metal plates)

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Predicted Hubble Expansion History (flat universe): Luminosity Distance (standard candles - SnIa): SnIa Obs Angular Diameter Distance (standard rulers – CMB sound horizon):

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Generalize H(z): Minimize: Standard Candles (SnIa) Standard Rulers (CMB+BAO) Lazkoz, Nesseris, LP arxiv: 0712.1232 2σ tension between standard candles and standard rulers ESSENCE+SNLS+HST data WMAP3+SDSS(2007) data

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Measure growth function of cosmological perturbations: Parametrization: Predicted Evolution of δ : (General Relativity) Wang, Steinhardt, Astrophys.J.508:483-490,1998

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Parametrization:

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Fit to LSS data: ΛCDM provides an excellent fit to the linear perturbations growth data S. Nesseris, LP, arxiv: 0710.1092, Phys.Rev.D77:023504,2008 best fit ΛCDM

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Equivalence Principle Gravity couples to the zero point energy of the vacuum Q: Can we probe the zero point energy of the vacuum in the lab? A: No! Non-gravitational experiments are only sensitive to changes of the zero point energy. But: This is not so in the presence of a physical finite cutoff ! Casimir Force Experiments can pick up the presence of a physical cutoff !! EM field zero point vacuum energy: Majajan, Sarkar, Padmanbhan, Phys.Lett.B641:6-10,2006

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Vacuum Energy gets modified in the presence of the plates (boundary conditions) Attractive Force Harris, Chen, Mohideen, 2000 Agreement between theory and experiment at 1%

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EM vacuum energy with cutoff UV regulator Modification of vacuum energy due to the plates:

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attractive repulsive β=0 (R=0) β=1 β=0 (R=0) Thus, the cutoff predicts a Casimir force which becomes repulsive for d<0.6mm (not consistent with experiments) LP, arxiv: 0802.1531, accepted in Phys.Rev.D (to appear)

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Poppenhaeger et. al. hep-th/0309066 Phys.Lett.B582:1-5,2004 Casimir Force decreases in the presence of an extra dimension

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A change of sign of the Casimir force at low surface separations could be an indication of a fundamental cutoff in the vacuum energy modes. Such a cutoff could be an indication of both new physics and the origin of the Cosmological Constant. β=1 β=0 (R=0)

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Standard Rulers are systematically less in favor of ΛCDM than Standard Candles.

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Cosmological Tests of the Cosmological Constant Λ The Cosmological Constant (w=-1) remains consistent with all current data as a driving force of the acceleration. Geometrical (Standard Candles, Standard Rulers) Dynamical (Growth of Fluctuations by Gravity) Q: What could be the origin of Λ? Α: Vacuum Fluctuations with Cutoff (ω c =10 -3 eV, l c =0.1mm) Cutoff Prediction: Change of sign of Casimir Force (d

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