L. Perivolaropoulos Department of Physics University of Ioannina Open page

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)

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

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

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

Parametrization:

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

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

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%

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

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: , accepted in Phys.Rev.D (to appear)

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

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)

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

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<l c ) : Not Detected 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) Unless New Physics is imposed, current Casimir force experiments are not consistent with the presence of the cutoff required to produce the observed value of Λ.