1 / 21

210 likes | 393 Vues

Open page. A Comparison of. Dark Energy Probes. L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina. Structure of Talk. Introduction - Key Questions - Latest Data. Geometric Constraints: Standard Rulers vs Standard Candles.

Télécharger la présentation
## L. Perivolaropoulos leandros.physics.uoi.gr Department of Physics University of Ioannina

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**Open page**A Comparison of Dark Energy Probes L. Perivolaropouloshttp://leandros.physics.uoi.gr Department of Physics University of Ioannina**Structure of Talk**Introduction - Key Questions - Latest Data Geometric Constraints: Standard Rulers vs Standard Candles Gamma Ray Bursts as Standard Candles Current Dynamical Constraints: Growth Rate from Redshift DistortionWeak Lensing Potential Constraints from Laboratory Experiments: Signatures of a cutoff in the Casimir Effect Conclusions**Candidate Model Classes**Cosmological Constant Expansion History Gmn- L gmn = k Tmn Dark Energy Gmn = k (Tmmn+ T’μν) Allowed Sector Eq. of state evolution Forbidden(ghosts) Modified Gravity G’mn = k Tmmn Allowed Sector**Key Questions**Is General Relativity the correct theory on cosmological scales? What is the most probable form of w(z) and what forms of w(z) can be excluded? Is ΛCDM (GR + Λ) consistent with all cosmological observations? What is the recent progress?**Accelerating Expansion: Latest Constraints**Latest data (307 SnIa)Kowalski et. al. arXiv:0804.4142 Recent dataWood Vasey et. al. astro-ph/0701041 4 years agoRiess et. al. astro-ph/0402512Astrophys.J.607:665-687,2004 Chevallier-Polarski, Linder**Accelerating Expansion: Latest Constraints**4 years agoRiess et. al. astro-ph/0402512Astrophys.J.607:665-687,2004 Latest data (307 SnIa)Kowalski et. al. arXiv:0804.4142**Progress Report**Is ΛCDM (GR + Λ) consistent with all cosmological observations? Yes! Flat, ΛCDM remains at 1σ distance from the best fit since 2004. The 1σ parameter contour areas remain about the same since 2004 despite of the double size of the SnIa sample and ΛCDM remains at the lower right part of the (w0,wa) contour! Q: Which Dark Energy Probe has the weakest consistency with ΛCDM?**SnIa**Obs GRB Direct Probes of the Cosmic Metric: Geometric Observational Probes Direct Probes of H(z): Luminosity Distance (standard candles: SnIa,GRB): flat Significantly less accurate probesS. Basilakos, LP, arXiv:0805.0875 Angular Diameter Distance (standard rulers: CMB sound horizon, clusters):**Geometric Constraints**Parametrize H(z): Minimize: WMAP3+SDSS(2007) data ESSENCE+SNLS+HST data Standard Candles (SnIa) Lazkoz, Nesseris, LPJCAP 0807:012,2008.arxiv: 0712.1232 2σ tension between standard candles and standard rulers Standard Rulers (CMB+BAO)**Gamma Ray Bursts**Gamma-ray bursts (GRBs): The most luminus electromagnetic events (1052 ergs~mass of Sun) occurring in the universe since the Big Bang Collimated emissions (0.1-100 seconds long) caused either by the collapse of the core of a rapidly rotating, high-mass star into a black holes or from merging binary systems (short bursts). GRBs are extragalactic events, observable to the limits of the visible universe; a typical GRB has a z > 1.0 while the most distant known (GRB080913) has z=6.7 Swift Satellite (2004) Shells of energy and matter ejected by the newly-formed hole collide and merge ("internal shocks"). The shell sweeps up more and more material it slows down and releases energy (afterglow).**GRB Correlations**GRBs are not standard candles but may be calibrated using empirical correlation relations between energy output and lightcurve measurable observables. Example of Correlation: Steps for cosmological fitting (Schaefer astro-ph/0612285, Hong Li et. al. Phys.Lett.B658:95-100,2008) : 1. Assume Schaefer astro-ph/0612285 or and fit for a, b using a specific cosmological model to find Li 2. Use the fitted a, b to find the ‘correct’ Li from the observed Epeak i L obtained from 3. Use the new Li , along with li, zi to fit cosmological parameters Circularirty problem: A cosmological model has been used to calibrate a, b !!**Fixing the Circularity Problem**S. Basilakos, LP, arXiv:0805.0875,accepted in MNRAS (to appear) Fit a, b along with the cosmological parameters (eg Ωm): Minimize χ2 wrt a, b, Ωm:**GRB vs Other Probes**Current GRB data are not competitive with other geometric probes. The calibration has too much scatter and there are additional parameters to be fit.**Dynamical Probes I: Redshift Distortion**The power spectrum at a given redshift is affected by systematic differences between redshift space and real space measurements due to the peculiar velocities of galaxies. Galaxy power spectrum in redshift space Galaxy power spectrum in real space space μ=cosθand θis the angle between and the lineof sight. Find f Measure β**Dynamical Constraints**Measure growth function of cosmological perturbations: Evolution of δ : Parametrization: Fit to LSS data: ΛCDM ΛCDM provides an excellent fit to the linear perturbations growth data best fit S. Nesseris, LP, Phys.Rev.D77:023504,2008**Dynamical Probes II: Weak Lensing**L. Fu et al.: Very weak lensing in the CFHTLS Wide, arxiv. 0712.0884 Use weak lensing to observe the projected dark matter power spectrum (cosmic shear spectrum) and compare with ΛCDM predictions using maximum likelihood.**Growth and the CMB Shift Parameter**Flat models 1, 2, 3 have identical shift parameter R and Ωm but different H(z). The growth function D(a) in the context of G.R. is mainly determined by the shift parameter R and Ωm . This may be used as a test of G.R. S. Nesseris, LP, JCAP 0701:018,2007 S. Basilakos, S. Nesseris, LP, Mon.Not.Roy.Astron.Soc.387:1126-1130,2008.**Quantum Vacuum: Simplest Origin of Cosmological Constant**Quantum Vacuum is not empty! Sea of virtual particles Whose existence has been detected (eg shift of atomic levels in H) W. Lamb, Nobel Prize 1955 Quantum Vacuum is elastic (p=-ρ) ΔV 1st law F same as Λ Quantum Vacuum is Repulsive (ρ+3p=-2ρ) Quantum Vacuum is divergent! Vacuum Energy of a Scalar Field: cutoff**Zero Point Energy of Vacuum and Lab Experiments**Q: Can we probe a diverging 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 ! Majajan, Sarkar, Padmanbhan, Phys.Lett.B641:6-10,2006 Casimir Force Experiments can pick up the presence of a physical cutoff !! Vacuum Energy gets modified in the presence of the plates (boundary conditions) Attractive Force Density of Modes (relative to continuum) decreases**The Experimental Effects of a Cutoff**Cutoff: EM vacuum energy with cutoff (allow for compact extra dimension): Density of Modes is Constant.Energy of Each Mode Increases.Force becomes repulsive! Required Cutoff: With Cutoff Compact Extra dim, No cutoff LP, Phys. Rev. D 77, 107301 (2008) No extra dim. Poppenhaeger et. al.hep-th/0309066 Phys.Lett.B582:1-5,2004 with compact extra dim The cutoff predicts a Casimir force which becomes repulsive for d<0.6mm**SUMMARY**After the ‘Golden Age’ 1998-2005 of new dark energy observational constraints, the improvement of these constraints has slowed down. The most probable probe that may lead to disfavor of ΛCDM in the next few years appears to be observations of Baryon Acoustic Oscillations Laboratory Experiments related to Casimir effect have the potential to reveal useful signatures of a physical cutoff associated with vacuum energy . ‘dark energy’ ‘cmb’ No. of papers with words ‘dark energy’ and ‘CMB’ in title per year (from spires database http://www-spires.dur.ac.uk/spires/hep/

More Related