Konstantinos Dimopoulos

1. Where galaxies really come from Konstantinos Dimopoulos Lancaster University Contemporary Physics 50 (2009) 633-646 arXiv: 0906.0903 [hep-ph] Invited contribution to 50th Anniversary Special Edition

2. Expanding Universe: • Finite Age: • CMB Anisotropy: Hot Big Bang and Cosmic Inflation • Early Universe = Hot + Dense: CMB • On large scales:Universe = Uniform • Structure: smooth over 100 Mpc: Universe m Fractal

3. Hot Big Bang and Cosmic Inflation • Cosmological Principle:The Universe is Homogeneous and Isotropic • Incompatible with Finite Age • Horizon Problem:Uniformity over causally disconnected regions • The CMB appears correlated on superhorizon scales (in thermal equilibrium at preferred reference frame) • Cosmic Inflation:Brief period of superluminal expansion of space • Inflation produces correlations over superhorizon distances by expanding an initially causally connected region to size larger than the observable Universe

4. Primordial Density Perturbation : Hot Big Bang and Cosmic Inflation • Inflation imposes the Cosmological Principle / • Cosmological Principle =exact • Inflation + Quantum Vacuum • Sachs-Wolfe:CMB redshifted when crossing overdensities enough for structure • Inflation imposes the cosmological principle and deviations from it

5. Classical Vacuum: • Quantum Vacuum: • Uncertainty Principle: Controlled violation of Energy Conservation Classical and Quantum Vacuum • Manifests as appearance of pairs of virtual particles • Vacuum filled with virtual particles: vacuum (zero-point) energy

6. Casimir experiment • Pair of parallel conducting plates, not charged + not connected through circuit • Classically = no force • Virtual photons between plates can only have a discrete spectrum of wavelength/energy: • Virtual photons outside plates can have any wavelength/energy! • Difference (gradient) of Vacuum Energy = Force!

7. Black Hole radiates with thermal spectrum of Hawking temperature Black Hole Thermodynamics • Hawking: Black Holes + Quantum Vacuum • Black Hole:Extremely compact object with locally intense gravitational field • Event Horizon: surface within which gravity is so strong that nothing escapes • A Black Hole can shrink due to Hawking radiation • A classical Black Hole can only grow in mass and size • A tiny fraction of virtual particles can escape from the Event Horizon • Distant observer: virtual particles become real

8. Perturbations of fields aDensity Perturbation (source of structure) Density Perturbations from Inflation • Cosmic Horizon in inflation = Event Horizon of “inverted” Black Hole centred at observer • Virtual particles are pulled out of the horizon and become real • Bath of Hawking radiation fills Horizon a all space • Particle Production: Quantum fluctuations a classical perturbations • Perturbations generated during inflation asuperhorizon in size • Observational confirmation of Hawking Radiation + Inflation

9. Which fields to use? • All mechanisms that generate the density perturbation use scalar fields • Scalar fields: hypothetical spin-zero fields (one degree of freedom) • Scalar fields are ubiquitous in theories beyond the standard model such as Supersymmetry (scalar partners) or String Theory (moduli) • However,no fundamental scalar field has ever been observed • Only one fundemental scalar field in the Standard Model: the Higgs • What if the LHC does not find any scalar fields? • Designing models using unobserved scalar fields undermines their predictability and falsifiability, despite the recent precision data • Can we generate the density perturbations without scalar fields? • Use vector boson fields ! Spin-one (three degrees of freedom) • Standard Model: Photon + electroweak massive bosons: Z, W m

10. Harmonic oscillations rapidly alternate direction of Vector Field The case of Vector Fields • Inflation homogenises Vector Fields • To affect or generate the density perturbation a Vector Field needs to (nearly) dominate the Universe • However, A Homogeneous Vector Field is in general anisotropic • Basic Problem:large-scale anisotropy in conflict with uniformity of CMB • Oscillating vector field avoids excessive large-scale anisotropy with • Equation of Motion: • No net direction: Oscillating Vector Field = isotropic • Oscillating Vector Field can dominate the Universe without problem • Second Problem:Conformal invariance of massless Vector Field • Conformality: Vector Field unaffected by Universe expansion a virtual particles not pulled outside Horizon a no perturbations • Explicit breaking of conformality required (model dependent)

11. l=5 in preferred frame Distinct observational signatures • Oscillation of Vector Field = not exactly harmonic: Amplitude decreases due to expansion l=5 in galactic coordinates • a Weak large-scale anisotropy • Might be present in CMB (“Axis of Evil” observation): • Anisotropic particle production:due to three degrees of freedom • a Statistical Anisotropy New observable! • Anisotropic patterns in the CMB • Weak upper bound only: < 30% • Observable by Planck satellite : (bound < 2%)

12. The majority of galaxies carry magnetic fields of equipartition value: • Dynamo can amplify magnetic fields up to equipartition value but needs weak seed field to feed on: Density perturbations and magnetic fields • In spirals the magnetic fields follow spiral arms agalactic dynamo • Origin of seed field remains elusive • Suppose Hypercharge obtains in inflation a superhorizon spectrum of perturbations • At electroweak transition Hypercharge is projected onto photon and Z-boson • If Z-boson a perturbations then photona magnetic field enough to seed dynamo • Correlation of overdensities and magnetic field intensity assists structure formation

13. Summary & Conclusions • All structures in the Universe originated from quantum fluctuations • Quantum fluctuations are stretched to superhorizon sizes and become classical perturbations, during a period of cosmic inflation • Cosmic inflation is a brief period of superluminal expansion of space • Inflation forces uniformity onto the Universe and deviations from it • Recent CMB observations have confirmed both inflation and the Hawking radiation process. This is the earliest data at hand • The precision of cosmological observations has reached the level which demands model-building to become detailed and rigorous • In light of forthcoming LHC findings it may be necessary to explore alternatives beyond scalar fields such as vector fields or spinors • Massive vector fields can generate the density perturbation without excessive large scale anisotropy if they oscillate before domination • New observables: weak large-scale anisotropy (“Axis of Evil”) and statistical anisotropy (direction dependent patterns) - up to 30% • Use of Y-boson correlates structure formation with galactic magnetism

14. Publications Phys.Rev.D83:023523,2011 Phys.Lett.B683:298-301,2010 Phys.Rev.D81:023522,2010 Phys.Rev.D80:023509,2009 JCAP 0905:013,2009 JHEP 0807:119,2008 Phys.Rev.D76:063506,2007 Phys.Rev.D74:083502,2006