Konstantinos Dimopoulos Lancaster University Contemporary Physics 50 (2009) arXiv: [hep-ph] Invited contribution to 50 th Anniversary Special Edition

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

Hot Big Bang and Cosmic Inflation Cosmological Principle: The Universe is Homogeneous and Isotropic Horizon Problem: Uniformity over causally disconnected regions 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 The CMB appears correlated on superhorizon scales (in thermal equilibrium at (in thermal equilibrium at preferred reference frame) preferred reference frame)  Incompatible with Finite Age

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

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

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!

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

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 Particle Production: Quantum fluctuations  classical perturbations Bath of Hawking radiation fills Horizon  all space Perturbations generated during inflation  superhorizon in size Observational confirmation of Hawking Radiation + Inflation Perturbations of fields  Density Perturbation (source of structure)

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

The case of Vector Fields Basic Problem: large-scale anisotropy in conflict with uniformity of CMB Oscillating vector field avoids excessive large-scale anisotropy Inflation homogenises Vector Fields To affect or generate the density perturbation a Vector Field needs to (nearly) dominate the Universe However However, A Homogeneous Vector Field is in general anisotropic 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  virtual particles not pulled outside Horizon  no perturbations Explicit breaking of conformality required (model dependent) Equation of Motion: Harmonic oscillations rapidly alternate direction of Vector Fieldwith

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

Density perturbations and magnetic fields In spirals the magnetic fields follow spiral arms  galactic 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  perturbations then photon  magnetic field enough to seed dynamo Correlation of overdensities and magnetic field intensity assists structure formation Dynamo can amplify magnetic fields up to equipartition value but needs weak seed field to feed on: The majority of galaxies carry magnetic fields of equipartition value:

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 Inflation forces uniformity onto the Universe and deviations from it Cosmic inflation is a brief period of superluminal expansion of space 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

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