konstantinos dimopoulos lancaster university contemporary physics 50 (2009) 633-646 arxiv: 0906.0903...
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Konstantinos Dimopoulos
Lancaster University
Contemporary Physics 50 (2009) 633-646Contemporary Physics 50 (2009) 633-646
arXiv: 0906.0903 [hep-ph]arXiv: 0906.0903 [hep-ph]
Invited contribution to 50th Anniversary Special EditionInvited contribution to 50th Anniversary Special Edition
Hot Big Bang and Cosmic InflationHot Big Bang and Cosmic Inflation
Expanding Universe:Expanding Universe:
Early Universe = Hot + Dense: Early Universe = Hot + Dense: CMB
Finite Age:Finite Age:
On large scales:On large scales: Universe = Uniform
Structure: smooth Structure: smooth over 100 Mpc: over 100 Mpc: Universe Fractal
CMB Anisotropy:CMB Anisotropy:
Hot Big Bang and Cosmic InflationHot 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 Inflation produces correlations over superhorizon distances by over superhorizon distances by expanding an initially causally expanding an initially causally connected region to size larger connected region to size larger than the observable Universethan 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 AgeIncompatible with Finite Age
Hot Big Bang and Cosmic InflationHot 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 structureenough for structure
Sachs-Wolfe:Sachs-Wolfe: CMB redshifted when crossing overdensities
Primordial Density Primordial Density Perturbation :Perturbation :
/
Classical and Quantum VacuumClassical 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 experimentCasimir 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 ThermodynamicsBlack 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 InflationDensity 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?Which fields to use?
Scalar fields are ubiquitous in theories beyond the standard model such as Supersymmetry (scalar partners) or String Theory (moduli)
HoweverHowever, 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 FieldsThe 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
HoweverHowever, 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
Field
withwith
Distinct observational signaturesDistinct 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 fieldsDensity 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 & ConclusionsSummary & 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
PublicationsPublications
JCAP 0905:013,2009JCAP 0905:013,2009
JHEP 0807:119,2008JHEP 0807:119,2008
Phys.Rev.D83:023523,2011 Phys.Rev.D83:023523,2011
Phys.Rev.D76:063506,2007 Phys.Rev.D76:063506,2007
Phys.Rev.D74:083502,2006 Phys.Rev.D74:083502,2006
Phys.Lett.B683:298-301,2010Phys.Lett.B683:298-301,2010
Phys.Rev.D80:023509,2009Phys.Rev.D80:023509,2009
Phys.Rev.D81:023522,2010Phys.Rev.D81:023522,2010