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