Download Kahniashvili

Evolution and Signatures
of
Helical Magnetic Fields
Tina Kahniashvili
McWilliams Center for Cosmology
Carnegie Mellon University
&
Abastumani Astrophysical Observatory
Ilia State University
NORDITA
June 24 2015
Based On
Kahniashvili, Maravin, Lavrelashvili, Kosowsky PRD 2014
Kahniashvili, Tevzadze, Brandenburg, Neronov, PRD 2013
Tevzadze, Kisslinger, Brandenburg, Kahniashvili, ApJ 2013
Ongoing Collaboration
(papers in preparation)
Axel Brandenburg, Ruth Durrer, Victoria Merten,
Alexander Tevzadze, Tanmay Vachaspati, Winston Yin
Cosmic Magnetic Fields
Earth MF
Interstellar MF
Galaxy MF
Sun MF
How do we observe
cosmic magnetic fields?
Electromagnetic waves &
Effects induced by magnetic fields
Magnetic Helicity
Solar activity:
Sunspots
Solar flares
Coronal mass ejection
Solar wind
Magnetic helicity reflects mirror
symmetry (parity) breaking
DIFFICULT TO DETECT
cosmic rays: Kahniashvili & Vachaspati 2006
gamma-rays: Tashiro and Vachaspati 2011
Gamma Rays vs Magnetic Helicity
Tashiro and Vachaspati 2015
Tashiro, Chen, Francesc, Vachaspati 2014
Chen, Chowdhury, Francesc,
Tashiro, Vachaspati 2014
Primordial Magnetic Field
Hypothesis
F. Hoyle in Proc. “La structure et
l’evolution de l’Universe” (1958)





Inflation
Phase transitions
Supersymmetry
String Cosmology
Topological defects
Springel
Millenium simulations
Magnetogenesis

Inflation
(Turner & Widrow 1988, Ratra 1992)

• The correlation length larger
than horizon
• Scale invariant spectrum
• Well agree with the lower
bounds
 Phase Transitions
Diffuculties
(Harrisonl 1970, Vachaspati 1991)
• Backreaction
• Bubble collisions – first order
• Symmetries violation
phase transitions
 QCDPT
 EWPT
• Causal fields
• Limitation of the correlation
length
 Smoothed and effective fields
approaches
Cosmological vs. Astrophysical Magnetogenesis
MHD Simulations by Donnert et al. 2008
Ejection
Z=4
Z=0
Primordial
Z=4
Z=0
Cosmological Magnetic Fields
(Obvious Limits)

BBN limits: 10% of
additional
relativistic
component
• 0.1 – 1 microGauss
(comoving value)



Grasso and Rubistein
2000
Yamazaki and
Kusakabe 2012
Kawasaki and
Kusakabe 2012

Faraday Rotation
Measure
• At z~2-3
microGauss


Bernet et al. 2009
Kronberg et al. 2008
Magnetized CMB Perturbations
Faraday rotation does
not depend on magnetic
helicity

Density perturbations - scalar mode
• Fast and slow magnetosound waves



Adams et al. 1996
Jedamzik, Katalinic, Olinto, 1996
Vorticity perturbations - vector mode
• Alfven waves



Subramanian and Baroow, 1998
Durrer, Kahniashvili, and Yates, 1998
Gravitational waves - tensor Mode


Deryagin et al. 1986
Durrer, Ferreira, Kahniashvili 2000
Modeling Helical Magnetic Field
Kahniashvili, Kosowsky, Lavrelashvili, Maravin, 2014
Magnetic Helicity Effects on CMB
• Parity-even fluctuations
Temperature - Temperature
 Temperature - E polarization
 E-polarization – E-polarization
 B-polarization – B-polarization

• Parity-odd fluctuations
Temperature – B-polarization
 E-polarization – B-polarization

Pogosian, Vachaspati, and Winitski 2000, Caprini, Durrer, and
Kahniashvili, 2003, Kahniashvili and Ratra 2005, Kunze 2012,
Kahniashvili, et al. 2014, Balardini, Finelli, and Paoletti, 2014
Magnetic Helicity vs. WMAP 9 years data
Kahniashvili, Kosowsky, Lavrelashvili, Maravin, 2014
Magnetic Helicity Effects
Magnetic Helicity Limits
Kahniashvili, Kosowsky, Lavrelashvili, Maravin, 2014
Phenomenology

If the magnetic field has been generated
through a causal process in the early
universe it’s correlation length could not
exceed the Hubble horizon at the moment
of the generation
MHD Modeling

Coupling of the magnetic
field with primordial
plasma

Brandenburg, Kahniashvili, Tevzadze 2014
Injection of the magnetic
energy at a given scale
(phase transition bubble)
Modeling Magnetic Field
smoothed vs. effective
magnetic field
Kahniashvili, Tevzadze,
Brandenburg, Neronov 2013
one-scale (delta function)
magnetic field
Phase Transitions Generated Magnetic Field
Phenomenology


Non-helical field
Helical field
• Helicity conservation law
Kahniashvili, Tevzadze, Brandenburg, Neronov 2013
Kahniashvili, Tevzadze, Brandenburg, Neronov 2013
Magnetic field from QCD Phase Transitions
Tevzadze, Kisslinger, Brandenburg, Kahniashvili 2012
Our analysis show that in the most optimistic scenario the
magnetic correlation length in the comoving frame can
reach 10 kpc with the amplitude of the effective magnetic
field being 0.007 nG. We demonstrate that the considered
model of magneto-genesis can provide the seed magnetic
field for galaxies and clusters.
Magnetic Helicity Growth
Tevzadze, Kisslinger, Brandenburg, Kahniashvili 2012


The correlation length
should satisfy:
Fractional magnetic helicity
grows until it reaches its
maximal value
Helical Magnetic Fields Decay
Brandenburg, Kahniashvili, Tevzadze 2015
Causal fields – correlation length limitation
nB=2 or nB=0
Inverse Cascade
Helical Magnetic Fields Decay
Vachaspati 2001
Helical Magnetic Field
Brandenburg, Kahniashvili, Tevzadze 2015
Inflationary Magnetic Helicity
Magnetic field correlation length might be as large
as the Hubble horizon today or even larger
(infinity)
Can we see the imprints of an a-causal field?
Kahniashvili, Brandenburg, Durrer, Tevzadze, Yin, 2015
Inflation Generated Helical Magnetic Field
Kahniashvili, Brandenburgh, Durrer, Tevzadze, Yin 2015
The absence of inverse cascade for
Inflation generated magnetic fields
Helical Magnetic Fields
Scaling Laws
Brandenburg, Kahniashvili, Tevzadze 2015
Conclusion




The lower bound of the extragalactic magnetic field
favors a primordial magnetogenesis approach (in
particular, helical magnetic fields)
The primordial magnetic field might be a plausible
explanation for the galaxy magnetic field
Cosmological magnetic field order of 0.1 nanoGauss
can be detectable by the nearest future CMB
polarization and LSS measurements
On the other hand, if the field is significantly
smaller – it would satisfy the LOWER limit bound
but would not been observable through
cosmological observations