1. Evolution and Signatures of Helical Magnetic Fields
Tina Kahniashvili
McWilliams Center for Cosmology Carnegie Mellon University
&
Abastumani Astrophysical Observatory
Ilia State University
NORDITA
June
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2. Ongoing Collaboration (papers in preparation)
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

3. Cosmic Magnetic Fields
Earth MF
Interstellar MF
Galaxy MF
Sun MF

4. Electromagnetic waves & Effects induced by magnetic fields
How do we observe
cosmic magnetic fields?
Electromagnetic waves &
Effects induced by magnetic fields

5. 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

6. Gamma Rays vs Magnetic Helicity
Tashiro and Vachaspati 2015
Tashiro, Chen, Francesc, Vachaspati 2014
Chen, Chowdhury, Francesc, Tashiro, Vachaspati 2014

7. 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

8. Magnetogenesis Inflation The correlation length larger than horizon
(Turner & Widrow 1988, Ratra 1992)
The correlation length larger than horizon
Scale invariant spectrum
Well agree with the lower bounds
Diffuculties
Backreaction
Symmetries violation
Phase Transitions
(Harrisonl 1970, Vachaspati 1991)
Bubble collisions – first order phase transitions
QCDPT
EWPT
Causal fields
Limitation of the correlation length
Smoothed and effective fields approaches

9. Cosmological vs. Astrophysical Magnetogenesis MHD Simulations by Donnert et al. 2008
Ejection Primordial
Z=4
Z=4
Z=0
Z=0

10. 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

11. 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

12. Modeling Helical Magnetic Field
Kahniashvili, Kosowsky, Lavrelashvili, Maravin, 2014

13. 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

14. Magnetic Helicity vs. WMAP 9 years data
Kahniashvili, Kosowsky, Lavrelashvili, Maravin, 2014

15. Magnetic Helicity Effects

16. Magnetic Helicity Limits
Kahniashvili, Kosowsky, Lavrelashvili, Maravin, 2014

17. 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

18. MHD Modeling Coupling of the magnetic field with primordial plasma
Injection of the magnetic energy at a given scale (phase transition bubble)
Brandenburg, Kahniashvili, Tevzadze 2014

19. Modeling Magnetic Field
one-scale (delta function)
magnetic field
smoothed vs. effective magnetic field
Kahniashvili, Tevzadze, Brandenburg, Neronov 2013

20. Phase Transitions Generated Magnetic Field Phenomenology
Non-helical field
Helical field
Helicity conservation law

21. Kahniashvili, Tevzadze, Brandenburg, Neronov 2013

22. Kahniashvili, Tevzadze, Brandenburg, Neronov 2013

23. 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 nG. We demonstrate that the considered model of magneto-genesis can provide the seed magnetic field for galaxies and clusters.

24. Magnetic Helicity Growth
Tevzadze, Kisslinger, Brandenburg, Kahniashvili 2012
The correlation length should satisfy:
Fractional magnetic helicity grows until it reaches its maximal value

25. Helical Magnetic Fields Decay
Brandenburg, Kahniashvili, Tevzadze 2015
Causal fields – correlation length limitation
nB=2 or nB=0
Inverse Cascade

26. Helical Magnetic Fields Decay
Vachaspati 2001

27. Helical Magnetic Field
Brandenburg, Kahniashvili, Tevzadze 2015

28. 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

29. Inflation Generated Helical Magnetic Field
Kahniashvili, Brandenburgh, Durrer, Tevzadze, Yin 2015
The absence of inverse cascade for
Inflation generated magnetic fields

30. Helical Magnetic Fields Scaling Laws
Brandenburg, Kahniashvili, Tevzadze 2015

31. 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

32. Thank You