Cosmic Strings: Theory and Observations

1
Cosmic Strings Theory and Observations

• Olga S. Khovanskaya
• (Sternberg Astronomical Institute, Moscow,
  Russia)

16 November 2004, Dipartimento di Scienze
Fisiche, Univ. Federico II, Polo delle Scienze a
della tecnologia, via Cinthia, 80126 Napoli,
Italy
2
RELICT (Strukov I.A. et al. MNRAS 258 37P
1992) COBE (Smoot G.F. et al. Astrophys. J. 396
L1 1992) BOOMERanG (de Bernardis P. et al.
Nature 404 955 2000) Archeops WMAP (Wilkinson
Microwave Anisotropy Probe, http//map.gsfc.nasa.g
ov)
Current data of microwave background measurements
exclude cosmic strings and other topological
defects as primary source of primordial density
perturbations.
3
Our Universe has several mysterious properties
which are not fitted with generally accepted
standard cosmological model. Most well known
are 1. The low multipole anisotropy is too
small 2. First Doppler peak has double peak
structure which does not be explained within
standard cosmological model 3. The correlation
function of galaxies are fitted with broken
power-law empirical fit instead of standard
power law fit.
One of the possible explanation is that dark
matter has complex structure and consists from
different type of matter which change both
spectrum of primordial fluctuation and transfer
function. Cosmic string is one of possible
candidate for such type.
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?
fundamental strings of superstring theory
cosmic strings
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?
fundamental strings of superstring theory
cosmic strings
The energy scale for cosmic strings is the
scale of GUT or less
The energy scale for fundamental strings is
Planck scale
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?
fundamental strings of superstring theory
cosmic strings
Such heavy strings do not exist in our Universe
today, and cannot have played any role in
cosmological evolution except in the first few
Planck times
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It was found deep relation between macroscopic
cosmic strings and microscopic fundamental
strings.
fundamental strings of superstring theory
cosmic strings
Now we know models with large compact
dimensions, in which the string scale may be
much lower, down to the GUT scale or even less.
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Branes, which now play key role in superstring
theory, can collide and generate cosmic strings.
In modern brane cosmology the string production
is natural in contrast to monopoles and domain
wools production.
A
Brane A
B
Brane B
only strings no monopoles no domain wools
String theory now provides a much richer family
of branes with different properties. For this
reason, if we could discover what kind of cosmic
stings exist in our Universe it would tell us a
lot about the underlying fundamental theory.
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Cosmic string in the Universe
Bubble nucleations
The Universe cooled
The very hot Universe is in Symmetric phase. No
strings.
The Hidds field tends to settle down into the
valley
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Cosmic string in the Universe
Euclidean Universe
Euclidean Universe
1
2
Euclidean Universe
B
B
A
Conical Universe
A
3
4
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Cosmic string as gravitational lens schematic
model of formation of two images of background
source
Euclidean Universe
Euclidean Universe
B
2
1
2
A
If the angular distance between the background
source and the string is less than the
observer sees two images separated by angle
3
B
Conical Universe
A
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Cosmic string as gravitational lens "milky way"
of lensed background sources
- deficit angle
- string density,
- angle between the string and the vector
coinciding with the observer and the point
source
- angular cosmological distance from the
observer to the string
- angular cosmological distance between the
background source and the observer
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CSL1 double source
Distance from solar system to CSL-1 is 1900 Mpc
(for Hubble constant H65 km/s)
CSL-1 coordinates (2000)
CSL-1 chance projection effect or serendipitous
discovery of a gravitational lens induced by a
cosmic string? Sazhin M., Longo G., Capaccioli M.
et al. MNRAS 343, 353 (2003).
Lens candidates in the Capodimonte Deep Field in
vicinity of the CSL-1 object, Sazhin M.,
Khovanskaya O., Capaccioli M. et al.
astro-ph/0406516
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The chance aligment of two galaxies
1. Gravitational tidal interaction of the galaxy
pair
2. Gravitational lensing of the galaxy pair on
each other
CSL-1 as result of gravitational effects
1. Gravitational lensing of the background galaxy
on standard object
2. The first observation of gravitational
lensing of the background galaxy on cosmic string
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The chance aligment of two galaxies
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The chance aligment of two galaxies
1. Gravitational tidal interaction of the galaxy
pair
no distortions no interaction
visual distance
1
2
physical distance
distortions defined by fotometric accuracy
1
2
2. Gravitational lensing of the galaxy pair on
each other
1
1
2
2
observer
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500 km/s
The chance aligment of two galaxies
600 km/s
700 km/s
400 km/s
A
B
10 photometric accuracy (now available in OAC DF)
300 km/s
0.1
200 km/s
100 km/s
1 photometric accuracy
0.01
0.1 photometric accuracy
Relative distortion
0.001
0.0001
10
100
1000
10000
100000
Distance between the galaxies in units of galaxy
radius
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Future experiment
400 km/s
10 photometric accuracy (now available in OAC DF)
0.1
1 photometric accuracy
0.01
All black region is the region to define the
typical distortion by tidal effects and by
gravitational lensing of one galaxy by the other
0.1 photometric accuracy
Relative distortion
0.001
0.0001
10
100
1000
10000
100000
Distance between the galaxies in units of galaxy
radius
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CSL-1 as result of gravitational effects
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CSL-1 as result of gravitational effects
0.8452
The probability that there are two different
spectra with the correlation coefficient 0.8452
for 1000 point is very small
400 km/s
Correlation coefficient of NTT spectra with
background removed
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CSL-1 as result of gravitational effects
observed profiles in all available band
A
B
Dust?
915 nm 837 nm 815 nm 791 nm 770 nm 753 nm R V B
A
B
Dust?
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CSL-1 as result of gravitational effects
914 nm
753 nm
B - filter
R - filter
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CSL-1 as result of gravitational effects
Optimal SIS lens (914 nm)
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CSL-1 as result of gravitational effects
Residuals ("modelled-observed") for SIS lens
model (914 nm)
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CSL-1 as result of gravitational effects
Residuals ("modelled-observed") for string lens
model (914 nm)
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Future experiment (1)
Surface brightness contours of the light
distribution resulting from the model of lensing
of a de Vaucouleur spheroid by a cosmic string
Contours of simulated image for pixel size 0.05
arcsec and with noise
Contours of simulated image after rebinning to
the OAC DF pixel size (0.238 arcsec) and
convolving with the observed OAC DF PSF (0.98
arcsec)
We need to achieve an angular resolution better
than 0.1 arcsec
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CSL-1 as result of gravitational effects
CSL-1
To give additional proof to cosmic string
scenario we have to find the discussed above new
milky way of galaxies

• Necessary (but not sufficient!) conditions to
  select gravitational lens candidates in vicinity
  of CSL-1
• One or more images with small angular separation
  (1-4.5)
• The same flux ratio in different band

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CSL-1 as result of gravitational effects
N
In the case of lensing by a string we expect a
number of lenses from 9 (straight string) up to
200 (curved string). According to the usual
gravitational lens statistic there have to be
only 2 lenses in the field.
Each point represents the pair
3
9
6
E
11
7
CSL-1
5
1
8
4
16 x 16
10
2
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CSL-1 as result of gravitational effects
To receive the sufficient condition that our
candidates have gravitational nature we need
their spectra to be identical
CSL-1
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CSL-1 as result of gravitational effects
?
CSL-1
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Future experiment (2)
We have not received spectra on VLT! The weather
was bad!
We need to obtain the spectra for both components
of each lens candidate in order to assess whether
their redshift and overall spectral morphologies
confirm or disprove their gravitational lens
nature. If a significant excess of gravitational
lenses will be found this would strongly indicate
that CSL-1 is result of gravitational lensing by
a cosmic string.
CSL-1
Usual gravitational lenses
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Conclusions
If we accept the interpretation of CSL-1 as
gravitational lens produced by a cosmic string,
it is possible to derive the scale of energy at
which the symmetry breaking occurred.
The distance between the peaks of the two images
2 of CSL-1 roughly corresponds to the
deficit angle. One can therefore estimate the
density of the string as
and the mass scale of symmetry breaking as