New Observational Windows to Probe Fundamental Physics

Transcription

1 1 / 46 String String New Observational Windows to Probe Fundamental Physics Searching for String Signals Robert Brandenberger McGill University May 23, 2012

2 2 / 46 Outline 1 String String 2 String 3 String 4 5 6

3 3 / 46 Plan 1 String String 2 String 3 String 4 5 6

4 T. Kibble, J. Phys. A 9, 1387 (1976); Y. B. Zeldovich, Mon. Not. Roy. Astron. Soc. 192, 663 (1980); A. Vilenkin, Phys. Rev. Lett. 46, 1169 (1981). 4 / 46 String String string = linear topological defect in a quantum field theory. 1st analog: line defect in a crystal 2nd analog: vortex line in superfluid or superconductor string = line of trapped energy density in a quantum field theory. Trapped energy density gravitational effects on space-time important in cosmology.

5 5 / 46 Relevance to Particle Physics and Cosmology I String String strings are predicted in many particle physics models beyond the Standard Model". strings are predicted to form at the end of inflation in many inflationary models. strings may survive as cosmic superstrings in alternatives to inflation such as string gas cosmology. In models which admit cosmic strings, cosmic strings inevitably form in the early universe and persist to the present time. It would be nice to see a cosmic string in the universe!

6 5 / 46 Relevance to Particle Physics and Cosmology I String String strings are predicted in many particle physics models beyond the Standard Model". strings are predicted to form at the end of inflation in many inflationary models. strings may survive as cosmic superstrings in alternatives to inflation such as string gas cosmology. In models which admit cosmic strings, cosmic strings inevitably form in the early universe and persist to the present time. It would be nice to see a cosmic string in the universe!

7 Relevance to Particle Physics and Cosmology II String String strings are characterized by their tension µ which is associated with the energy scale η at which the strings form (µ η 2 ). Searching for the signatures of cosmic strings is a tool to probe physics beyond the Standard Model at energy ranges complementary to those probed by the LHC. strings are constrained from cosmology: strings with a tension which exceed the value Gµ are in conflict with the observed acoustic oscillations in the angular power spectrum (Dvorkin, Hu and Wyman, 2011). Existing upper bound on the string tension rules out large classes of particle physics models. It is interesting to find ways to possibly lower the bounds on the string tension. 6 / 46

8 Relevance to Particle Physics and Cosmology II String String strings are characterized by their tension µ which is associated with the energy scale η at which the strings form (µ η 2 ). Searching for the signatures of cosmic strings is a tool to probe physics beyond the Standard Model at energy ranges complementary to those probed by the LHC. strings are constrained from cosmology: strings with a tension which exceed the value Gµ are in conflict with the observed acoustic oscillations in the angular power spectrum (Dvorkin, Hu and Wyman, 2011). Existing upper bound on the string tension rules out large classes of particle physics models. It is interesting to find ways to possibly lower the bounds on the string tension. 6 / 46

9 Relevance to Particle Physics and Cosmology III 7 / 46 String String strings can produce many good things for cosmology: String-induced mechanism of baryogenesis (R.B., A-C. Davis and M. Hindmarsh, 1991). Explanation for the origin of primordial magnetic fields which are coherent on galactic scales (X.Zhang and R.B. (1999). Explanation for cosmic ray anomalies (R.B., Y. Cai, W. Xue and X. Zhang (2009). Origin of supermassive black holes (R.B., in prep..). It is interesting to find evidence for the possible existence of cosmic strings.

10 Relevance to Particle Physics and Cosmology III 7 / 46 String String strings can produce many good things for cosmology: String-induced mechanism of baryogenesis (R.B., A-C. Davis and M. Hindmarsh, 1991). Explanation for the origin of primordial magnetic fields which are coherent on galactic scales (X.Zhang and R.B. (1999). Explanation for cosmic ray anomalies (R.B., Y. Cai, W. Xue and X. Zhang (2009). Origin of supermassive black holes (R.B., in prep..). It is interesting to find evidence for the possible existence of cosmic strings.

11 8 / 46 Preview String String Important lessons from this talk: strings nonlinearities already at high redshifts. cosmic strings more pronounced at high redshifts. strings lead to perturbations which are non-gaussian. strings predict specific geometrical patterns in position space. 21 cm surveys provide an ideal arena to look for cosmic strings (R.B., R. Danos, O. Hernandez and G. Holder, 2010).

12 9 / 46 Plan 1 String String 2 String 3 String 4 5 6

13 String I A. Vilenkin and E. Shellard, and other Topological Defects (Cambridge Univ. Press, Cambridge, 1994). 10 / 46 String String strings form after symmetry breaking phase transitions. Prototypical example: Complex scalar field φ with Mexican hat" potential: V (φ) = λ ( φ 2 η 2) 2 4 Vacuum manifold M: set up field values which minimize V. At high temperature: φ = 0. At low temperature: φ = η - but by causality the phase on scales larger than the horizon is uncorrelated. There are lines where φ = 0: narrow tubes of trapped potential energy: cosmic strings. Mass per unit length µ η 2 (independent of λ).

14 String I A. Vilenkin and E. Shellard, and other Topological Defects (Cambridge Univ. Press, Cambridge, 1994). 10 / 46 String String strings form after symmetry breaking phase transitions. Prototypical example: Complex scalar field φ with Mexican hat" potential: V (φ) = λ ( φ 2 η 2) 2 4 Vacuum manifold M: set up field values which minimize V. At high temperature: φ = 0. At low temperature: φ = η - but by causality the phase on scales larger than the horizon is uncorrelated. There are lines where φ = 0: narrow tubes of trapped potential energy: cosmic strings. Mass per unit length µ η 2 (independent of λ).

15 String I A. Vilenkin and E. Shellard, and other Topological Defects (Cambridge Univ. Press, Cambridge, 1994). 10 / 46 String String strings form after symmetry breaking phase transitions. Prototypical example: Complex scalar field φ with Mexican hat" potential: V (φ) = λ ( φ 2 η 2) 2 4 Vacuum manifold M: set up field values which minimize V. At high temperature: φ = 0. At low temperature: φ = η - but by causality the phase on scales larger than the horizon is uncorrelated. There are lines where φ = 0: narrow tubes of trapped potential energy: cosmic strings. Mass per unit length µ η 2 (independent of λ).

16 String I A. Vilenkin and E. Shellard, and other Topological Defects (Cambridge Univ. Press, Cambridge, 1994). 10 / 46 String String strings form after symmetry breaking phase transitions. Prototypical example: Complex scalar field φ with Mexican hat" potential: V (φ) = λ ( φ 2 η 2) 2 4 Vacuum manifold M: set up field values which minimize V. At high temperature: φ = 0. At low temperature: φ = η - but by causality the phase on scales larger than the horizon is uncorrelated. There are lines where φ = 0: narrow tubes of trapped potential energy: cosmic strings. Mass per unit length µ η 2 (independent of λ).

17 11 / 46 Formation of T. Kibble, Phys. Rept. 67, 183 (1980). String String By causality, the values of φ in M cannot be correlated on scales larger than t. Hence, there is a probability O(1) that there is a string passing through a surface of side length t. Causality network of cosmic strings persists at all times.

18 11 / 46 Formation of T. Kibble, Phys. Rept. 67, 183 (1980). String String By causality, the values of φ in M cannot be correlated on scales larger than t. Hence, there is a probability O(1) that there is a string passing through a surface of side length t. Causality network of cosmic strings persists at all times.

19 12 / 46 Scaling Solution I String Correlation length ξ(t) < t for all times t > t c. Dynamics of ξ(t) is governed by a Boltzmann equation which describes the transfer of energy from long strings to string loops String

20 Scaling Solution II String String Analysis of the Boltzmann equation shows that ξ(t) t for all t > t c : If ξ(t) << t then rapid loop production and ξ(t)/t increases. If ξ(t) >> t then no loop production and ξ(t)/t decreases. Sketch of the scaling solution: 13 / 46

21 14 / 46 History I String String strings were popular in the 1980 s as an alternative to inflation for producing a scale-invariant spectrum of cosmological perturbations. strings lead to incoherent and active fluctuations (rather than coherent and passive like in inflation). Reason: strings on super-hubble scales are entropy fluctuations which seed an adiabatic mode which is growing until Hubble radius crossing. Boomerang data (1999) on the acoustic oscillations in the angular power spectrum ruled out cosmic strings as the main source of fluctuations.. Interest in cosmic strings collapsed.

22 History II String String Supergravity models of inflation typically yield cosmic strings after reheating (R. Jeannerot et al., 2003). Brane inflation models typically yield cosmic strings in the form of cosmic superstrings (Sarangi and Tye, 2002; Copeland, Myers and Polchinski, 2004). String Gas Cosmology may lead to a remnant scaling network of cosmic superstrings (R.B. and C. Vafa, 1989: A. Nayeri, R.B. and C. Vafa, 2006). renewed interest in cosmic strings as supplementary source of fluctuations. Best current limit from angular spectrum of anisotropies: 5% of the total power can come from strings (see e.g. Dvorkin, Hu and Wyman, 2011). Leads to limit Gµ < / 46

23 History II String String Supergravity models of inflation typically yield cosmic strings after reheating (R. Jeannerot et al., 2003). Brane inflation models typically yield cosmic strings in the form of cosmic superstrings (Sarangi and Tye, 2002; Copeland, Myers and Polchinski, 2004). String Gas Cosmology may lead to a remnant scaling network of cosmic superstrings (R.B. and C. Vafa, 1989: A. Nayeri, R.B. and C. Vafa, 2006). renewed interest in cosmic strings as supplementary source of fluctuations. Best current limit from angular spectrum of anisotropies: 5% of the total power can come from strings (see e.g. Dvorkin, Hu and Wyman, 2011). Leads to limit Gµ < / 46

24 16 / 46 Plan 1 String String 2 String 3 String 4 5 6

25 17 / 46 Geometry of a Straight String A. Vilenkin, Phys. Rev. D 23, 852 (1981). String String Space away from the string is locally flat (cosmic string exerts no gravitational pull). Space perpendicular to a string is conical with deficit angle α = 8πGµ,

26 18 / 46 Effect N. Kaiser and A., Nature 310, 391 (1984). String Photons passing by the string undergo a relative Doppler shift δt T = 8πγ(v)vGµ, String

27 19 / 46 String String network of line discontinuities in anisotropy maps. N.B. characteristic scale: comoving Hubble radius at the time of recombination need good angular resolution to detect these edges. Need to analyze position space maps.

28 19 / 46 String String network of line discontinuities in anisotropy maps. N.B. characteristic scale: comoving Hubble radius at the time of recombination need good angular resolution to detect these edges. Need to analyze position space maps.

29 19 / 46 String String network of line discontinuities in anisotropy maps. N.B. characteristic scale: comoving Hubble radius at the time of recombination need good angular resolution to detect these edges. Need to analyze position space maps.

30 20 / 46 Signature in temperature anisotropy maps R. J. Danos and R. H. Brandenberger, arxiv: [astro-ph] x 10 0 map of the sky at 1.5 resolution String String

31 21 / 46 String String network of line discontinuities in anisotropy maps. Characteristic scale: comoving Hubble radius at the time of recombination need good angular resolution to detect these edges. Need to analyze position space maps. Edges produced by cosmic strings are masked by the background" noise.

32 22 / 46 Temperature map Gaussian + strings String String

33 String String network of line discontinuities in anisotropy maps. Characteristic scale: comoving Hubble radius at the time of recombination need good angular resolution to detect these edges. Need to analyze position space maps. Edges produced by cosmic strings are masked by the background" noise. Edge detection algorithms: a promising way to search for strings Application of Canny edge detection algorithm to simulated data (SPT/ACT specification) limit Gµ < may be achievable [S. Amsel, J. Berger and R.B. (2007), A. Stewart and R.B. (2008), R. Danos and R.B. (2008)] 23 / 46

34 String String network of line discontinuities in anisotropy maps. Characteristic scale: comoving Hubble radius at the time of recombination need good angular resolution to detect these edges. Need to analyze position space maps. Edges produced by cosmic strings are masked by the background" noise. Edge detection algorithms: a promising way to search for strings Application of Canny edge detection algorithm to simulated data (SPT/ACT specification) limit Gµ < may be achievable [S. Amsel, J. Berger and R.B. (2007), A. Stewart and R.B. (2008), R. Danos and R.B. (2008)] 23 / 46

35 24 / 46 String Wake J. Silk and A. Vilenkin, Phys. Rev. Lett. 53, 1700 (1984). Consider a cosmic string moving through the primordial gas: Wedge-shaped region of overdensity 2 builds up behind the moving string: wake. String String

36 Closer look at the wedge String Consider a string at time t i [t rec < t i < t 0 ] moving with velocity v s with typical curvature radius c 1 t i String 4!Gµtivs"s t i v s "s v c 1 t i 25 / 46

37 26 / 46 Gravitational accretion onto a wake L. Perivolaropoulos, R.B. and A., Phys. Rev. D 41, 1764 (1990). String String Initial overdensity gravitational accretion onto the wake. Accretion computed using the Zeldovich approximation. Focus on a mass shell a physical distance w(q, t) above the wake: w(q, t) = a(t) ( q ψ ), Gravitational accretion ψ grows. Turnaround: ẇ(q, t) = 0 determines q nl (t) and thus the thickness of the gravitationally bound region.

38 26 / 46 Gravitational accretion onto a wake L. Perivolaropoulos, R.B. and A., Phys. Rev. D 41, 1764 (1990). String String Initial overdensity gravitational accretion onto the wake. Accretion computed using the Zeldovich approximation. Focus on a mass shell a physical distance w(q, t) above the wake: w(q, t) = a(t) ( q ψ ), Gravitational accretion ψ grows. Turnaround: ẇ(q, t) = 0 determines q nl (t) and thus the thickness of the gravitationally bound region.

39 27 / 46 Plan 1 String String 2 String 3 String 4 5 6

40 28 / 46 Signature in R. Danos, R.B. and G. Holder, arxiv: [astro-ph.co]. String String Wake is a region of enhanced free electrons. photons emitted at the time of recombination acquire extra polarization when they pass through a wake. Statistically an equal strength of E-mode and B-mode polarization is generated. Consider photons which at time t pass through a string segment laid down at time t i < t. P Q 24π ( 3 ) 1/2σT fgµv s γ s 25 4π Ω B ρ c (t 0 )mp 1 ( ) 2 ( t 0 z(t) + 1 z(ti ) + 1 ) 1/2.

41 29 / 46 Signature in II String String Inserting numbers yields the result: P Q fgµv (z(t) + 1) 2 (z(t i ) + 1) 310 sγ s Ω 7 B Characteristic pattern in position space:

42 Is B-mode the Holy Grail of Inflation? R.B., arxiv: [astro-ph.co]. 30 / 46 String String strings produce direct B-mode polarization. gravitational waves not the only source of primordial B-mode polarization. string loop oscillations produce a scale-invariant spectrum of primordial gravitational waves with a contribution to δt /T which is comparable to that induced by scalar fluctuations (see e.g. A. Albrecht, R.B. and N. Turok, 1986). a detection of gravitational waves through B-mode polarization is more likely to be a sign of something different than inflation.

43 Is B-mode the Holy Grail of Inflation? R.B., arxiv: [astro-ph.co]. 30 / 46 String String strings produce direct B-mode polarization. gravitational waves not the only source of primordial B-mode polarization. string loop oscillations produce a scale-invariant spectrum of primordial gravitational waves with a contribution to δt /T which is comparable to that induced by scalar fluctuations (see e.g. A. Albrecht, R.B. and N. Turok, 1986). a detection of gravitational waves through B-mode polarization is more likely to be a sign of something different than inflation.

44 Is B-mode the Holy Grail of Inflation? R.B., arxiv: [astro-ph.co]. 30 / 46 String String strings produce direct B-mode polarization. gravitational waves not the only source of primordial B-mode polarization. string loop oscillations produce a scale-invariant spectrum of primordial gravitational waves with a contribution to δt /T which is comparable to that induced by scalar fluctuations (see e.g. A. Albrecht, R.B. and N. Turok, 1986). a detection of gravitational waves through B-mode polarization is more likely to be a sign of something different than inflation.

45 Is B-mode the Holy Grail of Inflation? R.B., arxiv: [astro-ph.co]. 30 / 46 String String strings produce direct B-mode polarization. gravitational waves not the only source of primordial B-mode polarization. string loop oscillations produce a scale-invariant spectrum of primordial gravitational waves with a contribution to δt /T which is comparable to that induced by scalar fluctuations (see e.g. A. Albrecht, R.B. and N. Turok, 1986). a detection of gravitational waves through B-mode polarization is more likely to be a sign of something different than inflation.

46 31 / 46 Plan 1 String String 2 String 3 String 4 5 6

47 Motivation R.B., D. Danos, O. Hernandez and G. Holder, arxiv: ; O. Hernandez, Yi Wang, R.B. and J. Fong, arxiv: / 46 String String 21 cm surveys: new window to map the high redshift universe, in particular the dark ages". strings produce nonlinear structures at high redshifts. These nonlinear structures will leave imprints in 21 cm maps. (Khatri & Wandelt, arxiv: , A. Berndsen, L. Pogosian & M. Wyman, arxiv: ) 21 cm surveys provide 3-d maps potentially more data than the. 21 cm surveys is a promising window to search for cosmic strings.

48 Motivation R.B., D. Danos, O. Hernandez and G. Holder, arxiv: ; O. Hernandez, Yi Wang, R.B. and J. Fong, arxiv: / 46 String String 21 cm surveys: new window to map the high redshift universe, in particular the dark ages". strings produce nonlinear structures at high redshifts. These nonlinear structures will leave imprints in 21 cm maps. (Khatri & Wandelt, arxiv: , A. Berndsen, L. Pogosian & M. Wyman, arxiv: ) 21 cm surveys provide 3-d maps potentially more data than the. 21 cm surveys is a promising window to search for cosmic strings.

49 Motivation R.B., D. Danos, O. Hernandez and G. Holder, arxiv: ; O. Hernandez, Yi Wang, R.B. and J. Fong, arxiv: / 46 String String 21 cm surveys: new window to map the high redshift universe, in particular the dark ages". strings produce nonlinear structures at high redshifts. These nonlinear structures will leave imprints in 21 cm maps. (Khatri & Wandelt, arxiv: , A. Berndsen, L. Pogosian & M. Wyman, arxiv: ) 21 cm surveys provide 3-d maps potentially more data than the. 21 cm surveys is a promising window to search for cosmic strings.

50 Motivation R.B., D. Danos, O. Hernandez and G. Holder, arxiv: ; O. Hernandez, Yi Wang, R.B. and J. Fong, arxiv: / 46 String String 21 cm surveys: new window to map the high redshift universe, in particular the dark ages". strings produce nonlinear structures at high redshifts. These nonlinear structures will leave imprints in 21 cm maps. (Khatri & Wandelt, arxiv: , A. Berndsen, L. Pogosian & M. Wyman, arxiv: ) 21 cm surveys provide 3-d maps potentially more data than the. 21 cm surveys is a promising window to search for cosmic strings.

51 33 / 46 The Effect String String 10 3 > z > 10: baryonic matter dominated by neutral H. Neutral H has hydrogen hyperfine absorption/emission line. String wake is a gas cloud with special geometry which emits/absorbs 21cm radiation. Whether signal is emission/absorption depends on the temperature of the gas cloud.

52 33 / 46 The Effect String String 10 3 > z > 10: baryonic matter dominated by neutral H. Neutral H has hydrogen hyperfine absorption/emission line. String wake is a gas cloud with special geometry which emits/absorbs 21cm radiation. Whether signal is emission/absorption depends on the temperature of the gas cloud.

53 33 / 46 The Effect String String 10 3 > z > 10: baryonic matter dominated by neutral H. Neutral H has hydrogen hyperfine absorption/emission line. String wake is a gas cloud with special geometry which emits/absorbs 21cm radiation. Whether signal is emission/absorption depends on the temperature of the gas cloud.

54 33 / 46 The Effect String String 10 3 > z > 10: baryonic matter dominated by neutral H. Neutral H has hydrogen hyperfine absorption/emission line. String wake is a gas cloud with special geometry which emits/absorbs 21cm radiation. Whether signal is emission/absorption depends on the temperature of the gas cloud.

55 34 / 46 t String String!v!v

56 35 / 46 Key general formulas String String Brightness temperature: Spin temperature: T b (ν) = T S ( 1 e τ ν ) + Tγ (ν)e τν, T S = 1 + x c 1 + x c T γ /T K T γ. T K : gas temperature in the wake, x c collision coefficient Relative brightness temperature: δt b (ν) = T b(ν) T γ (ν) 1 + z

57 36 / 46 String String Optical depth: τ ν = 3c2 A 10 ( ν )N HI 4ν 2 k B T S 4 φ(ν), N HI column number density of hydrogen atoms. Frequency dispersion Line profile: δν ν = 2sin(θ) tan θ Hw c, φ(ν) = 1 δν for ν ɛ [ν 10 δν 2, ν 10 + δν 2 ],

58 Application to String String String Wake temperature T K : T K [20 K](Gµ) 2 6 (v sγ s ) 2 z i + 1 z + 1, determined by considering thermalization at the shock which occurs after turnaround when w = 1/2w max (see Eulerian hydro simulations by A. Sornborger et al, 1997). Thickness in redshift space: δν ν = 24π 15 Gµv sγ s ( zi + 1 ) 1/2( z(t) + 1 ) 1/ (Gµ) 6 (v s γ s ), using z i + 1 = 10 3 and z + 1 = 30 in the second line. 37 / 46

59 Application to String String String Wake temperature T K : T K [20 K](Gµ) 2 6 (v sγ s ) 2 z i + 1 z + 1, determined by considering thermalization at the shock which occurs after turnaround when w = 1/2w max (see Eulerian hydro simulations by A. Sornborger et al, 1997). Thickness in redshift space: δν ν = 24π 15 Gµv sγ s ( zi + 1 ) 1/2( z(t) + 1 ) 1/ (Gµ) 6 (v s γ s ), using z i + 1 = 10 3 and z + 1 = 30 in the second line. 37 / 46

60 38 / 46 Relative brightness temperature: String String x c ( T γ ) δt b (ν) = [0.07 K] 1 (1 + z) 1/2 1 + x c T K 200mK for z + 1 = 30. Signal is emission if T K > T γ and absorption otherwise. Critical curve (transition from emission to absorption): (Gµ) (v 2 (z + 1)2 sγ s ) z i + 1

61 38 / 46 Relative brightness temperature: String String x c ( T γ ) δt b (ν) = [0.07 K] 1 (1 + z) 1/2 1 + x c T K 200mK for z + 1 = 30. Signal is emission if T K > T γ and absorption otherwise. Critical curve (transition from emission to absorption): (Gµ) (v 2 (z + 1)2 sγ s ) z i + 1

62 Scalings of various temperatures 500 String String T K z Top curve: (Gµ) 6 = 1, bottom curve: (Gµ) 6 = / 46

63 40 / 46 Geometry of the signal String String x c x 2 x 1 # t t 0 s 1 s 2 2t i t i!! 2 1! x x 2 1 "! x c

64 41 / 46 Extension 1: Diffuse" String O. Hernandez and R.B., arxiv: String String also form for T K < T g, but no shock heating The wakes are more dilute thicker but less dense. h w (t) TK <T g T g = h w (t) Tg=0 T K This allows the exploration of smaller values of Gµ.

65 41 / 46 Extension 1: Diffuse" String O. Hernandez and R.B., arxiv: String String also form for T K < T g, but no shock heating The wakes are more dilute thicker but less dense. h w (t) TK <T g T g = h w (t) Tg=0 T K This allows the exploration of smaller values of Gµ.

66 41 / 46 Extension 1: Diffuse" String O. Hernandez and R.B., arxiv: String String also form for T K < T g, but no shock heating The wakes are more dilute thicker but less dense. h w (t) TK <T g T g = h w (t) Tg=0 T K This allows the exploration of smaller values of Gµ.

67 41 / 46 Extension 1: Diffuse" String O. Hernandez and R.B., arxiv: String String also form for T K < T g, but no shock heating The wakes are more dilute thicker but less dense. h w (t) TK <T g T g = h w (t) Tg=0 T K This allows the exploration of smaller values of Gµ.

68 42 / 46 String String T b ze20 K z i 3000 Red to 1000 Blue GΜ 6

69 43 / 46 Extension 2: String Loops M. Pagano and R.B., arxiv: (2012). String String string loops sees nonlinear objects at high redshift. Spherical accretion Average overdensity 64 (compared to 4 for a wake) higher brightness temperature! But: no string-specific geometrical signal harder to identify loop signals compared to wake signals.

70 43 / 46 Extension 2: String Loops M. Pagano and R.B., arxiv: (2012). String String string loops sees nonlinear objects at high redshift. Spherical accretion Average overdensity 64 (compared to 4 for a wake) higher brightness temperature! But: no string-specific geometrical signal harder to identify loop signals compared to wake signals.

71 43 / 46 Extension 2: String Loops M. Pagano and R.B., arxiv: (2012). String String string loops sees nonlinear objects at high redshift. Spherical accretion Average overdensity 64 (compared to 4 for a wake) higher brightness temperature! But: no string-specific geometrical signal harder to identify loop signals compared to wake signals.

72 43 / 46 Extension 2: String Loops M. Pagano and R.B., arxiv: (2012). String String string loops sees nonlinear objects at high redshift. Spherical accretion Average overdensity 64 (compared to 4 for a wake) higher brightness temperature! But: no string-specific geometrical signal harder to identify loop signals compared to wake signals.

73 44 / 46 Plan 1 String String 2 String 3 String 4 5 6

74 45 / 46 String String strings nonlinearities already at high redshifts. cosmic strings more pronounced at high redshifts. strings lead to perturbations which are non-gaussian. strings predict specific geometrical patterns in position space. 21 cm surveys provide an ideal arena to look for cosmic strings. string wakes produce distinct wedges in redshift space with enhanced 21cm absorption or emission.

75 45 / 46 String String strings nonlinearities already at high redshifts. cosmic strings more pronounced at high redshifts. strings lead to perturbations which are non-gaussian. strings predict specific geometrical patterns in position space. 21 cm surveys provide an ideal arena to look for cosmic strings. string wakes produce distinct wedges in redshift space with enhanced 21cm absorption or emission.