Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/pulsar/ppta/uploads/GWW3/XSiemens_GWW2009.pdf Дата изменения: Tue Sep 14 05:26:58 2010 Дата индексирования: Tue Sep 14 23:32:21 2010 Кодировка: Поисковые слова: gravitational radiation

Gravitational waves from cosmological sources in the pulsar timing band
Xavier Siemens Collaborators: Jolien Creighton, Larry Price


Summary

· Possible cosmological sources:


Inflation Cosmic strings Phase transitions





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Gravitational waves from cosmic strings
Linear high density objects that move relativistically Known for 30 years (Kibble 1976), may form in the early universe in phase transitions. These strings are classical solutions of field theory They are characterized by an energy scale given by the temperature of the universe when they form:

U (1) - 1
Gµ =
Picture of a Hubble volume containing strings (yellow) and closed loops (red)



mp

2

µ

2

(Allen & Shellard)

Very generic! In string theory inspired models, they called cosmic superstrings. Also in SUSY GUTs.


Cosmic strings & superstrings
Scaling solution: Energy density of string network is a small fixed fraction of radiation or matter densities; statistical quantities scale with cosmic time. Scaling possible because strings reconnect, and form loops which radiate gravitationally, shrink and eventually disappear Size at which loops are formed understood. Two proposals: (1) horizon scale, (2) size given by smoothing scale of wiggles on still not size given by gravitational the strings


Cosmic strings & superstrings
Cosmic superstrings don't always reconnect--they reconnect with probability p. Effect is to increase the time it takes the network to reach equilibrium and to increase the amount of string at equilibrium

10

-3

p1

Sarangi, Tye, Polchinksi, Jones, Jackson, Copeland, Myers, Burgess, Dvali, Vilenkin

Also more than one kind of string, and bound states. Complicated dynamics and phenomenology that have started to be explored:
Firouzjahi, Brandenberger, Karouby, Khosravi, Sakellariadou, Davis, Nelson, Rajamanoharan, Wyman, Leblond, Shlaer Binetruy, Bohe, Hertog, Bevis, Copeland, Martin, Niz, Pourtsidou, Saffin, Rivers, Steer


The gravitational signal produced by a cusp
· Cusps are regions of string that
instantaneously acquire huge Lorentz boosts linearized Einstein Eqs.

· Metric perturbation is computed using · Waveform is generic: All cusps are the same
[Berezinsky, Hnatyk, and Vilenkin, 00; Damour and Vilenkin, 00, 01, 05]
cusp observation direction

h(f ) = Af

-4/3

(fh - f )(f - fl )

· High frequency cutoff fh depends on cusp direction · Low frequency cutoff fl is cosmological, in practice
depends on instrument Cusps are pointy, gravitational wave has very high frequency content


Stochastic background of a cosmic string network
· For large (horizon-sized) loops vary reconnection probability and
timing Pulsar

BBN
LIGO Initial

If loops are large : Pulsar timing (2006 PPTA limit, Jenet et. al) rules out everything detectable by Initial LIGO

Burst LIGO Initial

GUT scale

LIGO Initial

XS, V. Mandic, J. Creighton, Phys. Rev. Lett. 98 (2007) 111101

Gµ =

mp

2


Recent LIGO results for the stochastic background
[B. Abbott et al., Nature 460, 990-994 (2009)]

(f 100Hz) < 7 в 10

-6

· For loop sizes given by gravitational smoothing of wiggles:
10 10 10 10 10 10 10
0

p = 10-3

-2

-4

-6

-8

S4 S5 Pulsar BBN CMB Planck LIGO Burst

loop size

-10

-12

10

-9

10

-8

Gµ

10

-7

10

-6


Gravitational waves from other cosmological processes
10
8

GW frequency today for early universe processes

Experiment
10
6

GUT

10

4

10

2

LIGO/Virgo/GEO/ET BBO/Decigo LISA PTA QCD
-2

10
f [Hz]

0

10

-2

10

-4

10

-6

Electroweak

10

-8

10

-10

10

10

0

10

2

10

4

10 10 Energy [GeV]

6

8

10

10

10

12

10

14

Theory

10

16

9


Gravitational waves from other early universe processes: Preheating
· The early universe underwent a period of exponential expansion which made it flat, homogenous, and isotropic · Inflation is usually modeled using a scalar field subject to a potential V ().



called the inflaton which is

V ()
Inflation

Reheating Field rolls around minimum of potential


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Gravitational waves from preheating
· This process can lead to gravitational wave production. There is a particularly violent era in reheating (right at the start), called pre-heating where the inflaton induces parametric resonances in another field it is coupled to: exponentially excites certain modes. · Most familiar example of parametric resonance is a child on a swing

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Other examples: EW Phase transition in simple extension of SM
· Phase transitions: Bubble collisions and turbulent plasmas · EW phase transition in simple extension of SM

Ashoorioon & Kostandin (2009)

· We're scoping out QCD phase transition with Chiara Caprini and Ruth Durrer
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