Probing the scale of grand unification
with gravitational waves
Valerie Domcke
CERN/EPFL

gravitationalwaves@ Lomonosov conference
23.08.2021
based on1912.03695, 2009.10649, 2107.04578
w. W. Buchmüller, H. Murayama
and K. Schmitz

Valerie Domcke - CERN/EPFL

cosmic strings in a nutshell● one-dimensional topological defects formed in an early Universe phase transition● symmetry breaking pattern●produces cosmic strings iff

form cosmic string network, evolves through•string (self-)intersection & loop formation•emission of particles and gravitational waves
Allen & Shellard `90

Probing the GUT scale with GWs

2 / 14

Valerie Domcke - CERN/EPFLmetastable cosmic strings
Vilenkin `82; Leblond, Shlaer, Siemens `09;
Monin, Voloshin `08/09; Dror et al `19

considercosmic strings
no cosmic strings

Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFLmetastable cosmic strings
Vilenkin `82; Leblond, Shlaer, Siemens `09;
Monin, Voloshin `08/09; Dror et al `19

considercosmic strings
no cosmic strings

resolution: no topologically stable cosmic strings
generates monopoles

generates cosmic strings,

Probing the GUT scale with GWs

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metastablestring &monopole
network

Valerie Domcke - CERN/EPFLmetastable cosmic strings
Vilenkin `82; Leblond, Shlaer, Siemens `09;
Monin, Voloshin `08/09; Dror et al `19

considercosmic strings
no cosmic strings

resolution: no topologically stable cosmic strings
generates monopoles
cosmic inflation

dilutes monopoles
generates cosmic strings,

metastablestring &monopole
network

decay via Schwinger production of monopoles

Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

gravitational wave signal - SGWB
see eg. Auclair, Blanco-Pillado, Figuera et al `19

gravitational wave emission from integration over loop distribution function:
GW power spectrum of a single loop
# of loops emitting GWs
observed at frequency f today# of loops with length

at time twith
cosmological history

Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

gravitational wave signal - SGWB
see eg. Auclair, Blanco-Pillado, Figuera et al `19

gravitational wave emission from integration over loop distribution function:
GW power spectrum of a single loop
# of loops emitting GWs
observed at frequency f today# of loops with length

at time twithcosmological history

finte CS life timenumber density
for stable strings

decay due to monopole
production and GW
emission

Buchmüller, VD, Schmitz `21

Blanco-Pillado, Olum, Shlaer ‘14

Probing the GUT scale with GWs

loop production onlyin scaling regime

4 / 14

Valerie Domcke - CERN/EPFL

gravitational wave spectrum
stable cosmic strings(highly constrained by PTA)metastable cosmic strings
discovery space for LISA, LIGO & beyond

PTALISA

LIGO

h2Ωgw

10-8

10-10
ET

10-12
κ=8Gμ = 10-7
10-8
10-9
10-10
10-11

κ=7loops

10-14 -10
10

10-8

10-6

10-4

f [Hz]
withProbing the GUT scale with GWs

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1100
Buchmüller, VD, Schmitz `21

can be tested with GWs!
Valerie Domcke - CERN/EPFL

NANOGrav: A first glimpse of the SGWB?
Pulsar timing array NANOGrav, Sept 2020:“Our analysis finds strong evidence of astochastic process, modeled as a power-law,with common amplitude and spectral slope
across pulsars.“„However, we find no statistically significant
evidence that this process has quadrupolar
spatial correlations, which we would consider
necessary to claim a GWB detection
consistent with General Relativity.“NANOGrav collaboration `20

Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

Parkes Pulsar timing array
PPTA `21, 2107.12112

no significant detection ofquandropolar spatial correlation

amplitude and spectral tilt
compatitive with NANOGrav

Maybe. Stay tuned for more data!
Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

cosmic strings at PTAs ?
10-7

PTA bound (2015)9.2
κ = 8.3h2 Ωgw (3 nHz)

10-8

8.2

10-9
10-10
10-11
10-12

8.1

NANOGrav
PPTA

Gμ = 10-7
10-8
10-9
10-10
10-11

0.0

loops

0.5

1.0

1.5

2.0nt (3 nHz)
Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

Prospects for GW searches

PTA hint will be probed with interferometers
Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFLparameter space of metastable strings
Buchmüller, VD, Schmitz `12
Buchmüller, VD, Murayama, Schmitz `20

metastable GUT- scale strings are testable
Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

Conclusions & Outlook● Metastable cosmic strings are a fairly generic byproduct of GUTs

with large stochastic GW signals possible at PTAs, LIGO or LISA
testable with upcoming GW detectors● Excess noise observed in NANOGrav and PPTA data may be thefirst glimpse at a SGWB- amplitude & tilt compatible with metastable cosmic strings- also compatible with super-massive BH mergers- no detection of quadrupolar signature (yet). More careful
scrutiny of data & data analysis needed

Probing the GUT scale with GWs

11 / 14

Valerie Domcke - CERN/EPFL

Conclusions & Outlook● Metastable cosmic strings are a fairly generic byproduct of GUTs

with large stochastic GW signals possible at PTAs, LIGO or LISA
testable with upcoming GW detectors● Excess noise observed in NANOGrav and PPTA data may be thefirst glimpse at a SGWB
- amplitude & tilt compatible with metastable cosmic strings- also compatible with super-massive BH mergers- no detection of quadrupolar signature (yet). More careful
scrutiny of data & data analysis needed

Questions ?
Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

backup slides

Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

GWs from segments
PTA

LISA

LIGO

h2Ωgw

10-8

10-10
Gμ = 10-7
10-9
10-11

10-12

loops
segments from loops
all contributions,10-14 -101010-8

κ=810-6

segments from strings

10-4

0.01

1100

f [Hz]
Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL

Prospects

Probing the GUT scale with GWs

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Valerie Domcke - CERN/EPFL