Cosmic strings and the gravitational-wave background
A cosmic string is a thin line of trapped energy left by the early universe. Start with one loop, see how it radiates and shrinks, add up every generation of loops into a background, then check a published number yourself and read what pulsar timing has found.
L1 · Concept
Why could a thin cosmic string shape a whole gravitational-wave spectrum?
A string network keeps cutting off loops. Each loop rings at a pitch set by its size, so loops from every era spread one signal over many decades of frequency.
L1 · Chapter
What the tension of a cosmic string measures
Work out how heavy a cosmic string is per metre, why one dimensionless number sets its gravity, and how a scaling network keeps producing loops.
L2 · Chapter
How a cosmic-string loop radiates and shrinks
Follow one Nambu–Goto loop: its period, the cusps that beam bursts, the harmonics it emits and the steady shrinking that ends its life.
L3 · Chapter
From a loop population to the background spectrum
Build the loop number density, integrate its emission over redshift and derive why the radiation-era plateau grows as the square root of tension.
L3 · Method
Recompute the radiation-era plateau of a cosmic-string background
Rerun a fixed Nambu–Goto loop model, compare it with the published plateau formula and see which checks fail when one step is wrong.
L4 · Paper guide
Reading pulsar-timing and LISA results on cosmic strings
Which NANOGrav 15-year figures constrain string tension, why a good spectral fit is not a detection, and what LISA forecasts can and cannot separate.