The axion is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a certain range, they are of interest as a possible component of cold dark matter.
As shown by Gerardus 't Hooft, strong interactions of the standard model, QCD, possess a non-trivial vacuum structure that in principle permits the violation of the combined symmetries of charge conjugation and parity, collectively known as CP. Together with effects generated by the weak interactions, the effective strong CP violating term, Θ, appears as a Standard Model input parameter—it is not predicted by the theory, but must be measured. However, large CP violating interactions originating from QCD would induce a large electric dipole moment for the neutron. (While the neutron is an electrically neutral particle, nothing prevents charge separation within the neutron itself.) Experimental constraints on the currently unobserved neutron's electric dipole moment imply that CP violation arising from QCD must be extremely tiny and thus Θ must itself be extremely small or absent. Since a priori Θ could have any value between 0 and 2π (the parameter is periodic), this presents a naturalness problem for the standard model. Why should this parameter find itself so close to 0? (Or, why should QCD find itself CP-preserving?) This question constitutes what is known as the strong CP problem.
You may know me too well
From spending last night in that puddle
Kickin' my heart off in the trow
You tore a pity hole in your sock
You said "I will not join in your game"
Burnin' down whole houses of ice cream vendors
So please let them do whatever they may
For they have had every right
To make their living
To make their living
To make their living
To make their living
To make their living
You may know me too well
You may know me too well
You may know me too well
I hear you've got a child somewhere
A castaway; a little ape
A drift on the waves
And if I was a servant girl
Would you treat me the same?
Blow the dust from my grave?
Keep the IV in me?
Chase the critters away?
You mother was of a crippled heart
Lost her crutch in the dark
Crawled a mile too far
Washed up by the beach
Now she tends to the sea
Starfish, anemone
Other misplaced things (Repeat)
She bends by degrees so gracefully
Picking up twigs, wild seeds
They took us by the edge of the desert
And they laid them down in the sand
Carrie picked at her nails in the sunshine
Solid just stayed in the van
On the old high orchard she had asked him
To promise her that he'd never leave
He would've died at the outskirts of towers
The night he started having the dreams
She chased him all the way to the border
But he was only picking up speed
He doubled back and finally lost her
By rolling into a ravine
But he could still hear her crying behind him
From the rocky bank where he hid
He doubled his shoulders right up to his chin and stared up at the firmament
They found him with his eyes wide open
At a place called the joshua tree
"I'll never go away for good," he said
He promised her that he'd never leave
I feel a sickness coming on
It'll scare my bones and cross the law
And I've been poisoned by a song
It's hard to tell where I fell, what went wrong
You reach a point where you can let
Your mind run free in wonder
And you will dig in with the spurs
And lead the beast to water
I know you'll miss the open plains
Where the sky rolls off to nothing
You will gather up the reigns
And leave it all behind you
It's all over Idaho
We're kickin' up your dust and burnin' up your gasoline
And every one of us has bugs crawlin' through our veins
We can't pretend to be pure and free
So who will be the next to run?
One guy walked off to die and left us with nothin' to swallow but the stars
I see him everywhere and each unshaven refugee
Nursing last night's fire
Who will be the next to run?
Who will be the next to bail on out of this ride
And leave us dry?
Who will be the next to run?
Who will be the next to bail on out of this ride
Bail on out of this ride
Bail on out of this ride
Bail on out of this ride
Starshot, halo-bound
So laying me out
You got flaxen wings of hayseed
And something under your arm
And may I please touch
Your fancy tattered cloak
Were its holes divinely fabricated
Or were they eaten out by a moth?
...Eaten out by a moth? (Repeat)
What's that beautiful instrument that you bear?
You did not design that by chance
You were touching a dulcimer's fancy