Weak lensing
Definition: Small coherent distortions of background images produced by foreground gravitational potentials.
Why it matters here: It is required to answer How can tiny image distortions reveal matter? and to distinguish direct observation from cosmological inference.
Relationships: Read it with Cosmic shear, the model \(gamma_t(R) approximately [barSigma(<R)-Sigma(R)]/Sigma_crit\), and the evidence statement The DES Y3 paper is the cited source; the package uses only its published parameter summaries and a clearly synthetic geometry illustration, not shear catalogs or correlation-function vectors.
Boundary or common confusion: S8= sigma8 sqrt(Omega_m/0.3) compresses a degeneracy direction; it is not a direct measurement of sigma8 alone.
Cosmic shear
Definition: The two-point statistical pattern of weak-lensing distortions across source galaxies.
Why it matters here: It is required to answer How can tiny image distortions reveal matter? and to distinguish direct observation from cosmological inference.
Relationships: Read it with Tangential shear, the model \(gamma_t(R) approximately [barSigma(<R)-Sigma(R)]/Sigma_crit\), and the evidence statement The DES Y3 paper is the cited source; the package uses only its published parameter summaries and a clearly synthetic geometry illustration, not shear catalogs or correlation-function vectors.
Boundary or common confusion: S8= sigma8 sqrt(Omega_m/0.3) compresses a degeneracy direction; it is not a direct measurement of sigma8 alone.
Tangential shear
Definition: The component of image distortion aligned tangentially around a foreground lens.
Why it matters here: It is required to answer How can tiny image distortions reveal matter? and to distinguish direct observation from cosmological inference.
Relationships: Read it with Critical surface density, the model \(gamma_t(R) approximately [barSigma(<R)-Sigma(R)]/Sigma_crit\), and the evidence statement The DES Y3 paper is the cited source; the package uses only its published parameter summaries and a clearly synthetic geometry illustration, not shear catalogs or correlation-function vectors.
Boundary or common confusion: S8= sigma8 sqrt(Omega_m/0.3) compresses a degeneracy direction; it is not a direct measurement of sigma8 alone.
Critical surface density
Definition: The lens-source geometry factor converting projected mass contrast into shear.
Why it matters here: It is required to answer How can tiny image distortions reveal matter? and to distinguish direct observation from cosmological inference.
Relationships: Read it with S8, the model \(gamma_t(R) approximately [barSigma(<R)-Sigma(R)]/Sigma_crit\), and the evidence statement The DES Y3 paper is the cited source; the package uses only its published parameter summaries and a clearly synthetic geometry illustration, not shear catalogs or correlation-function vectors.
Boundary or common confusion: S8= sigma8 sqrt(Omega_m/0.3) compresses a degeneracy direction; it is not a direct measurement of sigma8 alone.
S8
Definition: The compressed amplitude combination sigma8 sqrt(Omega_m/0.3) aligned with a common lensing degeneracy.
Why it matters here: It is required to answer How can tiny image distortions reveal matter? and to distinguish direct observation from cosmological inference.
Relationships: Read it with Weak lensing, the model \(gamma_t(R) approximately [barSigma(<R)-Sigma(R)]/Sigma_crit\), and the evidence statement The DES Y3 paper is the cited source; the package uses only its published parameter summaries and a clearly synthetic geometry illustration, not shear catalogs or correlation-function vectors.
Boundary or common confusion: S8= sigma8 sqrt(Omega_m/0.3) compresses a degeneracy direction; it is not a direct measurement of sigma8 alone.