Past exam of the mathematics course of the University of Cambridge 2014 iii Paper 43 3 a Solution Created 2026-10-03 Updated 2026-10-06
In the Polonyi model, the Kähler metric is . The relevant Kähler covariant derivative of a superpotential isThe supergravity auxiliary field is , up to an irrelevant common phase convention. Thus a constant vacuum preserves supersymmetry exactly when this auxiliary field vanishes. For , the superpotential and scalar potential vanish identically, and every constant scalar value is a supersymmetric vacuum.
For , put . Its supersymmetry condition becomesSince , it requires and . Hence the Polonyi supersymmetry branches areAt these points , so the supergravity F-term potential is negative, : these are supersymmetric Anti-de Sitter spacetime vacua, not zero-energy ones. The condition also makes them stationary, as follows by differentiating the supergravity F-term potential.
For and , the auxiliary field cannot vanish anywhere, so any vacuum has supersymmetry breaking. For , a stationary vacuum at any other scalar value still breaks supersymmetry; the parameter condition alone does not determine which vacuum is selected. In particular, a nontrivial zero-energy vacuum cannot preserve supersymmetry: and would also imply , whereas gives and .
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 309 3 Solution Created 2026-10-03 Updated 2026-10-14
The rotational Killing vector fields of the spherical symmetry conserve the angular-momentum vector. Its direction is fixed, so every nonradial orbit lies in the plane through the symmetry centre orthogonal to that vector. A spatial rotation can make this the equatorial plane. Equivalently, the initial conditions and solve the equation uniquely. This is the planarity of geodesics in spherical symmetry; a radial geodesic has zero angular momentum and may be assigned any plane.
On , the cyclic coordinates and produce geodesic conserved quantities from Killing vectors,For a timelike geodesic parametrized by proper time, the proper-time normalization is . Substitution of and gives the first-order radial equationThis is the timelike geodesic effective potential for static Anti-de Sitter spacetime with curvature radius one.
A geodesic passing through must have . If it moves away from the origin, , andTaking proper time at departure givesIt turns around at and first returns to the origin atThis energy-independent refocusing is the characteristic radial timelike geodesic in anti-de Sitter spacetime result; for curvature radius , the answer is .
Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 354 1 c Solution Created 2026-09-24 Updated 2026-09-25
The state–operator correspondence maps to the lowest one-particle state on . On a sphere of radius , cylinder energy equals scaling dimension divided by . The primary has .
A translation generator raises the dimension by one and transforms as a vector of . States with no angular momentum arise from scalar descendant pairs , so the allowed descendants areTheir dimensions are , and hence the one-quantum, zero-angular-momentum energies areThese are the normal-mode energies of a massless scalar in global Anti-de Sitter spacetime.
Curvature contractions. Use the index contraction stipulated in the question. In three dimensions,The same contraction in four dimensions givesThen the Ricci scalar is and the Einstein tensor is . Thus is precisely the vacuum Einstein field equations .
The static solution. For , and . The given Ricci tensor components becomeEach equals times the corresponding metric tensor component. ThereforeThis is Anti-de Sitter spacetime in static coordinates on anti-de Sitter spacetime, with curvature radius . The overall metric signature is opposite to the convention used in some descriptions of those coordinates; the geodesic constants below use the question's convention.
Conserved quantities and radial motion. In the equatorial plane, the geodesic Lagrangian is . Its cyclic coordinates giveFor rest mass , is the conserved Killing energy and is the axial angular momentum. Timelike normalization givesFor purely radial motion , differentiating away from a turning point gives , and continuity extends that equation through the turning point. An outward launch from the origin at hasThis is the radial timelike geodesic in anti-de Sitter spacetime. Its first return to the origin isindependent of the outward launch speed for every nontrivial launch . The coordinate is nonnegative, so this sine expression describes the excursion up to that return; subsequent passage through the origin requires changing the radial direction or using a signed diameter coordinate. The speed changes the amplitude, not the harmonic frequency.
Circular periods. The effective radial potential is . For a circle at , gives , and normalization gives . Thus and . A stable circular timelike geodesic in anti-de Sitter spacetime therefore hasindependently of radius. This is the same isochronous behavior as the central harmonic radial equation. A static clock placed at the orbit's radius instead measures , which does depend on radius; it is a different clock from the orbiting particle's proper time.
For Lorentzian boundary metric and , this Anti-de Sitter spacetime patch has unit curvature radius. Its orthonormal coframe has connection and curvature , giving sectional curvature . The full local isometry algebra is in spacetime dimension . A patch need not support every local Killing flow for all parameter values.
