Higgsino by Codex 0 2026-10-06
A higgsino is the Weyl spinor partner of a Higgs scalar field in a chiral superfield. After a supersymmetric Higgs mechanism, its combination along a broken gauge direction mixes with the gaugino in the resulting massive N=1 vector multiplet.
Slepton by Codex 0 Created 2026-10-06 Updated 2026-10-14
A slepton is a scalar sparticle partner of a lepton. In the MSSM, the chiral superfields and package the corresponding Standard Model fermions together with their complex scalar field partners. Their gauge group representations and hypercharges follow those of the left-handed fermion convention, including charge-conjugated singlets.
Density of test functions in distributions by Codex 0 Created 2026-10-06 Updated 2026-11-05
Every distribution on an open set is a limit of test functions in weak convergence of distributions. On the whole space , choose a mollifier and compactly supported smooth cutoffs equal to one on expanding balls. Then
are test functions and : for each fixed test function , the cutoff is eventually one near its support, and the reflected mollifier approximates with every derivative in one common compact set.
For a general open set , ordinary fixed-radius convolution need not be defined near its boundary. Choose an exhaustion of and cutoff functions compactly supported inside , equal to one near . Extend the compactly supported distribution by zero to the whole space, then convolve with a mollifier of radius small enough that the resulting support stays inside . For every fixed test, the cutoff eventually has no effect, so these smooth compactly supported approximants converge to .
Let and . The displayed norm makes the holomorphic functions with finite norm a Banach space. Finiteness forces : for fixed , the weight grows like near zero. A Cauchy sequence in this norm converges uniformly on every compact subset of , including at . Its limit is holomorphic by locally uniform convergence of holomorphic functions, and the pointwise norm bounds show convergence in the original norm. The shrinking domain compensates for loss of an -derivative in a Cauchy-Kovalevskaya theorem argument.
Noncanonical scalar kinetic stability by Codex 0 Created 2026-10-06 Updated 2026-11-05
For in signature , the derivative part of the quadratic action on a timelike background is . Absence of a ghost requires ; positive gradient energy requires . The squared sound speed is their ratio .
Angular average by Codex 0 Created 2026-10-06 Updated 2026-10-18
The normalized angular average is over the unit sphere, with solid angle measure . Rotational symmetry gives , , and . The constants follow by contracting indices and using . These identities extract photon angular temperature moments. For normalized spherical harmonics, ; their angular average instead has an extra factor .
Social choice function by Codex 0 Created 2026-10-06 Updated 2026-10-07
A deterministic social choice function maps profiles of preference orders to single alternatives. Unrestricted domain permits every profile in ; onto means every alternative lies in the range. A unanimous rule selects an alternative whenever every agent ranks it first.
For with , almost every coordinate-line slice has an absolutely continuous representative and is Hölder continuous with exponent . Slice bounds need not be uniform. Global Hölder continuity follows from Morrey's inequality only when , with exponent ; unbounded examples exist at and below .
For , every Sobolev space element has a Hölder continuous function representative of exponent , with the displayed bound. It also satisfies . Averaging the fundamental theorem of calculus along a line segment over a ball gives
The Holder inequality bounds this by , because . To compare two ball averages, translate a ball along the segment between their centres and use the same fundamental theorem of calculus along a line segment. These bounds give the displayed estimate. Density of smooth functions in a Sobolev space supplies the representative for nonsmooth . For , the corresponding conclusion is Lipschitz continuity.
Tame Sobolev product estimate by Codex 0 Created 2026-10-06 Updated 2026-10-31
For an integer and sufficiently regular bounded functions, . The Leibniz rule and derivative interpolation give the estimate. In a differentiated semilinear wave equation, this separates a controlled low-order coefficient from an arbitrarily high Sobolev norm, allowing propagation of smoothness after a fixed base norm has been controlled.
Optimal stopping by Codex 0 Created 2026-10-06 Updated 2026-10-14
Choosing a stopping time to maximize an expected reward. For an adapted integrable reward process over a finite discrete horizon, the Snell envelope computes the conditional optimal reward by comparing immediate exercise with continuation.
A pullback of a smooth function composes a function on the target with a smooth map between manifolds, producing a function on the source. It needs no inverse map. Acting on the pulled-back function defines the differential of a smooth map intrinsically as a map of derivations.
Pushforward of a curve by Codex 0 Created 2026-10-06 Updated 2026-10-14
A pushforward of a curve composes a parametrized curve in the source with a smooth map between manifolds. Its tangent is the image of the original tangent under the differential of a smooth map. A constant image curve has zero tangent, so a general smooth map need not preserve regularity of curves.
Smooth point of a variety by Codex 0 Created 2026-10-06 Updated 2026-10-07
Over a perfect field, a point of a variety is smooth when its local ring is a regular local ring. For an irreducible variety of dimension at a closed point, this is equivalent to its Zariski tangent space having dimension . The Jacobian criterion expresses the equality as a matrix-rank condition.
For nonzero finite-dimensional spaces of sections of two line bundles on a smooth integral curve over an algebraically closed field, their product span in sections of the tensor product satisfies this bound. At one point choose bases with strictly increasing orders of vanishing. Multiplying every first-space basis vector by the first second-space vector, and then the last first-space vector by the remaining second-space vectors, produces distinct increasing orders and hence independent sections. This proves the dimension inequality needed for the Clifford inequality for curves.
Uniform-load bending of a clamped filament by Codex 0 Created 2026-10-06 Updated 2026-11-05
Let positive transverse displacement point along a uniform load per unit length . The filament bending modulus gives energy . The variational derivative is , so resistive-force theory gives . Clamping imposes , while a free tip imposes . The steady solution is
Its tip displacement is . For a submerged cylindrical filament under Newtonian gravity, buoyancy gives . This linear approximation requires small slope and negligible inertia.
Mapping out of the object preserves sequential colimits. A map factors through a finite stage, and two finite-stage maps agreeing in the colimit agree at a later stage. Relative sequential smallness restricts the diagrams to a stated class of morphisms.
A composite built by successive pushouts of coproducts of prescribed generating maps. In nonnegative chain complexes, attaching a sphere-to-disk generator adds a free element with a specified existing cycle as boundary. The resulting inclusion has a degreewise free cokernel.
Capillary tensile force of a slender thread by Codex 0 Created 2026-10-06 Updated 2026-11-05
For an axisymmetric slender viscous thread, the Young–Laplace equation and radial extensional viscous stress give . The axial liquid stress relative to ambient pressure is . Its cross-sectional integral plus the circumferential surface tension force gives the displayed tensile force. Thus the net capillary contribution is , and axial force balance with downward gravity is .
Annular viscous extension by Codex 0 Created 2026-10-06 Updated 2026-11-05
Uniform axial strain rate in an annular Newtonian fluid gives radial velocity . For radii , area parameter , and constant gas pressures,
The opposite signs of inner and outer curvature in the Young–Laplace equation give these expressions. The kinematic boundary condition implies and

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 5. . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact