**Topics, Q**

*Q*-Balls

* __Idea__: Non-topological solitons
which exist classically for any fixed value of an unbroken global charge *Q*.

@ __References__: Kusenko PLB(97)
[small charge]; Graham PLB(01)ht [quantum effects, stability];
Deshaies-Jacques & MacKenzie PRD(06)ht [in Maxwell-Chern-Simons theory];
Tsumagari PhD(09)-a0910 [formation and stationary properties].

** Q-Glass** > see solid matter.

** Q-Manifold** > see manifolds [supermanifolds].

*q*-Metric

* __Idea__: The simplest generalization
of the Schwarzschild solution that contains a quadrupole parameter.

@ __References__: Toktarbay & Quevedo G&C(14)-a1510 [generalized to the stationary case].

**Q-Screen** > see thermodynamical laws [generalized second law].

*Q*-Stars

@ __References__: Prikas NPB(04) [in 2+1 dimensions], PLB(05) [in scalar-tensor theories].

**QBism** > s.a. probabilities in quantum theory [Bayesian approach].

* __Idea__: In general, the view that science is a tool that each of us can use to organize our own personal experience, and is thus about the subject (the user of science) and not just about the object (the world external to that user); Called QBism by Fuchs and Schack.

@ __Books__: von Baeyer 16, rev McQueen a1707.

@ __General references__: Fuchs a1003; Mermin PT(12)jul; Fuchs et al AJP(14)aug-a1311, comment Nauenberg AJP(15)mar-a1502, reply Fuchs et al a1502 [introduction, and locality]; Mermin a1312 [and classical mechanics]; Mermin nat(14)mar [intro]; Fuchs a1405 [history, long collection of letters and documents]; Mermin a1406 [clarification]; Mermin a1409-conf [what John Bell might have thought of it]; Mohrhoff a1409 [critical appraisal]; Stacey PTRS(16)-a1412 [John von Neumann was not a quantum Bayesian]; Fuchs & Schack PS(15)-a1412; Khrennikov a1412 [reflections by an external observer]; Fuchs a1601-in; Khrennikov a1604; Fuchs a1705 [reasons for QBism]; Bub a1711.

@ __Criticisms__: Marchildon FP(15)-a1403; Kupczynski a1505; Gründler a1606 [and non-locality]; Mohrhoff a1608.

**QCD** > s.a. QCD phenomenology.

**QED** > s.a. modified versions, in curved spacetime [including (quantum) gravity effects], and QED
phenomenology.

**Quadratic Curvature Terms** > see higher-order gravity.

**Quadratic Equation** > see elementary algebra.

**Quadratic Form / Function** > s.a.
Bilinear Form.

$ __Def__: A quadratic form
on a vector space *V* is a function *f* : *V* → \(\mathbb R\) that
can be written as *f*(*v*) = ∑_{i}
*l*_{i}(*v*) *l*_{i}'(*v*),
where *l*_{i} and *l*_{i}'
are linear for all *i*.

* __Relationships__: Any
quadratic form defines a positive-definite bilinear form.

* __Sesquilinear form__: A quadratic form on a complex vector space, which
is linear in one argument and anti-linear in the other; Used to define (complex) Hilbert spaces.

@ __References__: O'Meara 63; Coll & Morales JMP(93) [signature].

**Quadrilateralland** > see Relational Theories.

**Quadrupole Formula for Gravitational-Radiation Energy Loss** > s.a. gravitational
radiation / brane
phenomenology; multipoles.

* __Assumptions__: Velocities
are small, and *T*_{00} dominates the
stress-energy tensor; The approximation ignores the internal structure of the
star and orbiting particle, and is valid in the large-distance limit.

* __Formula__:

–d*E*/d*t* = ∑_{i,
j =
1}^{3} (*G*/45*c*^{5})(d^{3}*Q*_{ij }/d*t*^{3})^{2}, *Q*_{ij} = ∫ d^{3}*x* *μ*(**x**)
(3 *x*_{i }*x*_{j }– δ_{ij}* r*^{2})
.

@ __References__: in Misner et al 73; Ehlers et al ApJ(76)
[controversy]; Walker & Will PRL(80);
in Wald 84; Winicour GRG(87);
Helfer PRD(93); Ashtekar et al PRD(15)-a1510 [with a positive cosmological constant].

**Quality Factor Q** > see oscillator.

**Quantions**

* __Idea__: A non-division
algebra; Similarly to quaternions, quantions preserve the core features of
associativity and complex conjugation, while giving up the notion of division;
They have been used as a framework for electroweak theory on curved spacetime.

@ __References__: Moldoveanu a0901
[and unification of quantum mechanics and relativity].

**Quantization**

> __General frameworks__: see quantum mechanics; quantum field theory; Third Quantization.

> __ Operator-based approaches__: see canonical quantization; quantum formalism; geometric quantization; representations; stochastic quantization.

> __Histories-based approaches__: see histories quantum theory; path integral quantization.

> __Modified approaches__: see deformed quantum theory; modified quantum theory; relativistic quantum theory.

**Quantropy**

@ __References__: Baez & Pollard Ent(15)-a1311.

**Quantum Action Principle** > see renormalization [algebraic]; Schwinger's Variational Principle.

**Quantum Algebra** > s.a. quantum
group.

@ __References__: Pillin CMP(96)
[deformed Heisenberg algebra]; Jaganathan mp/00-intro, mp/01-proc;
Celeghini &
del Olmo EPL(03)ht/01 [and
quantum theory]; Banica & Collins JGP(08)
[Pauli representation of quantum permutation algebra].

**Quantum Billiard** > see spectral
geometry.

**Quantum Carpet**

* __Idea__: A generic spacetime
pattern formed in the probability distributions *P*(*x*, *t*)
of 1D
quantum particles, first discovered in 1995; It is related to the Talbot Effect
and to quantum state revivals.

@ __References__: Hall et al JPA(99)qp [and
travelling waves]; Friesch et al NJP(00);
Berry et al pw(01)jun.

**Quantum Cosmology** > s.a. FLRW quantum cosmology.

**Quantum Darwinism** > see decoherence.

**Quantum Deformation** > see deformation
quantization; differential geometry; hamiltonian
dynamics; quantum particle models.

**Quantum Dot** > see quantum technology.

**Quantum Eraser** > see under Erasure.

**Quantum Field Theory** > s.a. approaches;
effective theories; effects;
states; types of theories.

**Quantum Field Theory in Curved Spacetime**
> s.a. various backgrounds and effects.

**Quantum Graphity** > see discrete geometry models / computation [universe as computer].

**Quantum Gravity** > s.a. 2D;
3D; approaches;
canonical; matter
phenomenology; semiclassical quantum gravity; ...

**Quantum Interest** > see quantum field theory effects.

**Quantum Jump / Transition** > see quantum states.

**Quantum Logic** > see logic.

**Quantum Maps**

@ __References__: Milz et al a1708.

**Quantum Mechanics** > s.a. effects;
experiments;
formulations; histories;
interpretations;
semiclassical; states;
systems; ...

**Quantumness (Degree of Non-Classicality)** > see classical limit of quantum theory;
correlations.

**Quantum Non-Demolition Experiments** > see experiments
in quantum mechanics; Non-Demolition Principle.

**Quantum Optics** > see optics.

**Quantum Potential** > see pilot-wave interpretation.

**Quantum Protectorate** > see composite quantum systems.

**Quantum Revival** > see quantum states.

**Quantum Spacetime** > s.a. proposals.

**Quantum States** [including revivals].

**Quark** > see hadrons;
QCD phenomenology [including quark-gluon plasma].

**Quark Nugget** > see QCD effects / dark matter
types; early-universe baryogenesis.

**Quark Star** > see astronomical objects.

**Quarkonium**

* __Idea__: Bound states
of a heavy quark *Q* = *c*, *b* and the corresponding
antiquark.

@ __References__: Eichten et al RMP(08) [rev].

> __Online resources__: see Wikipedia page.

**Quartic Equation** > see elementary
algebra.

**Quasicondensation** > see quantum phase transitions.

**Quasifold**

* __Idea__: A space locally
modelled on \(\mathbb R\)* ^{k}* modulo the action of a discrete, possibly
infinite,
group.

**Quasilocal Formulation of Field Theory** > see quasilocal formulation of general
relativity; quasilocal mass / reference frames.

**Quasinormal Modes** > see black-hole perturbations.

**Quasiorder** > s.a. Preorder.

$ __Def__: A transitive relation.

* __Relationships__: A finite
quasiordered set is the same as a finite topological space (> see poset).

* __Example__: The refinement
relation between covers of a topological space is a reflexive quasiorder (a preorder or
*direction*), but it is not antisymmetric.

@ __General references__: in Isbell 64, p3.

@ __Related topics__: Ding DM(09) [canonical antichains].

**Quasiparticle** > s.a. particle
types; Hole; Orbiton; Phonon;
Polaron; Roton.

* __Idea__: A composite object
produced when one "immerses" a particle in a quantum many-body system, for
instance an electron in a solid; The particle "swims" shrouded
by a cloud of excitations of its new environment, which modifies its physical
properties (mass, charge, etc.); The most famous example is a "hole".

* __Polariton__: A mixed photonic and electronic excitation; > s.a. black-hole analogs; bose-einstein condensation; photon phenomenology.

@ __Bogoliubov quasiparticles__: Zhang et al PRL(06)cm/05,
Horváth et al cm/05 [in
a superfluid].

@ __Polaritons__: Karzig et al PRX(15) [topological polaritons]; Ohadi et al PRX(15) [polariton condensates and their uses]; > s.a. bose-einstein
condensates.

@ __Other types__: Schirotzek et al PRL(09)
+ Chevy Phy(09)
[fermionic analog of a solid-state polaron]; Soluyanov Phy(17) [type-II Dirac fermions].

> __Online resources__: see Wikipedia page.

**Quasiperiodic Function** > not to be confused with an Almost Periodic Function.

* __Idea__: A function of the form

*f*(*x*) = ∑_{j=1}^{n}* c*_{j} exp{i *k*_{j}*x*}
,

for some integer *n* and real numbers *c*_{j}, *k*_{j}; They form an algebra and
can be endowed with the sup norm, and is naturally isomorphic to the algebra
of continuous functions on the Bohr compactification of \(\mathbb R\).

* __In dynamical systems__: Many dynamical systems are a complex mix of chaotic and quasiperiodic behaviors, and chaotic trajectories near quasiperiodic points can have long near-quasiperiodic transients.

@ __References__: Das et al EPL(16)-a1512 [computational technique for analyzing quasiperiodicity and distinguishing it from chaos].

> __Online resources__: see Wikipedia page.

**Quasiperiodic Tiling** > see crystals [quasicrystals];
tilings.

**Quasiprobabilities** > see probability in quantum theory.

**Quasiset Theory** > s.a. locality.

* __Idea__: The mathematical
theory of collections of indistinguishable objects

@ __General references__:
Sant'Anna qp/04 [and undecidable finite sets].

@ __And identical particles__: Sant'Anna qp/98,
& Santos FP(00)qp/99;
Sant'Anna FPL(05)qp/04;
Domenech & Holik FP(07)-a0705;
Domenech et al FP(08)-a0803.

> __Online resources__:
see Wikipedia page.

**Quasispherical Metric** > see types of metrics.

**Quasi-Topological Gravity** > see black holes in modified theories;
gravitational thermodynamics.

**Quasitopological Group** > see Topological Group.

**Qubit, Qudit** > see discrete quantum systems.

**Quillen Determinant**

@ __References__: Furutani JGP(04) [line bundle].

**Quintic Equation** > see elementary algebra.

**Quintom Dark Energy**

* __Idea__: A hybrid of quintessence
and phantom dark energy which involves the participation of two real scalar
fields playing the roles of those two types of dark energy.

@ __Cosmology__: Lazkoz & León PLB(06);
Cai et al PRP(10).

**Quipper** > see quantum computing.

**Quirky Matter** > see types of dark matter.

**Quiver Gauge Theory** > s.a. particle physics.

@ __References__: Szabo & Valdivia JHEP(14)-a1404 [covariant].

**Quiver Varieties**

@ __References__: Ginzburg m.QA/00.

**Quons** > see particle statistics.

**Quotient Function**

$ __Def__: The function *Q*(*x*):=
(1–*x*)/(1+*x*).

@ __References__: Lindell & Sihvola AJP(98)mar [applications].

**Qutrit** > see quantum systems; entanglement; black-hole entropy.

main page
– abbreviations
– journals – comments
– other sites – acknowledgements

send feedback and suggestions to bombelli at olemiss.edu – modified 20 feb 2018