The Cosmological-Constant Problem| The Cosmological-Constant Problem |
In General
> s.a. boundaries in field theory; branes;
quintessence; vacuum.
* Idea: The current formulation
of the problem is, Why is the observed value of the cosmological constant so small
(e.g., after so many phase transitions)? [Before 1997-1998, the question usually
was, Why is its observed value zero?]
* Second problem: The coincidence
between the epoch of galaxy formation tgal
and the epoch of Λ-domination tcc;
> s.a. Coincidence Problem.
@ Reviews: Adler et al AJP(95)jul;
Dolgov ap/97-proc;
Weinberg ap/00-conf;
Straumann ap/00-conf,
ap/02-conf,
gq/02-conf;
Brax CP(04);
Banks PT(04)mar;
Nobbenhuis PhD(06)gq [approaches];
Solà JPCS(13)-a1306 [pedagogical];
Burgess a1309-ln [the naturalness problem and microphysics];
Padilla a1502-ln;
Ng a1706-proc [approaches].
@ And the equivalence principle: Bertolami IJMPD(09) [violation]; Ginat a2105-GRF [the equivalence principle helps].
Higher-Dimensional Proposed Solutions
* Idea: Many proposals
have been made; 2000, recent ones include large extra dimensions
(> see brane cosmology).
@ Strings / M-theory: Witten MPLA(95)ht,
Kane et al PLB(05) [string vacua];
McGuigan ht/06,
ht/06 [seesaw];
Hawking & Hertog PRD(06)
+ pn(06)jun;
de Alwis PLB(07)ht/06;
Bousso ht/06-talk [local values and the landscape];
Barvinsky PRL(07);
Kiefer et al CQG(11)-a1010 [landscape-motivated];
Avilán & Roldán a1011;
Bousso a1203-proc [and the string theory landscape];
Sumitomo & Tye JCAP(12)-a1204 [simple stringy mechanism];
> s.a. string phenomenology.
@ Brane world:
Burgess et al PLB(00);
Förste et al JHEP(00);
Chen et al JHEP(00);
Arkani-Hamed et al PLB(00)ht;
Kakushadze PLB(00)ht,
PLB(00)ht,
PLB(00)ht;
de Alwis NPB(01);
Flanagan et al PRD(01) [and hierarchy];
Tye & Wasserman PRL(01);
Nojiri et al RMF(02)ht/01;
Corradini et al MPLA(03),
IJMPA(03)ht/02;
Sorkin BJP(05)gq-proc [the value of Λ would be too small];
Ellwanger MPLA(05);
Steinhard & Turok Sci(06)ap
+ pw(06)may
[cyclic universe with decreasing cosmological constant],
comment Vilenkin Sci(06)ap;
Diakonos & Saridakis JCAP(09)-a0708;
Shao & Chen PRD(10)-a1005.
@ Other higher-dimensional: Wesson & Liu IJMPD(01)gq [Kaluza-Klein theory];
Erdem JPA(07)gq/06-conf,
JPA(08)-a0712 [symmetries];
Hertzberg & Masoumi JCAP(16)-a1509.
Quantum Gravity and Modified-Gravity Solutions
> s.a. modified general relativity; time in quantum theory.
* Conformal gravity: The
theory naturally quenches the amount by which the cosmological constant
gravitates, rather than its value.
@ Quantum cosmology: Hawking PLB(84);
Weiss PLB(87),
Duff PLB(89) [criticism];
Wu PLB(08)-a0709;
Shaw & Barrow PRD(11)-a1010 [value depends on observation time];
Larsen et al PRD(11)-a1107 [in the quantum multiverse];
Jalalzadeh et al PDU-a1709 [q-deformed];
> s.a. quantum gravity phenomenology [including wormholes, baby universes].
@ Lattice-type approaches:
Vergeles ht/04 [lattice quantum gravity];
Loll et al NPB(06) [2D causal, with topology change].
@ And discrete spacetime: Mok ap/01;
Trout a1208,
a1208;
Miković & Vojinović EPL(15)-a1407 [quantum Regge calculus approach].
@ Other quantum gravity: Özer NPB(91) [third quantization];
Alexander & Calcagni PLB(09)-a0806 [superconducting lqg];
Mannheim MPLA(11)-a1005-conf [intrinsically quantum-mechanical gravity];
Miao & Zhao IJMPD(14)-a1312 [and gup];
Moffat a1407-proc [finite, unitary non-local formulation];
Carlip PRL(19)-a1809,
comment Wang & Unruh a1911,
reply Carlip a1911,
comment Piattella a2007
[high curvature at Planck scales, hidden at observable scales];
Hogan a2003
[gravitational drag from coherent energy flows];
> s.a. approaches to quantum gravity [gravity
as condensate]; non-commutative cosmology.
@ Related proposals:
Linde PLB(88) [two universes];
Özer gq/00
[from gravity + electromagnetism unification];
Sundrum PRD(04)ht/03 [fat gravitons];
Alexander et al ht/04 [vacuum gravitational instability];
Novello PoS-ap/05 [and graviton mass];
Prokopec gq/06 [semiclassical general relativity + matter];
Nojiri et al PLB(11)-a1010 [non-local gravity];
García-Aspeitia a1011 [2D spacetime and Planck scale];
Aslanbeigi et al PRD(11)-a1106,
Wondrak a1705-conf [gravitational aether];
Wilson JModP(13)-a1111;
Finazzi et al PRL(12)
+ news at(12)feb,
PhysOrg(12)mar [analog gravity and BECs];
Mannheim a1703-GRF
[fully quantum-mechanically consistent conformal gravity];
Carroll & Remmen PRD(17)-a1703 [non-local constraint on the action];
Vasak et al a1802 [covariant canonical gauge theory of gravity];
Xiong a1805;
Appleby & Linder a2009 [well tempering];
> s.a. Übergravity.
Other Proposed Solutions > s.a. cosmological constant
[scale dependence, variation, etc]; particle statistics [quons].
* Remark: Supersymmetry doesn't help, it is broken!
@ From vacuum fluctuations: Gurzadyan & Xue MPLA(03)ap/01,
ap/05;
Padmanabhan CQG(05)ht/04;
Qi ht/05 [QED];
Samuel & Sinha PRL(06)cm [surface tension analog];
Beck & Mackey PhyA(07)ap/06 [measurability];
Doran & Jaeckel JCAP(06)ap [and measurements];
Maggiore PRD(11);
Wang et al PRD(17)-a1703 [gravitating vacuum energy];
Wetterich PLB(17)-a1704 [graviton fluctuations];
Pejhan et al PLB(18)-a1808 [from the Krein-Gupta-Bleuler vacuum];
Brax & Valageas a1903 [cancellation mechanism];
Carlip a1905-GRF [hidden by spacetime foam];
Bengochea et al a1906 [problematic];
Viaggiu FP-a1910 [and metric averaging procedure];
Leonhardt a2001 [in Lifshitz theory];
Lozano & Mazzitelli a2008 [oscillating universe from random fluctuations].
@ Supersymmetric: Jejjala et al GRG(03)ht-GRF [holography and supersymmetry];
Froggatt et al NPB(06) [supergravity models].
@ And holography: Arzano et al PLB(07)gq/06;
Carneiro IJMPD(03)gq-GRF;
> s.a. holography.
@ Other fields:
Barr et al PRD(06) [cancellation by cosmon];
Klinkhamer & Volovik JETPL(10)-a0907 [extension of standard model];
Popławski AdP(11)-a1105 [quarks and torsion];
Emelyanov & Klinkhamer PRD(12)-a1107,
PRD(12)-a1109,
Klinkhamer PRD(12) [two massless vector fields];
Padmanabhan & Padmanabhan IJMPD(13)-a1302 [inflation and particle physics parameters];
Nojiri MPLA(16)-a1601 [topological field theory];
Ahluwalia a2008 [spin-1/2 boson].
@ Other proposals:
Duncan & Jensen NPB(90) [4-form dynamics];
Ghoroku CQG(91);
Ng IJMPD(92);
Squires PLA(92);
Sivaram MPLA(99) [early-universe phase transition];
Nobbenhuis FP(06)gq/04;
Jackiw et al PLA(05)ht [λφ4 field in AdS];
Triay IJMPD(05)gq;
Nishino & Rajpoot MPLA(06) [Hodge duality];
Freese et al PLB(06) [devaluation];
't Hooft & Nobbenhuis CQG(06)gq [complex transformations];
Shapiro & Solà JPA(07)gq/06-conf;
Comelli IJMPA(08)-a0704 [modified Lagrangian];
O'Connell PLA(07) [causality-based];
Rodrigo CQG(07)-a0705 [void bubbles];
Andrianov et al PLB(07) [and spontaneous symmetry breaking];
Urban & Zhitnitsky JCAP(09)-a0906 [standard-model physics];
Linde & Vanchurin a1011 ["non-anthropic"];
Koksma & Prokopec a1105 [Lorentz invariance of the vacuum];
Maia IJMPcs(11)-a1107-talk [and spacetime deformation];
Darabi a1107;
Astashenok & Del Popolo CQG(12)-a1203 [with volume averaging];
Jain et al IJMPA(15)-a1408 [conformal symmetry breaking];
Kourkoulou et al a2101 [non-trivial cancellations, analog model].
Other Proposed Solutions > s.a. dynamical
wave-function collapse; Topos Theory.
* Anthropic approach:
There is a probability distribution of values of the cosmological constant
in different regions, and we live in one that is conducive to life.
@ Anthropic approach:
in Barrow & Tipler 86, ch6;
Weinberg PRL(87);
Efstathiou MNRAS(95);
Garriga et al PRD(00)ap/99;
Donoghue JHEP(00);
Förste et al PLB(00)gq;
Garriga & Vilenkin PRD(00)ap/99,
PRD(01)ht/00;
Barrow et al PRD(02)ap/01;
Banks et al JHEP(01);
Vilenkin in(03)ht/01;
Graesser et al PLB(04)ht;
Garriga & Vilenkin PTPS(06)ht/05;
Loeb JCAP(06)ap [observational test];
Starkman & Trotta PRL(06)ap,
Trotta & Starkman AIP(06)ap [against];
Pogosian & Vilenkin JCAP(07)ap/06 [and WMAP-3 data];
Bousso et al PRD(07)ht [causal entropic principle];
Miralda-Escudé ap/07 [stryngbohtyk model];
Peacock MNRAS(07)-a0705;
Olum & Schwartz-Perlov JCAP(07)-a0705 [in a large toy landscape];
Maor et al PRL(08)-a0709 [criticism];
Mersini-Houghton & Adams CQG(08)-a0810 [limitations];
Maia & Capistrano IJMPA(09)-a0905;
Iorio MNRAS(10)-a0911 [the Sun's motion through the Milky Way];
Hong et al PRD(12)-a1110 [and primordial density perturbations];
Hartle & Hertog PRD(13)-a1309 [anthropic bounds from the no-boundary quantum state];
Berolami & Páramos GRG(20) [non-minimally coupled].
@ No zero-point energy contributions: Kimpton & Padilla JHEP(12)-a1112;
Bernard & LeClair PRD(13)-a1211;
Kaloper & Padilla PRL(14)-a1309,
PRD(104)-a1406 [sequestering];
Fujii a1403;
Balitsky & Kiselev PRD(14)-a1406 [vacuum energy suppression];
Barrow & Cotsakis a1907 [traceless f(R) gravity];
Yargic et al PRD-a2001
[only part of the stress-energy tensor gravitates];
Donoghue a2009 [in perturbation theory];
> s.a. canonical quantization [covariant].
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