Hubbry Logo
GravitinoGravitinoMain
Open search
Gravitino
Community hub
Gravitino
logo
7 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Gravitino
Gravitino
Gravitino
View on Wikipedia
from Wikipedia
Gravitino
Compositionelementary particle
Statisticsfermionic
Familyfermion
Interactionsgravitation
Statushypothetical
SymbolG͂
Antiparticleself
Electric charge0 e
Spin⁠3/2⁠ ħ

In supergravity theories combining general relativity and supersymmetry, the gravitino (G͂) is the gauge fermion supersymmetric partner of the hypothesized graviton. It has been suggested as a candidate for dark matter.

If it exists, it is a fermion of spin ⁠3/2⁠ ħ and therefore obeys the Rarita–Schwinger equation. The gravitino field is conventionally written as ψμα with μ = 0, 1, 2, 3 a four-vector index and α = 1, 2 a spinor index. For μ = 0 one would get negative norm modes, as with every massless particle of spin 1 ħ or higher. These modes are unphysical, and for consistency there must be a gauge symmetry which cancels these modes: δψμα = ∂μεα, where εα(x) is a spinor function of spacetime. This gauge symmetry is a local supersymmetry transformation, and the resulting theory is supergravity.

Thus the gravitino is the fermion mediating supergravity interactions, just as the photon is mediating electromagnetism, and the graviton is presumably mediating gravitation. Whenever supersymmetry is broken in supergravity theories, it acquires a mass which is determined by the scale at which supersymmetry is broken. This varies greatly between different models of supersymmetry breaking, but if supersymmetry is to solve the hierarchy problem of the Standard Model, the gravitino cannot be more massive than about 1 TeV/c2.

History

[edit]

Murray Gell-Mann and Peter van Nieuwenhuizen intended the spin-3/2 particle associated with supergravity to be called the 'hemitrion', meaning 'half-3', however the editors of Physical Review were not keen on the name and instead suggested 'massless Rarita–Schwinger particle' for their 1977 publication.[1][2] The current name of gravitino was instead suggested by Sidney Coleman and Heinz Pagels,[3] although this term was originally coined in 1954 by Felix Pirani to describe a class of negative energy excitations with zero rest mass.[4]

Gravitino cosmological problem

[edit]

If the gravitino indeed has a mass of the order of 1 TeV/c2, then it creates a problem in the standard model of cosmology, at least naïvely.[5][6][7][8]

One option is that the gravitino is stable. This would be the case if the gravitino is the lightest supersymmetric particle and R-parity is conserved (or nearly so). In this case the gravitino is a candidate for dark matter; as such gravitinos will have been created in the very early universe. However, one may calculate the density of gravitinos and it turns out to be much higher than the observed dark matter density.

The other option is that the gravitino is unstable. Thus the gravitinos mentioned above would decay and will not contribute to the observed dark matter density. However, since they decay only through gravitational interactions, their lifetime would be very long, of the order of M 2
pl /m3, where Mpl is the Planck mass and m is the mass of a gravitino. For a gravitino mass of the order of 1 TeV/c2 this would be 105 s, much later than the era of nucleosynthesis. At least one possible channel of decay must include either a photon, a charged lepton or a meson, each of which would be energetic enough to destroy a nucleus if it strikes one. One can show that enough such energetic particles will be created in the decay as to destroy almost all the nuclei created in the era of nucleosynthesis, in contrast with observations. In fact, in such a case the universe would have been made of hydrogen alone, and star formation would probably be impossible.

One possible solution to the cosmological gravitino problem is the split supersymmetry model, where the gravitino mass is much higher than the TeV scale, but other fermionic supersymmetric partners of standard model particles already appear at this scale.

Another solution is that R-parity is slightly violated and the gravitino is the lightest supersymmetric particle. This causes almost all supersymmetric particles in the early Universe to decay into Standard Model particles via R-parity violating interactions well before the synthesis of primordial nuclei; a small fraction however decay into gravitinos, whose half-life is orders of magnitude greater than the age of the Universe due to the suppression of the decay rate by the Planck scale and the small R-parity violating couplings.[9]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Gravitino

View on Grokipedia
from Grokipedia
The gravitino (denoted as G~\tilde{G}) is a hypothetical spin-3/2 fermionic particle that acts as the superpartner of the graviton in supergravity theories, which incorporate local supersymmetry to unify gravity with the Standard Model of particle physics. Its mass, typically ranging from keV to TeV scales depending on the supersymmetry (SUSY) breaking mechanism—such as gravity mediation (TeV), anomaly mediation (100 TeV), or gauge mediation (keV–GeV)—arises from the spontaneous breaking of SUSY, and it interacts very weakly with matter via gravitational couplings suppressed by the Planck scale (MPl≈1.2×1019M_\mathrm{Pl} \approx 1.2 \times 10^{19} GeV). In models conserving R-parity, the gravitino is stable and often considered the lightest supersymmetric particle (LSP), making it a leading candidate for cold dark matter due to its relic abundance matching observations like those from the Planck satellite (ΩDMh2≈0.12\Omega_\mathrm{DM} h^2 \approx 0.12). In frameworks, the gravitino emerges as the gauge fermion associated with supersymmetry translations, distinguishing it from other superpartners by its universal coupling to the supercurrent of all matter fields. Production mechanisms include freeze-out during the early reheating phase, where the relic density scales as ΩG~h2∝(TR/1010 GeV)(100 GeV/mG~)(mg~/1 TeV)2\Omega_{\tilde{G}} h^2 \propto (T_R / 10^{10}~\mathrm{GeV}) (100~\mathrm{GeV}/m_{\tilde{G}}) (m_{\tilde{g}}/1~\mathrm{TeV})^2 with reheating temperature TRT_R and gluino mass mg~m_{\tilde{g}}, or non- production via decays of the next-to-lightest SUSY particle (NLSP), yielding ΩG~h2≈(mG~/mNLSP)ΩNLSPh2\Omega_{\tilde{G}} h^2 \approx (m_{\tilde{G}} / m_\mathrm{NLSP}) \Omega_\mathrm{NLSP} h^2. Notable scenarios feature different NLSPs: a NLSP leads to prompt missing energy at colliders but constrains (BBN) via hadronic decays; a stau (τ~\tilde{\tau}) NLSP produces long-lived charged tracks detectable at the LHC, with limits exceeding 400 GeV from recent LHC searches (as of 2024); a stau NLSP may catalyze excess 6^6Li production resolving the cosmological lithium problem; a stop (t~\tilde{t}) NLSP hadronizes into heavy baryons like Λt+\Lambda_t^+, fitting BBN discrepancies for mt~=400m_{\tilde{t}} = 400–600600 GeV and mG~=2m_{\tilde{G}} = 2–1010 GeV; while a sneutrino NLSP minimizes BBN impacts but requires low abundance (YνMν≲10−11Y_\nu M_\nu \lesssim 10^{-11} GeV). Cosmological constraints tightly bound gravitino parameters: thermal production limits TR≲109T_R \lesssim 10^9–101010^{10} GeV to avoid overclosing the or disrupting BBN, while late NLSP decays (lifetimes τ∼1\tau \sim 1 s for TeV-scale masses) must preserve light element abundances (e.g., 4^4He, D, 7^7Li) and distortions (μ≤9×10−5\mu \leq 9 \times 10^{-5}). At high-energy colliders like the LHC, gravitino signatures manifest as missing transverse energy from NLSP cascades, with prospects for indirect detection via gamma rays or neutrinos from annihilations remaining challenging due to suppressed couplings. As of 2025, studies explore ultra-heavy (EeV-scale) gravitinos as candidates for warm or solutions to problems, facing ongoing tensions with large-scale observations and new constraints from recent cosmological data. Ongoing analyses of 2025 cosmological observations continue to refine constraints on gravitino models, particularly their viability as . Overall, the gravitino's elusive nature underscores its role in probing SUSY beyond the , with ongoing experiments like those at the LHC potentially illuminating its phenomenology.

Theoretical Foundations

Definition in Supergravity

In theories, which extend by incorporating local , the gravitino emerges as the fundamental fermionic component of the supermultiplet. Specifically, in four-dimensional , the gravitino is a spin-3/2 particle that acts as the of the spin-2 . It is represented by a vector-spinor field ψμ\psi_\mu, a with a Lorentz vector index, subject to the Rarita-Schwinger constraint γμψμ=0\gamma^\mu \psi_\mu = 0 to eliminate lower-spin components and ensure the correct degrees of freedom for a massless spin-3/2 field. The dynamics of the gravitino are governed by the Lagrangian, which includes a kinetic term of the form −g ψˉμγμνρDνψρ\sqrt{-g} \, \bar{\psi}_\mu \gamma^{\mu\nu\rho} D_\nu \psi_\rho
Add your contribution
Related Hubs
User Avatar
No comments yet.