Classical and quantum ghosts

Sbisà, Fulvio

doi:10.1088/0143-0807/36/1/015009

Cited by 85 publications

(87 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As explained in Ref. [39], only modes with positive energy are able to decouple, but not a ghost state since there is no positive energy necessary to excite a ghost (see also Ref. [40]).…”

Section: Consequences Of the Existence Of Ghostsmentioning

confidence: 97%

Higuchi ghosts and gradient instabilities in bimetric gravity

Könnig

2015

Phys. Rev. D

View full text Add to dashboard Cite

Bimetric gravity theories allow for many different types of cosmological solutions, but not all of them are theoretically allowed. In this work we discuss the conditions to satisfy the Higuchi bound and to avoid gradient instabilities in the scalar sector at the linear level. We find that in expanding universes the ratio of the scale factors of the reference and observable metric has to increase at all times. This automatically implies a ghost-free helicity-2 and helicity-0 sector and enforces a phantom dark energy. Furthermore, the condition for the absence of gradient instabilities in the scalar sector will be analyzed. Finally, we discuss whether cosmological solutions can exist, including exotic evolutions like bouncing cosmologies, in which both the Higuchi ghost and scalar instabilities are absent at all times.

show abstract

“…As explained in Ref. [39], only modes with positive energy are able to decouple, but not a ghost state since there is no positive energy necessary to excite a ghost (see also Ref. [40]).…”

Section: Consequences Of the Existence Of Ghostsmentioning

confidence: 97%

Higuchi ghosts and gradient instabilities in bimetric gravity

Könnig

2015

Phys. Rev. D

View full text Add to dashboard Cite

show abstract

“…In the present study, we may infer that the DM particles undergo elastic scattering with scalar fields having negative kinetic term. It is well known that these fields suffer from instabilities at the classical and quantum levels [54,55] that casts doubts about their existence. Nevertheless, observationally such fields cannot be discarded, as we have also observed here.…”

Section: Resultsmentioning

confidence: 99%

Observational constraints on dark matter–dark energy scattering cross section

Kumar

Nunes

2017

Eur. Phys. J. C

View full text Add to dashboard Cite

In this letter, we report precise and robust observational constraints on the dark matter-dark energy scattering cross section, using the latest data from cosmic microwave background (CMB) Planck temperature and polarization, baryon acoustic oscillations (BAO) measurements and weak gravitational lensing data from CanadaFrance-Hawaii Telescope Lensing Survey (CFHTLenS). The scattering scenario consists of a pure momentum exchange between the dark components, and we find σ d < 10 −29 cm 2 (m dm c 2 /Gev) at 95% CL from the joint analysis (CMB + BAO + CFHTLenS), where m dm is a typical dark matter particle mass. We notice that the scattering among the dark components may influence the growth of large scale structure in the Universe, leaving the background cosmology unaltered.

show abstract

“…And, even worse, this decay will practically happen instantaneously (see refs. [10,11] for more details). Such a theory cannot describe a stable vacuum and therefore has to be ruled out.…”

Section: Jhep11(2016)118mentioning

confidence: 99%

“…However, we are interested in the case in which the phase-space density of ghosts is negligible. 6 Even though a (non-tachyonic) ghost is usually recognized as a field with negative kinetic energy, its mass term does also carry an additional minus sign [11]. Since eq.…”

Section: Ghost Decaymentioning

confidence: 99%

A spectre is haunting the cosmos: quantum stability of massive gravity with ghosts

Könnig

Nersisyan

Akrami

et al. 2016

J. High Energ. Phys.

View full text Add to dashboard Cite

Many theories of modified gravity with higher order derivatives are usually ignored because of serious problems that appear due to an additional ghost degree of freedom. Most dangerously, it causes an immediate decay of the vacuum. However, breaking Lorentz invariance can cure such abominable behavior. By analyzing a model that describes a massive graviton together with a remaining Boulware-Deser ghost mode we show that even ghostly theories of modified gravity can yield models that are viable at both classical and quantum levels and, therefore, they should not generally be ruled out. Furthermore, we identify the most dangerous quantum scattering process that has the main impact on the decay time and find differences to simple theories that only describe an ordinary scalar field and a ghost. Additionally, constraints on the parameters of the theory including some upper bounds on the Lorentz-breaking cutoff scale are presented. In particular, for a simple theory of massive gravity we find that a breaking of Lorentz invariance is allowed to happen even at scales above the Planck mass. Finally, we discuss the relevance to other theories of modified gravity.

show abstract

Classical and quantum ghosts

Cited by 85 publications

References 22 publications

Higuchi ghosts and gradient instabilities in bimetric gravity

Higuchi ghosts and gradient instabilities in bimetric gravity

Observational constraints on dark matter–dark energy scattering cross section

A spectre is haunting the cosmos: quantum stability of massive gravity with ghosts

Contact Info

Product

Resources

About