Scalars, vectors and tensors from metric-affine gravity

Karahan, Canan; Altaş, Aslı; Demir, Durmuş A.

doi:10.1007/s10714-012-1473-x

Cited by 22 publications

(26 citation statements)

References 63 publications

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“…Second, it couples only to fermions f ⊂ . And its couplings, originating from the spin connection through the decomposition in (11), are necessarily flavor-universal. It couples to the known (leptons and quarks in the SM) and any hypothetical (say, the dark matter particle χ) fermion in the same way, with the same strength.…”

Section: Metric-affine Gravitymentioning

confidence: 99%

Geometric dark matter

Demir

Puliçe

2020

J. Cosmol. Astropart. Phys.

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The dark matter, needed for various phenomena ranging from flat rotation curves to structure formation, seems to be not only neutral and long-living but also highly secluded from the ordinary matter. Here we show that, metric-affine gravity, which involves metric tensor and affine connection as two independent fields, dynamically reduces, in its minimal form, to the usual gravity plus a massive vector field. The vector Y µ , which interacts with only the quarks, leptons and gravity, is neutral and long-living (longer than the age of the Universe) when its mass range lies in the range 9.4 MeV < M Y < 28.4 MeV. Its scattering cross section from nucleons, which is some 60 orders of magnitude below the current bounds, is too small to facilitate direct detection of the dark matter. This property provides an explanation for whys and hows of dark matter searches. We show that due to its geometrical origin the Y µ does not couple to scalars and gauge bosons. It couples only to fermions. This very feature of the Y µ makes it fundamentally different than all the other vector dark matter candidates in the literature. The geometrical dark matter we present is minimal and self-consistent not only theoretically but also astrophysically in that its feebly interacting nature is all that is needed for its longevity. * Dedicated to the memory of Rahmi Güven, a great physicist and a candid friend.

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Section: Metric-affine Gravitymentioning

confidence: 99%

Geometric dark matter

Demir

Puliçe

2020

J. Cosmol. Astropart. Phys.

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“…• In obtaining the MOND equation of motion (25) we have neglected contributions from the spatial variation of ρ. The situation can be improved by incorporating such terms from (24).…”

Section: Conclusion and Future Prospectsmentioning

confidence: 99%

“…In the first, after setting a = −∇φ g with φ g being the gravitational potential, one formulates MOND as a modification in gravitational laws (see the reviews [15][16][17]). In this case, one is necessarily led to modified Newtonian gravity [18,19] or General Relativity (GR) extended by geometrical scalar and vector fields [20][21][22][23][24][25]. Besides, there are alternative approaches based on f (R) gravity [26][27][28][29], bimetric gravity [30,31], time foliation [32,33], nonlocal metric theories [34,35], Galileons [36], and Horava-Lifshitz gravity [37].…”

Section: Introductionmentioning

confidence: 99%

Relativistic MOND from modified energetics

Demir

Karahan

2014

Eur. Phys. J. C

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We begin to investigate the question of what modifications in the energy-momentum tensor can yield the correct MOND regime. As a starting study, we refrain from insisting on an action principle and focus exclusively on the equations of motion. The present work, despite the absence of an explicit action functional, can be regarded to extend Milgrom's modified inertia approach to relativistic domain. Our results show that a proper MOND limit arises if the energymomentum tensor is modified to involve the determinant of the metric tensor in reference to the flat metric, where the latter is dynamically generated as in the gravitational Higgs mechanism. This modified energy-momentum tensor is conserved in both Newtonian and MONDian regimes.

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“…It was suggested that a matter-antimatter asymmetry generated by the Hehl-Datta cubic term [11] in the Dirac equation modified by the presence of torsion, could be at the origin of the presence of dark matter in the universe [12]. The decomposition of a metric-affine theory in scalars, vectors and tensors contribution, in a way to match the results of TeVeS phenomenology, was analyzed in [13]. The authors of [14], instead, suggested to fit Supernovae data replacing the dark matter content expected as from the ΛCDM model with a mean spin density of baryonic matter.…”

Section: Introductionmentioning

confidence: 99%

The role of nonmetricity in metric-affine theories of gravity

Vitagliano¹

2014

Class. Quantum Grav.

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The intriguing choice to treat alternative theories of gravity by means of the Palatini approach, namely elevating the affine connection to the role of independent variable, contains the seed of some interesting (usually under-explored) generalizations of General Relativity, the metric-affine theories of gravity. The peculiar aspect of these theories is to provide a natural way for matter fields to be coupled to the independent connection through the covariant derivative built from the connection itself. Adopting a procedure borrowed from the effective field theory prescriptions, we study the dynamics of metric-affine theories of increasing order, that in the complete version include invariants built from curvature, nonmetricity and torsion. We show that even including terms obtained from nonmetricity and torsion to the second order density Lagrangian, the connection lacks dynamics and acts as an auxiliary field that can be algebraically eliminated, resulting in some extra interactions between metric and matter fields.Dedicated to the memory of Francesco Caracciolo

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Scalars, vectors and tensors from metric-affine gravity

Cited by 22 publications

References 63 publications

Geometric dark matter

Geometric dark matter

Relativistic MOND from modified energetics

The role of nonmetricity in metric-affine theories of gravity

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