66 research outputs found
Cotton gravity and 84 galaxy rotation curves
Recently, as a generalization of general relativity, a gravity theory has
been proposed in which gravitational field equations are described by the
Cotton tensor. That theory allows an additional contribution to the
gravitational potential of a point mass that rises linearly with radius as
, where is the Newton constant. The coefficients
and are the constants of integration and should be determined
individually for each physical system. When applied to galaxies, the
coefficient , which has the dimension of acceleration, should be
determined for each galaxy. This is the same as having to determine the mass
for each galaxy. If is small enough, the linear potential term is
negligible at short distances, but can become significant at large distances.
In fact, it may contribute to the extragalactic systems. In this paper, we
derive the effective field equation for Cotton gravity applicable to
extragalactic systems. We then use the effective field equation to numerically
compute the gravitational potential of a sample of 84 rotating galaxies. The 84
galaxies span a wide range, from stellar disk-dominated spirals to
gas-dominated dwarf galaxies. We do not assume the radial density profile of
the stellar disk, bulge, or gas; we use only the observed data. We find that
the rotation curves of 84 galaxies can be explained by the observed
distribution of baryons. This is due to the flexibility of Cotton gravity to
allow the integration constant for each galaxy. In the context of
Cotton gravity, "dark matter" is in some sense automatically included as a
curvature of spacetime. Consequently, even galaxies that have been assumed to
be dominated by dark matter do not need dark matter.Comment: 22 pages, 7 figures, 1 table, accepted for publication in Phys. Rev.
D, v2: published versio
Dark energy in conformal Killing gravity
The Friedmann equation, enriched by an additional term that effectively takes
on the role of specific dark energy, is demonstrated to serve as an exact
solution within the recently proposed gravitational theory named "conformal
Killing gravity". This theory does not explicitly incorporate dark energy. This
finding suggests that there's no necessity to postulate the existence of dark
energy as an independent physical entity. The dark energy effectively arising
from this theory is characterized by a specific equation of state parameter,
denoted as , which is uniquely determined to be , classifying it
as phantom energy. If this effective dark energy is present in a moderate
amount, typically around 5\% of the total energy density at the present time,
and under the assumption of density parameters for matter and the cosmological
constant, and ,
respectively, the expansion of the universe at low redshifts () can
exceed expectations, while the expansion at remains unchanged. This
holds the potential to address the Hubble tension problem.Comment: 6 pages, 2 figure
Gravity at cosmological distances: Explaining the accelerating expansion without dark energy
Three theoretical criteria for gravitational theories beyond general
relativity are considered: obtaining the cosmological constant as an
integration constant, deriving the energy conservation law as a consequence of
the field equations, rather than assuming it, and not necessarily considering
conformally flat metrics as vacuum solutions. Existing theories, including
general relativity, do not simultaneously fulfill all three criteria. To
address this, a new gravitational field equation is proposed that satisfies
these criteria. From this equation, a spherically symmetric exact solution is
derived, which is a generalization of the Schwarzschild solution. It
incorporates three terms: the Schwarzschild term, the de Sitter term, and a
newly discovered term, which is proportional to in a radial coordinate,
that becomes significant only at large distances. The equation is further
applied to cosmology, deriving an equation for the scale factor. It then
presents a solution that describes the transition from decelerating to
accelerating expansion in a matter-dominated universe. This is achieved without
the need for negative pressure as dark energy or the positive cosmological
constant. This provides a novel explanation for the current accelerating
expansion of the universe.Comment: 7 pages, 1 figure; accepted for publication in Phys.Rev.
Non-maximal \theta_{23}, large \theta_{13} and tri-bimaximal \theta_{12} via quark-lepton complementarity at next-to-leading order
We show that the next-to-leading order corrections in the quark-lepton
complementarity are important to explain the observed pattern of neutrino
mixing. In particular, the next-to-leading order corrections 1) lead to a
deviation of \theta_{23} from maximal mixing, 2) reduce the predicted value of
by 9.8%, 3) provide the same value of as that of the tri-bimaximal mixing. This is shown by calculating
to in the framework in
which the product of the CKM and PMNS matrices is bimaximal.Comment: 14 pages, 3 figures, a version to appear in EP
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