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Constraint on energy-momentum squared gravity from neutron stars and its cosmological implications
Deviations from the predictions of general relativity due to energy-momentum squared gravity (EMSG) are expected to become pronounced in the high density cores of neutron stars. We derive the hydrostatic equilibrium equations in EMSG and solve them numerically to obtain the neutron star mass-radius relations for four different realistic equations of state. We use the existing observational measurements of the masses and radii of neutron stars to constrain the free parameter, alpha; that
characterizes the coupling between matter and spacetime in EMSG.STF
Weak field and slow motion limits in energy-momentum powered gravity
We explore the weak field and slow motion limits, Newtonian and
Post-Newtonian limits, of the energy-momentum powered gravity (EMPG), viz., the
energy-momentum squared gravity (EMSG) of the form
with
and being constants. We have shown that EMPG with and
general relativity (GR) are not distinguishable by local tests, say, the Solar
System tests; as they lead to the same gravitational potential form, PPN
parameters, and geodesics for the test particles. However, within the EMPG
framework, , the mass of an astrophysical object inferred from
astronomical observations such as planetary orbits and deflection of light,
corresponds to the effective mass , being the actual physical mass and
being the modification due to EMPG. Accordingly, while in GR we simply have the
relation , in EMPG we have . Within
the framework of EMPG, if there is information about the values of
pair or from other independent phenomena (from
cosmological observations, structure of the astrophysical object, etc.), then
in principle it is possible to infer not only alone from
astronomical observations, but and separately. For a proper
analysis within EMPG framework, it is necessary to describe the slow motion
condition (also related to the Newtonian limit approximation) by (where and ), whereas this condition leads to in
GR.Comment: 12 pages, no figures and table
Equivalence of matter-type modified gravity theories to general relativity with nonminimal matter interaction
We show that gravity models, such as , and , that modify the introduction of
the material source in the usual Einstein-Hilbert action by adding only
matter-related terms to the matter Lagrangian density are
equivalent to general relativity with nonminimal interactions. Through the
redefinition ,
these models are exactly GR, yet the usual material field and its
accompanying partner, viz., the modification field
interact nonminimally. That is,
, where
is the interaction kernel that governs the rate of energy transfer.
We focus on the particular model, the energy-momentum squared gravity, where
the usual material field brings in an accompanying energy-momentum
squared field , along with a sui generis nonminimal
interaction between them. Compared to usual phenomenological nonminimal
interaction models in the literature, EMSF gives rise to more intricate
interaction kernels having covariant formulation even with simple forms of the
function. We elaborate upon EMSF via some different aspects: a DE component
induced from the interaction of sources such as cold dark matter and
relativistic species with their accompanying EMSFs generating interacting DE-DM
models, mimicking noncanonical scalar field, etc., or a Hoyle-type creation
field generating steady-state universe models extended to fluids other than
dust and a mimicker of modified generalized Chaplygin gas. We also demonstrate
the proper calculation of second metric variation of , as
well as in models that contain scalars like and .Comment: 16 pages, no figures and table
Screening in a new modified gravity model
We study a new model of Energy-Momentum Squared Gravity (EMSG), called
Energy-Momentum Log Gravity (EMLG), constructed by the addition of the term
, envisaged
as a correction, to the Einstein-Hilbert action with cosmological constant
. The choice of this modification is made as a specific way of
including new terms in the right-hand side of the Einstein field equations,
resulting in constant effective inertial mass density and, importantly, leading
to an explicit exact solution of the matter energy density in terms of
redshift. We look for viable cosmologies, in particular, an extension of the
standard CDM model. EMLG provides an effective dynamical dark energy
passing below zero at large redshifts, accommodating a mechanism for screening
in this region, in line with suggestions for alleviating some of the
tensions that arise between observational data sets within the standard
CDM model. We present a detailed theoretical investigation of the
model and then constrain the free parameter , a normalisation of
, using the latest observational data. The data does not rule out the
CDM limit of our model (), but prefers slightly negative
values of the EMLG model parameter (), which leads to
the screening of . We also discuss how EMLG relaxes the persistent
tension that appears in the measurements of within the standard
CDM model.Comment: 17 pages, 11 figures, 1 table; matches the version published in EPJ
A four-dimensional {\Lambda}CDM-type cosmological model induced from higher dimensions using a kinematical constraint
A class of cosmological solutions of higher dimensional Einstein field
equations with the energy-momentum tensor of a homogeneous, isotropic fluid as
the source are considered with an anisotropic metric that includes the direct
sum of a 3-dimensional (physical, flat) external space metric and an
n-dimensional (compact, flat) internal space metric. A simple kinematical
constraint is postulated that correlates the expansion rates of the external
and internal spaces in terms of a real parameter {\lambda}. A specific solution
for which both the external and internal spaces expand at different rates is
given analytically for n=3. Assuming that the internal dimensions were at
Planck length scales when the external space starts with a Big Bang (t=0), they
expand only 1.49 times and stay at Planck length scales even in the present age
of the universe (13.7 Gyr). The effective four dimensional universe would
exhibit a behavior consistent with our current understanding of the observed
universe. It would start in a stiff fluid dominated phase and evolve through
radiation dominated and pressureless matter dominated phases, eventually going
into a de Sitter phase at late times.Comment: 12 pages, 8 figures; matches the version published in General
Relativity and Gravitatio
Covid-19 and the quality of life of people with dementia and their carers—The TFD-C19 study
Introduction COVID-19 has placed unprecedented pressure on dementia health and social care systems worldwide. This has resulted in reduced services and support for people with dementia and their family carers. There are gaps in the evidence on the impact of the pandemic on Quality of Life (QoL). We carried out a study on the impact of the pandemic on the QoL of a group of people with dementia and their family carers who were part of a larger existing cohort study. Methods We quantitatively measured QoL, on two occasions during the two national lockdowns in 2020 and compared these data with those obtained when they entered the study (before the pandemic). Measures used included: DEMQOL-Proxy, Clinical Dementia Rating Scale and C-DEMQOL. To understand how QoL changed over time, a repeated measures ANOVA was run for each dependent variable with the following variables entered as co-variates: duration in study, baseline dementia severity, gender of the family carer, gender of the person with dementia, family carer relationship, dementia type, living status, age of the person with dementia, and age of the family carer. Results 248 participants took part in the study. QoL scores did not significantly decline between either time period for the person with dementia or their family carer. There was variation in subgroups; with co-resident status, carer relationship, gender of the person with dementia, age of the person with dementia, and baseline cognitive status influencing QoL outcomes in family carers. Discussion It is striking that people with dementia and their carers did not report a decline in QoL during the pandemic or in the months following restrictions suggesting the possibility of resilience. Variation in subgroups suggests that specific groups of family carers were more vulnerable to lower QoL; indicating the need for more tailored, nuanced support during this period. </jats:sec
Determining Eye–Hand Coordination Using the Sport Vision Trainer: An Evaluation of Test–Retest Reliability
Cosmology of a Scalar Field Coupled to Matter and an Isotropy-Violating Maxwell Field
Motivated by the couplings of the dilaton in four-dimensional effective
actions, we investigate the cosmological consequences of a scalar field coupled
both to matter and a Maxwell-type vector field. The vector field has a
background isotropy-violating component. New anisotropic scaling solutions
which can be responsible for the matter and dark energy dominated epochs are
identified and explored. For a large parameter region the universe expands
almost isotropically. Using that the CMB quadrupole is extremely sensitive to
shear, we constrain the ratio of the matter coupling to the vector coupling to
be less than 10^(-5). Moreover, we identify a large parameter region,
corresponding to a strong vector coupling regime, yielding exciting and viable
cosmologies close to the LCDM limit.Comment: Refs. added, some clarifications. Published in JHEP10(2012)06
Comparative study of actinic keratosis treatment with 3% diclofenac sodium and 5% 5-fluorouracil
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