Tests have to be performed to rule out proposals for gravity modification. We propose a new idea for constraining alternative theories of gravity using temperature-dependent white dwarf (WD) ...mass-radius (MR) observational data. We have shown that several alternatives to general relativity (GR), which modified GR only within matter, might be reduced to the well-known Poisson equation similar to that of Eddington-inspired Born Infeld (EiBI) and Minimal Exponential Measure (MEMe) gravity. Retaining EiBI notation, we constrain the value of the coupling constant,
κ
, using a high-precision model-independent measurement of WD MR observations. We have demonstrated that the WD model should include detailed physics to achieve good precision. The model should include their temperature and evolutionary aspects, which may be computationally expensive. To overcome this issue, we construct a semi-analytical surrogate model based on Mestel’s model, calibrated with tabulated, detailed realistic models, to correct the zero-temperature radius. We have shown that the best-fit value of
κ
depends on the WD model, with the ’thick’ envelope models more consistent in describing data. The tightest bound obtained from the most precise MR measurement, QS Vir, with
-
0.19
≲
κ
≲
0.22 in
10
3
m
5
kg
-
1
s
-
2
for
2
σ
(
∼
95
%
)
credibility. Overall, we assert that the recent precise WD MR measurements, combined with our current understanding of WD structure, are insufficient to see the deviation from the one predicted by GR. Both more precise observation data and detailed WD modelling are required to rule out gravity modification.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Due to their compactness, neutron stars are the best study matter in high density and strong-field gravity. Hartle and Thorne have proposed a good approximation or perturbation procedure within ...general relativity for slowly rotating relativistic stars by assuming the matter inside the stars is an ideal isotropic fluid. This study extends the analytical Hartle–Thorne formalism for slowly rotating neutron stars, including the possibility that the neutron star pressure can be anisotropic. We study the impact of neutron stars’ anisotropy pressure on mass correction and deformation numerically. For the anisotropic model, we use the Bowers-Liang model. For the equation of state of neutron stars, we use a relativistic mean-field BSP parameter set with the hyperons, and for the crust equation of state, we use the one of Miyatsu et al. We have found that the mass of neutron stars increases but the radius decreases by increasing
λ
BL
value. Therefore, the NS compactness increases when
λ
BL
becomes larger. This fact leads to a condition in which NS is getting harder to deformed when the
λ
BL
increased.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We use ideal fluid energy conditions to constrain the free parameter of the degree of nonconservation ζ of the energy-momentum tensor in Rastall gravity theory. We study the mass-radius relation of ...strange stars and the corresponding stability using the obtained range of ζ constrained by energy conditions. In our calculations, we use the MIT bag model with a color-flavor-locked state to describe strange quark matter. We obtain a finite, narrow range of 0 ≤ ζ ≤ 0.5 . In addition to ζ , the corresponding nonconservation of the energy-momentum tensor depends on the gradient of the energy-momentum scalar. The behavior of matter in the MIT bag model is one example in which the energy-momentum tensor is conserved through the zero value on the gradient of the energy-momentum scalar. We also find that the corresponding mass-radius relation of strange stars depends on the interplay of matter parameters, such as ms, B, Δ, and the Rastall parameter ζ . In addition, we find that as ζ increases, the maximum strange star mass decreases. Furthermore, the stability of strange stars with regard to radial oscillations in Rastall gravity theory is rather different from that in general relativity because of the impact of the nonconservation of the energy-momentum tensor. The stability boundary mass and radius determined from the zero modes of radial perturbation oscillations are not the same as the maximum mass and corresponding radius. This is because the Rastall nonconservation term increases the matter pressure to support the strange star against collapse, especially when v2s > 1/3. The reverse applies when v2s < 1/3.
It is reported (Estevez-Delgado and Estevez-Delgado in Eur Phys J C 78:673, 2018) recently, that the absence of anisotropic in compact object pressure leads to a solution which is not physically ...acceptable due to the energy density and speed of sound can not be positive at the origin at the same time. Here, we calculate the pressure and energy density of NSs using realistic EOS predicted by a relativistic mean-field model including hyperons for isotropic and three different anisotropic pressure models such as the one of Doneva and Yazadjiev (Phys Rev D 85:124023, 2012), the one of Herrera and Barreto (Phys Rev D 88:084022, 2013), and the one of Bowers and Liang (Astrophys J 188:657, 1974). We obtain that the all of energy conditions of perfect fluid are satisfied not only by anisotropic NSs profiles but also the one of isotropic NSs.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Motivated by a recent report by Biwas and Bose (Phys Rev D 99:104002, 2019) that the observations of GW170817 to constrain the extent of pressure anisotropy in neutron stars within Bower–Liang ...anisotropic model, we systematically study the effects of anisotropic pressure on properties of the neutron stars with hyperons. The equation of state is calculated using the relativistic mean-field model with a BSP parameter set to determine nucleonic coupling constants and by using SU(6) and hyperon potential depths to determine hyperonic coupling constants. We investigate three models of anisotropic pressure known in literature namely Bowers and Liang (Astrophys J 88:657, 1974), Horvat et al. (Class Quant Grav 28:025009, 2011), and Cosenza et al. (J Math Phys (NY) 22:118, 1981). The reliability of the equation of state used is checked by comparing the parameters of the corresponding EOS to recent experimental data. The mass–radius, moment of inertia, and tidal deformability results of Bowers–Liang, Horvat et al., and Cosenza et al. anisotropic models are compared to the corresponding recent results extracted from the analysis of some NS observation data. We have found that the radii predicted by anisotropic NS are sensitive to the anisotropic model used and the results obtained by using the model proposed by Horvat et al. with anisotropic free parameter
Υ
≈
-
1.15 are relative compatible with all taken constraints.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We implement a recent model proposed by Serrano–Liska (SL) (Alonso-Serrano and Liška, JHEP, 12:196, 2020) to study the ultra-compact star properties. The matter in the interior star is modeled by the ...quark model, deducted from QCD theory equipped with anisotropic pressure. Anisotropy is used to increase the compactness of the stars. We intend to see the signature of the “quantum gravity” effect through the SL model in ultra-compact stars. The SL model was motivated by quantum correction appearing in the black hole by adding a logarithmic term in gravity entropy used to derive the effective Einstein field equation. We expect this correction term in the SL model also affects ultra-compact star properties. The SL model with coupling constant
c
~
in logarithmic term equipped with spherically symmetric metric yields correction terms
O
(
c
~
)
that can be expressed by a function
Ξ
(
r
)
. The
Ξ
(
r
)
function vanishes at the star’s exterior. We found that the mass-radius relation prediction by the SL model with anisotropic matter deviates from the one predicted by the standard Tolman–Oppenheimer–Volkoff (TOV) equation for
c
~
≥
10
7
m
2
. We also have a sufficiently deep enough effective potential to produce a quasi-normal mode. We obtain the echo frequency of 15.2 kHz using maximum anisotropic pressure contribution and
c
~
=
10
7
m
2
. Because the corresponding effective potential is almost indistinguishable from that of GR, this echo frequency value can be indistinguishable to one of GR, but not comparable to the result from GW170817 data analysis, i.e., 72 Hz. To circumvent this problem, we can decrease the value of echo frequency by increasing the magnitude of
c
~
to orders of magnitude than
c
~
=
10
7
m
2
. On the other hand, too large a strength from the logarithmic correction term is not physically favored because we learn from the black hole case that the logarithmic term is expected to be smaller than that of the Bekenstein term. Therefore, more precise gravitation echo measurements are crucial to understand this issue.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We studied herein the mass and the radius of brown dwarfs predicted by beyond Horndeski (BH) and Eddington-inspired Born-Infeld (EiBI) gravity theories by numerically solving the modified ...non-relativistic hydrostatic equations of both theories. We used a recent compilation of brown dwarf masses and radii obtained from Ref. Bayliss et al. (Astrophys J 153:1, 2016) to constrain the free parameter of both theories. We obtain the range of the corresponding parameters with 1
σ
and 5
σ
confidence by using chi-squared analysis. Furthermore, the minimum chi-squared values can be reached for the cases of
κ
=
0.17
×
10
2
m
5
kg
-
1
s
-
2
and
γ
=
-
0.1207
for EiBI and BH theories, respectively. The corresponding parameter values with the minimum chi-squared values are relatively small; therefore, they cannot significantly change the brown dwarf mass limits determined from the equivalence of nuclear and photosphere luminosities for the pp (hydrogen burning) and pp+pd (deuterium burning) reactions.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Minimal length, nuclear matter, and neutron stars Prasetyo, I.; Belfaqih, I. H.; Wahidin, A. B. ...
The European physical journal. C, Particles and fields,
10/2022, Letnik:
82, Številka:
10
Journal Article
Recenzirano
Odprti dostop
In this paper, we employ one variant of the Generalized Uncertainty Principle (GUP) model, i.e., the Kempf–Mangano–Mann (KMM) model, and discuss the impact of GUP on the EoS of nuclear and neutron ...star matter based on the relativistic mean field (RMF) model. We input the result in the Serrano–Liška (SL) gravity theory to discuss the corresponding Neutron Star (NS) properties. We have shown that the upper bound for the GUP parameter from nuclear matter properties is
β
≤
2
×
10
-
7
MeV
-
2
. If we used this
β
upper bound to calculate NS matter, and considering SL parameter
c
~
as an independent parameter, we have found that the upper bound for the SL parameter, which modifies the Einstein field equation, is
c
~
≤
10
7
m
2
. This beta upper bound is determined by considering the anisotropy magnitude smaller than the pressure magnitude. By employing
β
=
2
×
10
-
7
MeV
-
2
and
c
~
=
10
7
m
2
, we obtain the mass–radius relation that satisfies NICER data for both PSR J0740+6620 (whose mass is
∼
2.1
M
⊙
) and PSR J0030+0451 (
M
∼
1.4
M
⊙
). Our GUP parameter upper bound perfectly matches the constraint from
87
Rb cold-atom-recoil experiment. If we consider that the same strength from the additional logarithmic term in the entropy from both GUP and SL model are dependent, for
β
<
2
×
10
-
7
MeV
-
2
, it is clear that SL parameter lower bound is
c
~
>
-
16
×
10
-
34
m
2
. The magnitude of this bound is
10
-
40
smaller than the upper bound magnitude of SL parameter considering as independent parameter i.e.,
c
~
≤
10
7
m
2
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The advantage of mapping modified gravity theories with standard matter into general relativity (GR) with modified matter is that we can quickly implement the well-established analytical and ...numerical methods developed within GR to study modified gravity theories and compare the modified gravity theories with current observational data. In this paper, we explicitly show that overturning/cracking instability may occur in an isotropic Eddington-inspired Born-Infeld (EiBI) stellar structure. Analyses are done by reducing the Tolman-Oppenheimer-Volkoff-like equations of EiBI into the ones of GR with an additional anisotropiclike nonlinear term. We obtain the term by expanding the stellar structure equations with respect to γκε and γκP and by using numerical calculations. We find that, for a specific value of κ, the overturning/cracking may occur. In the nonrelativistic regime, cracking tends to occur when κ>0. In the relativistic regime, for neutron stars (NS) with equation of state (EOS) based on a relativistic mean field model (RMF), the overturning occurs at κ≳0, and the overturning point is located near the core of the star. We also show that the stellar structure equations within EiBI theory with isotropic matter can be recast into GR defined in a physical metric g with a modified (apparent) anisotropic matter. In this representation, the signature of a potentially overturning instability within the apparent anisotropic structure is present and related to the asymptotic behavior of the apparent speed of sound near the center of the star and an imaginary value of the apparent tangential speed of sound near the edge of the star.
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