Wormhole solutions in f(R,Lm)f(R,L_m) gravity

In this work, we intend to explore wormhole geometries in the framework of $f(R,L_m)$ gravity. We derive the field equations for the generic $f(R,L_m)$ function by assuming the static and spherically symmetric Morris-Thorne wormhole metric. Then we consider two non-linear $f(R,L_m)$ model, specifically, $f(R,L_m)=\frac{R}{2}+L_m^\alpha$ and $f(R,L_m)=\frac{R}{2}+(1+\lambda R)L_m$, where $\alpha$ and $\lambda$ are free model parameters. We obtain the wormhole solutions by assuming three cases, namely, a linear barotropic EoS, anisotropic EoS, and isotropic EoS corresponding to model I. We observe that for both barotropic and anisotropic cases, the corresponding wormhole solutions obey the flaring-out condition under asymptotic background, while for the isotropic case, the shape function does not follow the flatness condition. Also, we find that the null energy condition exhibits negative behavior in the vicinity of the throat. Further, we consider two different shape functions to investigate the behavior of model II. We find some constraints on the model parameter for which the violation of the null energy condition exhibits. Finally, we employ the volume integral quantifier to calculate the amount of exotic matter required near the wormhole throat for both models. We conclude that the modification of standard GR can efficiently minimize the use of exotic matter and provide stable traversable wormhole solutions.Comment: Chinese Journal of Physics published versio

Dynamical system analysis of scalar field cosmology in coincident f(Q)f(Q) gravity

In this article, we investigate scalar field cosmology in the coincident $f(Q)$ gravity formalism. We calculate the motion equations of $f(Q)$ gravity under the flat Friedmann-Lema\^{i}tre-Robertson-Walker background in the presence of a scalar field. We consider a non-linear $f(Q)$ model, particularly $f(Q)=-Q+\alpha Q^n$, which is nothing but a polynomial correction to the STEGR case. Further, we assumed two well-known specific forms of the potential function, specifically the exponential from $V(\phi)= V_0 e^{-\beta \phi}$ and the power-law form $V(\phi)= V_0\phi^{-k}$. We employ some phase-space variables and transform the cosmological field equations into an autonomous system. We calculate the critical points of the corresponding autonomous systems and examine their stability behaviors. We discuss the physical significance corresponding to the exponential case for parameter values $n=2$ and $n=-1$ with $\beta=1$, and $n=-1$ with $\beta=\sqrt{3}$. Moreover, we discuss the same corresponding to the power-law case for the parameter value $n=-2$ and $k=0.16$. We also analyze the behavior of corresponding cosmological parameters such as scalar field and dark energy density, deceleration, and the effective equation of state parameter. Corresponding to the exponential case, we find that the results obtained for the parameter constraints in Case III is better among all three cases, and that represents the evolution of the universe from a decelerated stiff era to an accelerated de-Sitter era via matter-dominated epoch. Further, in the power-law case, we find that all trajectories exhibit identical behavior, representing the evolution of the universe from a decelerated stiff era to an accelerated de-Sitter era. Lastly, we conclude that the exponential case shows better evolution as compared to the power-law case.Comment: Comments are welcom

Viscous fluid cosmology in symmetric teleparallel gravity

In this manuscript, we analyze the viscous fluid cosmological model in the framework of recently proposed $f(Q)$ gravity by assuming three different forms of bulk viscosity coefficients, specifically, $(i)\zeta =\zeta_{0}+\zeta_{1}\left( \frac{\dot{a}}{a}\right) +\zeta_{2}\left( \frac{{\ddot{a}}}{\dot{a}}\right)$, $(ii)\zeta =\zeta_{0}+\zeta_{1}\left( \frac{\dot{a}}{a}\right)$, and $(iii)\zeta =\zeta_{0}$ and a linear $f(Q)$ model, particularly, $f(Q)=\alpha Q$ where $\alpha \neq 0$ is free model parameter. We estimate the bulk viscosity coefficients and the model parameter values using the combined H(z)+Pantheon+BAO data set. We study the asymptotic behavior of our cosmological bulk viscous model by utilizing the phase space method. We find that corresponding to all three cases, our model depicts the evolution of the universe from matter dominated decelerated epoch (a past attractor) to a stable de-sitter accelerated epoch ( a future attractor). Further, we study the physical behavior of effective pressure, effective equation of state (EoS), and the statefinder parameters. We find that the pressure component in the presence of bulk viscosity shows negative behavior and the effective EoS parameter predicts the accelerated expansion phase of the universe for all three cases. Moreover, we obtain that the trajectories of our model lie in the quintessence region and it converges to the $\Lambda$CDM fixed point in the far future. Thus we can conclude that our viscous fluid cosmological model can efficiently describe late time accelerated expansion phase of the universe corresponding to all three cases.Comment: Comments are welcom

f(Q,T)f(Q,T) gravity, its covariant formulation, energy conservation and phase-space analysis

In the present article we analyze the matter-geometry coupled $f(Q,T)$ theory of gravity. We offer the fully covariant formulation of the theory, with which we construct the correct energy balance equation and employ it to conduct a dynamical system analysis in a spatially flat Friedmann-Lema\^{i}tre-Robertson-Walker spacetime. We consider three different functional forms of the $f(Q,T)$ function, specifically, $f(Q,T)=\alpha Q+ \beta T$, $f(Q,T)=\alpha Q+ \beta T^2$, and $f(Q,T)=Q+ \alpha Q^2+ \beta T$ . We attempt to investigate the physical capabilities of these models to describe various cosmological epochs. We calculate Friedmann-like equations in each case and introduce some phase space variables to simplify the equations in more concise forms. We observe that the linear model $f(Q,T)=\alpha Q+ \beta T$ with $\beta=0$ is completely equivalent to the GR case without cosmological constant $\Lambda$. Further, we find that the model $f(Q,T)=\alpha Q+ \beta T^2$ with $\beta \neq 0$ successfully depicts the observed transition from decelerated phase to an accelerated phase of the universe. Lastly, we find that the model $f(Q,T)= Q+ \alpha Q^2+ \beta T$ with $\alpha \neq 0$ represents an accelerated de-Sitter epoch for the constraints $\beta < -1$ or $\beta \geq 0$.Comment: EPJC accepted versio

Bulk viscous fluid in symmetric teleparallel cosmology: theory versus experiment

The standard formulation of General Relativity Theory, in the absence of a cosmological constant, is unable to explain the responsible mechanism for the observed late-time cosmic acceleration. On the other hand, by inserting the cosmological constant in Einstein's field equations it is possible to describe the cosmic acceleration, but the cosmological constant suffers from an unprecedented fine-tunning problem. This motivates one to modify Einstein's space-time geometry of General Relativity. The $f(Q)$ modified theory of gravity is an alternative theory to General Relativity, where the non-metricity scalar $Q$ is the responsible candidate for gravitational interactions. In the present work we consider a Friedmann-Lem\^aitre-Robertson-Walker cosmological model dominated by bulk viscous cosmic fluid in $f(Q)$ gravity with the functional form $f(Q)=\alpha Q^n$, where $\alpha$ and $n$ are free parameters of the model. We constrain our model with the recent Pantheon supernovae data set of 1048 data points, Hubble data set of 31 data points and baryon acoustic oscillations data set consisting of six points. For higher values of redshift, it is clear that the $f(Q)$ cosmology better fits data than standard cosmology. We present the evolution of our deceleration parameter with redshift and it properly predicts a transition from decelerated to accelerated phases of the universe expansion. Also, we present the evolution of density, bulk viscous pressure and the effective equation of state parameter with redshift. Those show that bulk viscosity in a cosmic fluid is a valid candidate to acquire the negative pressure to drive the cosmic expansion efficiently.We also examine the behavior of different energy conditions to test the viability of our cosmological $f(Q)$ model. Furthermore, the statefinder diagnostics are also investigated in order to distinguish among different dark energy models.Comment: Comments are welcom

Scalar field evolution at background and perturbation levels for a broad class of potentials

In this paper, we investigate a non-interacting scalar field cosmology with an arbitrary potential using the $f$-deviser method that relies on the differentiability properties of the potential. Using this alternative mathematical approach, we present a unified dynamical system analysis at a scalar field's background and perturbation levels with arbitrary potentials. For illustration, we consider a monomial and double exponential potentials. These two classes of potentials comprise the asymptotic behaviour of several classes of scalar field potentials, and, therefore, they provide the skeleton for the typical behaviour of arbitrary potentials. Moreover, we analyse the linear cosmological perturbations in the matterless case by considering three scalar perturbations: the evolution of the Bardeen potentials, the comoving curvature perturbation, the so-called Sasaki-Mukhanov variable, or the scalar field perturbation in uniform curvature gauge. Finally, an exhaustive dynamical system analysis for each scalar perturbation is presented.Comment: 65 pages, 8 compound figures. Major revision. References adde

ROTIFERS ABUNDANCE AND THEIR RELATIONSHIP TO WATER QUALITY IN THE PANDU LAKE, BODHAN, TELANGANA, INDIA

Abstract: In the present study an attempt has been made to evaluate water quality and related density of rotifers for a period of two years, August 2002 to July 2004. A few water quality parameters such as dissolved Oxygen, biological oxygen demand, phosphates, and nitrates are presented here to relate with the abundance or cessation of rotifers. The present study has given an understanding that lake is transforming into nutrient rich water body

Gastrointestinal Tuberculosis Presenting as Malnutrition and Distal Colonic Bowel Obstruction

Gastrointestinal (GI) tuberculosis (TB) is rare and can occur in the context of active pulmonary disease or as a primary infection with no pulmonary symptoms. It typically presents with vague abdominal symptoms, making it difficult to discern from alternative disease processes. Although the ileocecal region is the most commonly affected site, tuberculous enteritis can involve any aspect of the GI tract. To demonstrate the importance of maintaining a high clinical suspicion for the disease, we present a case of GI TB presenting as severe malnutrition and segmental colitis of the left colon

Gastrointestinal haemorrhage in extracorporeal membrane oxygenation: insights from the national inpatient sample

INTRODUCTION: Extracorporeal membrane oxygenation (ECMO) is associated with gastrointestinal haemorrhage (GIH), which may result from coagulopathy, systemic inflammation, reduced gastric perfusion, and arteriovenous malformation from non-pulsatile blood flow. Data are limited regarding the burden of this complication in the United States. MATERIAL AND METHODS: We analysed the National Inpatient Sample (NIS) database for the years 2007 to 2011 to identify hospitalisations in which an ECMO procedure was performed. Hospitalizations complicated by GIH in this cohort were then identified by relevant codes. RESULTS: Between 2007 and 2011, ECMO hospitalisations increased from 1869 to 3799 (p \u3c 0.01). The proportion of hospitalisations complicated by GIH increased from 2.12% in 2007 to 7.46% in 2011 (p \u3c 0.01). Gastrointestinal haemorrhage was more common in men (56.7%) and in Caucasians (57.4%). Common comorbidities in this population were renal failure (71%), anaemia (55%), and hypertension (26%). All-cause inpatient mortality showed a numerical but nonsignificant increase from 56.7% to 61.9% (p = 0.49). The average cost of care per hospitalisation with GIH associated with ECMO use increased from $132,420 in 2007 to$215,673 in 2011 (p \u3c 0.01). CONCLUSIONS: Gastrointestinal haemorrhage during ECMO hospitalisations occurred in small but significantly increasing proportions. The inpatient mortality rate and costs associated with GIH were substantial and increased significantly during the study period