ترغب بنشر مسار تعليمي؟ اضغط هنا

On the Chemical Potential of Dark Energy

11   0   0.0 ( 0 )
 نشر من قبل Saulo Pereira H
 تاريخ النشر 2008
  مجال البحث فيزياء
والبحث باللغة English
 تأليف S. H. Pereira




اسأل ChatGPT حول البحث

It is widely assumed that the observed universe is accelerating due to the existence of a new fluid component called dark energy. In this article, the thermodynamics consequences of a nonzero chemical potential on the dark energy component is discussed with special emphasis to the phantom fluid case. It is found that if the dark energy fluid is endowed with a negative chemical potential, the phantom field hypothesis becomes thermodynamically consistent with no need of negative temperatures as recently assumed in the literature.

قيم البحث

اقرأ أيضاً

The influence of a possible non zero chemical potential $mu$ on the nature of dark energy is investigated by assuming that the dark energy is a relativistic perfect simple fluid obeying the equation of state (EoS), $p=omega rho$ ($omega <0, constant$ ). The entropy condition, $S geq 0$, implies that the possible values of $omega$ are heavily dependent on the magnitude, as well as on the sign of the chemical potential. For $mu >0$, the $omega$-parameter must be greater than -1 (vacuum is forbidden) while for $mu < 0$ not only the vacuum but even a phantomlike behavior ($omega <-1$) is allowed. In any case, the ratio between the chemical potential and temperature remains constant, that is, $mu/T=mu_0/T_0$. Assuming that the dark energy constituents have either a bosonic or fermionic nature, the general form of the spectrum is also proposed. For bosons $mu$ is always negative and the extended Wiens law allows only a dark component with $omega < -1/2$ which includes vacuum and the phantomlike cases. The same happens in the fermionic branch for $mu <0$. However, fermionic particles with $mu >0$ are permmited only if $-1 < omega < -1/2$. The thermodynamics and statistical arguments constrain the EoS parameter to be $omega < -1/2$, a result surprisingly close to the maximal value required to accelerate a FRW type universe dominated by matter and dark energy ($omega lesssim -10/21$).
We argue that dark energy with multiple fields is theoretically well-motivated and predicts distinct observational signatures, in particular when cosmic acceleration takes place along a trajectory that is highly non-geodesic in field space. Such mode ls provide novel physics compared to $Lambda$CDM and quintessence by allowing cosmic acceleration on steep potentials. From the theoretical point of view, these theories can easily satisfy the conjectured swampland constraints and may in certain cases be technically natural, potential problems which are endemic to standard single-field dark energy. Observationally, we argue that while such multi-field models are likely to be largely indistinguishable from the concordance cosmology at the background level, dark energy perturbations can cluster, leading to an enhanced growth of large-scale structure that may be testable as early as the next generation of cosmological surveys.
We study a recently proposed formulation of overlap fermions at finite density. In particular we compute the energy density as a function of the chemical potential and the temperature. It is shown that overlap fermions with chemical potential reproduce the correct continuum behavior.
We present results for the phase diagram of QCD with two massless quark flavours as obtained from a first-principles functional renormalisation group approach. In particular we compute order parameters for chiral symmetry breaking and quark confineme nt at vanishing and non-zero imaginary chemical potential. Our analytical and numerical results suggest a close relation between the chiral and the deconfinement phase transition. We discuss the properties of dual order parameters at imaginary and real chemical potential.
In this study, we analyze how changes in the geometry of a potential energy surface in terms of depth and flatness can affect the reaction dynamics. We formulate depth and flatness in the context of one and two degree-of-freedom (DOF) Hamiltonian nor mal form for the saddle-node bifurcation and quantify their influence on chemical reaction dynamics. In a recent work, Garcia-Garrido, Naik, and Wiggins illustrated how changing the well-depth of a potential energy surface (PES) can lead to a saddle-node bifurcation. They have shown how the geometry of cylindrical manifolds associated with the rank-1 saddle changes en route to the saddle-node bifurcation. Using the formulation presented here, we show how changes in the parameters of the potential energy control the depth and flatness and show their role in the quantitative measures of a chemical reaction. We quantify this role of the depth and flatness by calculating the ratio of the bottleneck-width and well-width, reaction probability (also known as transition fraction or population fraction), gap time (or first passage time) distribution, and directional flux through the dividing surface (DS) for small to high values of total energy. The results obtained for these quantitative measures are in agreement with the qualitative understanding of the reaction dynamics.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا