Matter fields from a decaying background Lambda vacuum

We suggest an alternative framework for interpreting the current state of the visible universe. Our approach is based on a dynamical ``Cosmological Constant'' and the starting point is that a decaying vacuum produces matter. As we point out, such a dynamical Lambda is not incompatible with the general requirements of general relativity. By assuming inflation and big bang nucleosynthesis we can solve for the present fractional densities of matter Omega_{m,0} and vacuum Omega_{Lambda, 0} in terms of only one parameter which we call the vacuum domination crossing redshift, z_c. We put constraints on z_c to obtain a universe that is presently vacuum dominated and with characteristic densities consistent with observations. The model points to the possible existence of newly formed dark matter in the inter-cluster voids. We argue that some of this matter could be accreting onto clusters through the latter's long range gravitational potentials. If so, then cluster dark matter halos may not manifest clear cut-offs in their radial density profiles. Furthermore, if a substantial amount of this newly produced matter has already drained onto the clusters, then the CMB power spectrum may favor lower dark matter density values than is currently observed bound in the clusters. A final feature of our approach relates to the combined effect of the matter production by a decaying vacuum and the different rates at which matter and the vacuum will dilute with the scale factor. Such combination may create conditions for a universe in which the vacuum and matter densities dilute and evolve towards comparable amplitudes. In this sense the model offers a natural and conceptually simple explanation to the Coincidence Problem.Comment: 22 pages, 1 figure, accepted for publication in Int. J. Mod. Phys. Lett.

Constraints On Cosmic Dynamics

Observationally, the universe appears virtually critical. Yet, there is no simple explanation for this state. In this article we advance and explore the premise that the dynamics of the universe always seeks equilibrium conditions. Vacuum-induced cosmic accelerations lead to creation of matter-energy modes at the expense of vacuum energy. Because they gravitate, such modes constitute inertia against cosmic acceleration. On the other extreme, the would-be ultimate phase of local gravitational collapse is checked by a phase transition in the collapsing matter fields leading to a de Sitter-like fluid deep inside the black hole horizon, and at the expense of the collapsing matter fields. As a result, the universe succumbs to neither vacuum-induced run-away accelerations nor to gravitationally induced spacetime curvature singularities. Cosmic dynamics is self-regulating. We discuss the physical basis for these constraints and the implications, pointing out how the framework relates and helps resolve standing puzzles such as "why did cosmic inflation end?", "why is Lambda small now?" and "why does the universe appear persistently critical?". The approach does, on the one hand, suggest a future course for cosmic dynamics, while on the other hand it provides some insight into the physics inside black hole horizons. The interplay between the background vacuum and matter fields suggests an underlying symmetry that links spacetime acceleration with spacetime collapse and global (cosmic) dynamics with local (black hole) dynamics.Comment: 11 page

Can gravitational collapse sustain singularity-free trapped surfaces?

In singularity generating spacetimes both the out-going and in-going expansions of null geodesic congruences $\theta ^{+}$ and $\theta ^{-}$ should become increasingly negative without bound, inside the horizon. This behavior leads to geodetic incompleteness which in turn predicts the existence of a singularity. In this work we inquire on whether, in gravitational collapse, spacetime can sustain singularity-free trapped surfaces, in the sense that such a spacetime remains geodetically complete. As a test case, we consider a well known solution of the Einstien Field Equations which is Schwarzschild-like at large distances and consists of a fluid with a $p=-\rho$ equation of state near $r=0$. By following both the expansion parameters $\theta ^{+}$ and $\theta ^{-}$ across the horizon and into the black hole we find that both $\theta ^{+}$ and $\theta ^{+}\theta ^{-}$ have turning points inside the trapped region. Further, we find that deep inside the black hole there is a region $0\leq r<r_{0}$ (that includes the black hole center) which is not trapped. Thus the trapped region is bounded both from outside and inside. The spacetime is geodetically complete, a result which violates a condition for singularity formation. It is inferred that in general if gravitational collapse were to proceed with a $p=-\rho$ fluid formation, the resulting black hole may be singularity-free.Comment: 17 pages, 3 figures, accepted for publication in International Journal of Modern Physics

The Gravitational Instability of the Vacuum: Insight into the Cosmological Constant Problem

A mechanism for suppressing the cosmological constant is developed, based on an analogy with a superconducting phaseshift in which free fermions coupled perturbatively to a weak gravitational field are in an unstable false vacuum state. The coupling of the fermions to the gravitational field generates fermion condensates with zero momentum and a phase transition induces a nonperturbative transition to a true vacuum state by producing a positive energy gap $\Delta$ in the vacuum energy, identified with $\sqrt{\Lambda}$, where $\Lambda$ is the cosmological constant. In the strong coupling limit a large cosmological constant induces a period of inflation in the early universe, followed by a weak coupling limit in which $\sqrt{\Lambda}$ vanishes exponentially fast as the universe expands due to the dependence of the energy gap on the density of Fermi surface fermions, $D({\epsilon})$, predicting a small cosmological constant in the present universe.Comment: 13 Page

UKZN Westville students’ use of on-campus Wi-Fi and their perceptions of quality of service.

Masters Degree. University of KwaZulu-Natal, Durban.As Higher Learning Institutions set up Wi-Fi infrastructure in different locations on-campus, they need to provide high quality services to support students’ learning. However, there has been little effort to ascertain how students use Wi-Fi on-campus, and how they perceive the quality of Wi-Fi in specific campus locations. Most research provides general information which makes it hard for Wi-Fi implementers to pinpoint the exact locations where services may need to be improved. This study follows a mixed method approach to present quantitative results from a representative sample of 373 students on UKZN Westville campus to understand how they use of Wi-Fi and their perceptions of service quality in different locations on-campus. It also presents qualitative information from interviews with two ICS administrators to understand Wi-Fi deployment strategies adopted on-campus and what Wi-Fi related problems students report. The most-used Wi-Fi locations were the on-campus residences (29.2%), the library (24.1%), computer LANs (17.4%) and lecture venues (17.2%). The worst Wi-Fi quality was reported in the Cafeteria (36.3%), the library (20.6%), and the Quad (15.4%). The best Wi-Fi quality was found in the computer LANs (34.2%), lecture venues (21.8%) and on-campus residences (11.8%). The Wi-Fi usage patterns are described according to the students’ accommodation type, as these patterns are very different. Best and worst times for using Wi-Fi in various locations is also given. The study showed that while students used various Wi-Fi devices to access Wi-Fi services on campus, the majority of them did not know the Wi-Fi standards, memory and speeds supported by their devices. When students faced difficulties, they stopped using Wi-Fi (38.6%), changed location (25.4%) or changed position in the same location (14.9%). Very few (8.6%) reported it to ICS. 86.3% did not know how to log a call with ICS. On-campus residence students reported Wi-Fi difficulties the most to ICS and they experienced the least difficulties in their residences. This shows that the ICS training for these students has paid off. The study bases its conceptual framework on the Brady & Cronin Jr. (2001) service quality model, which includes factors of outcome quality, physical environment quality and interaction quality. Outcome quality was used to understand students’ perception of the stability, availability reliability and timeliness of Wi-Fi services. Physical environment quality was used to understand the ambient conditions, social factors and design of the locations in which Wi-Fi is used. Interaction quality was used to understand the students’ perceptions of the behaviour, attitude and expertise quality of their interactions with ICS administrators. Overall, students rated the perceived Wi-Fi quality at just over 4.5 on a 7 point Likert scale. While this is greater than neutral, it can be improved. In a regression analysis of the constructs as a whole, the constructs account for 59.5% (R2 = .595) of the variance of service quality, F (3, 369) = 180.527, p<.0005. Outcome quality (β=.667, p<.0005), and interaction quality (β=.402, p=<.0005) are both significant predictors of service quality. However, physical environment quality is not. When regression models were generated for individual locations, for the most part, the R2 value improved. This study can be used by ICS to improve the Wi-Fi quality of service on campus, especially in areas where students use it the most, like in the library. ICS can also improve awareness of call logging amongst students, and how their choice of devices could affect their perceived Wi-Fi quality. The model could be used iteratively in future to test and monitor the quality of Wi-Fi services on campus, as well as in other environments, e.g. hospitals, hotels and airports

Cosmology with Interacting Dark Energy

The early cosmic inflation, when taken along with the recent observations that the universe is currently dominated by a low density vacuum energy, leads to at least two potential problems which modern cosmology must address. First, there is the old cosmological constant problem, with a new twist: the coincidence problem. Secondly, cosmology still lacks a model to predict the observed current cosmic acceleration and to determine whether or not there is a future exit out of this state (as previously in the inflationary case). This constitutes (what is called here) a dynamical problem. In this article a framework is proposed to address these two problems, based on treating the cosmic background vacuum (dark) energy as both dynamical and interacting. The universe behaves as a vacuum-driven cosmic engine which, in search of equilibrium, always back-reacts to vacuum-induced accelerations by increasing its inertia (internal energy) through vacuum energy dissipation. The process couples cosmic vacuum (dark) energy to matter to produce future-directed increasingly comparable amplitudes in these fields by setting up oscillations in the decaying vacuum energy density and corresponding sympathetic ones in the matter fields. By putting bounds on the relative magnitudes of these coupled oscillations the model offers a natural and conceptually simple channel to discuss the coincidence problem, while also suggesting a way to deal with the dynamical problem. A result with useful observational implications is an equation of state w(t) which specifically predicts a variable, quasi-periodic, acceleration for the current universe. This result can be directly tested by future observational techniques such as SNAP

Evolution of evaporating Black Holes in a higher dimensional inflationary universe

Spherically symmetric Black Holes of the Vaidya type are examined in an asymptotically de Sitter, higher dimensional spacetime. The various horizons are identified and located. The structure and dynamics of such horizons are studied. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87523/2/161_1.pd