1,733 research outputs found
Is Brane Inflation Eternal?
In this paper, we show that eternal inflation of the random walk type is
generically absent in the brane inflationary scenario. Depending on how the
brane inflationary universe originated, eternal inflation of the false vacuum
type is still quite possible. Since the inflaton is the position of the
D3-brane relative to the anti-D3-brane inside the compactified bulk with finite
size, its value is bounded. In DBI inflation, the warped space also restricts
the amplitude of the scalar fluctuation. These upper bounds impose strong
constraints on the possibility of eternal inflation. We find that eternal
inflation due to the random walk of the inflaton field is absent in both the
KKLMMT slow roll scenario and the DBI scenario. A more careful analysis for the
slow-roll case is also presented using the Langevin equation, which gives very
similar results. We discuss possible ways to obtain eternal inflation of the
random walk type in brane inflation. In the multi-throat brane inflationary
scenario, the branes may be generated by quantum tunneling and roll out the
throat. Eternal inflation of the false vacuum type inevitably happens in this
scenario due to the tunneling process. Since these scenarios have different
cosmological predictions, more data from the cosmic microwave background
radiation will hopefully select the specific scenario our universe has gone
through.Comment: 32 pages; v2: references and comments adde
Novel colours and the content of experience
I propose a counterexample to naturalistic representational theories of phenomenal character. The counterexample is generated by experiences of novel colours reported by Crane and Piantanida. I consider various replies that a representationalist might make, including whether novel colours could be possible colours of objects and whether one can account for novel colours as one would account for binary colours or colour mixtures. I argue that none of these strategies is successful and therefore that one cannot fully explain the nature of the phenomenal character of perceptual experiences using a naturalistic conception of representation
Exploring a string-like landscape
We explore inflationary trajectories within randomly-generated
two-dimensional potentials, considered as a toy model of the string landscape.
Both the background and perturbation equations are solved numerically, the
latter using the two-field formalism of Peterson and Tegmark which fully
incorporates the effect of isocurvature perturbations. Sufficient inflation is
a rare event, occurring for only roughly one in potentials. For models
generating sufficient inflation, we find that the majority of runs satisfy
current constraints from WMAP. The scalar spectral index is less than 1 in all
runs. The tensor-to-scalar ratio is below the current limit, while typically
large enough to be detected by next-generation CMB experiments and perhaps also
by Planck. In many cases the inflationary consistency equation is broken by the
effect of isocurvature modes.Comment: 24 pages with 8 figures incorporated, matches version accepted by
JCA
Brane Inflation and the Overshoot Problem
We investigate recent claims that brane inflation solves the overshoot
problem through a combination of microphysical restrictions on the phase space
of initial conditions and the existence of the Dirac-Born-Infeld (DBI)
attractor in regimes where the slow-roll attractor does not apply. Carrying out
a comprehensive analysis of the parameter space allowed by the latest advances
in brane inflation model-building, we find that these restrictions are
insufficient to solve the overshoot problem. The vast majority of the phase
space of initial conditions is still dominated by overshoot trajectories. We
present an analytic proof that the brane-inflationary attractor must be close
to the slow-roll limit, and update the predictions for observables such as
non-Gaussianity, cosmic string tension and tensor modes.Comment: 14 pages, 3 figures, matches version published in PRD. Minor
clarifications, references adde
Accelerating universe emergent from the landscape
We propose that the existence of the string landscape suggests the universe
can be in a quantum glass state, where an extremely large viscosity is
generated, and long distance dynamics slows down. At the same time, the short
distance dynamics is not altered due to the separation of time scales. This
scenario can help to understand some controversies in cosmology, for example
the natural existence of slow roll inflation and dark energy in the landscape,
the apparent smallness of the cosmological constant. We see also that moduli
stabilization is no longer necessary. We further identify the glass transition
point, where the viscosity diverges, as the location of the cosmic horizon. We
try to reconstruct the geometry of the accelerating universe from the structure
of the landscape, and find that the metric should have an infinite jump when
crossing the horizon. We predict that the static coordinate metric for dS space
breaks down outside the horizon.Comment: 20 pages, no figures, harvma
Medical decision making using knowledge of patient identification as Aboriginal or Torres Strait Islander: what do medical students think?
Objective
Best-practices guidelines require Australian health practitioners to ask all patients âare you [is the person] of Aboriginal and/or Torres Strait Islander origin?â. The present study investigated medical student attitudes regarding medical decisions made after asking this standard status question.
Methods
A hypothetical interaction between a doctor and an Aboriginal patient was presented in a pen-and-paper questionnaire in which: (1) the doctor considered (or did not consider) the patientâs Indigenous status relevant to make a medical diagnosis, and (2) the doctor registered (or did not register) the patient for the Closing the Gap PBS co-payment. Participants were first- and second-year medical students at the Australian National University who evaluated the doctorâs decisions against 20 attributes characterising professionalism and prejudice.
Results
Students evaluated the doctor more favourably when the doctor registered the patient for the co-payment and when the doctor did not consider Indigenous status relevant to making a medical diagnosis.
Conclusions
Encouragingly, medical students recognise that withholding registration for the co-payment is unprofessional. At the same time, medical students clearly do not think medical diagnoses should be made using the knowledge a patient identifies as Aboriginal.
Implications
With the continual development of policy and guidelines (and the prospect of diagnostic guidelines) to improve Aboriginal and Torres Strait Islander health, students and practitioners must understand how to use this knowledge of a patientâs status to benefit health outcomes
Seeing motion and apparent motion
In apparent motion experiments, participants are presented with what is in fact a succession of two brief stationary stimuli at two different locations, but they report an impression of movement. Philosophers have recently debated whether apparent motion provides evidence in favour of a particular account of the nature of temporal experience. I argue that the existing discussion in this area is premised on a mistaken view of the phenomenology of apparent motion and, as a result, the space of possible philosophical positions has not yet been fully explored. In particular, I argue that the existence of apparent motion is compatible with an account of the nature of temporal experience that involves a version of direct realism. In doing so, I also argue against two other claims often made about apparent motion, viz. that apparent motion is the psychological phenomenon that underlies motion experience in the cinema, and that apparent motion is subjectively indistinguishable from real motion
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