Homogeneous Instantons in Bigravity

We study homogeneous gravitational instantons, conventionally called the Hawking-Moss (HM) instantons, in bigravity theory. The HM instantons describe the amplitude of quantum tunneling from a false vacuum to the true vacuum. Corrections to General Relativity (GR) are found in a closed form. Using the result, we discuss the following two issues: reduction to the de Rham-Gabadadze-Tolley (dRGT) massive gravity and the possibility of preference for a large $e$-folding number in the context of the Hartle-Hawking (HH) no-boundary proposal. In particular, concerning the dRGT limit, it is found that the tunneling through the so-called self-accelerating branch is exponentially suppressed relative to the normal branch, and the probability becomes zero in the dRGT limit. As far as HM instantons are concerned, this could imply that the reduction from bigravity to the dRGT massive gravity is ill-defined.Comment: 20 pages, 2 figures, comments and references adde

Sparse Message Passing Based Preamble Estimation for Crowded M2M Communications

Due to the massive number of devices in the M2M communication era, new challenges have been brought to the existing random-access (RA) mechanism, such as severe preamble collisions and resource block (RB) wastes. To address these problems, a novel sparse message passing (SMP) algorithm is proposed, based on a factor graph on which Bernoulli messages are updated. The SMP enables an accurate estimation on the activity of the devices and the identity of the preamble chosen by each active device. Aided by the estimation, the RB efficiency for the uplink data transmission can be improved, especially among the collided devices. In addition, an analytical tool is derived to analyze the iterative evolution and convergence of the SMP algorithm. Finally, numerical simulations are provided to verify the validity of our analytical results and the significant improvement of the proposed SMP on estimation error rate even when preamble collision occurs.Comment: submitted to ICC 2018 with 6 pages and 4 figure

Do Emotion Words Influence Age Effects in Delayed Match-to-Sample Performance for Emotional Faces?

Age differences are apparent in using verbal labels of emotion to categorize emotion face stimuli. Particularly, older adults have more difficulty detecting emotion cues like anger and fear relative to younger adults, but seem to have less difficulty with disgust cues. However, age differences are diminished in situations when participants are limited to two possible emotion choices or are required to simply match stimuli based on emotion cues without the use of labels. One question that emerges from the disparities in these findings is the role that emotion labels themselves play in driving possible age differences in emotion perception. The current study asked younger and older adults to perform a match-to-sample task in which, after being primed with an emotion label, they observed a mixed emotion stimulus (e.g., combination of anger and disgust) and then indicated which of two face standards was identical to the original stimulus. The standards were manipulated such that, paired with the original stimulus, participants also observed a second standard that was dominated by one of the emotions found in the initial mixed emotion stimulus. Should participants be primed by the dominating emotion, they would be more likely to misremember the initial stimulus by choosing the standard stimulus with a stronger emotional signal for the emotion specified in the word prime. The results showed similar performance among the control condition and the conditions of different dominating emotion in both age groups, indicating that younger and older adults relied on facial cues from the initial stimulus rather than the conceptual information found in the word primes to match the standard stimulus to the target. While age differences were limited, a correlation analysis demonstrated that fluid cognitive abilities may matter more to older adults’ performance than to younger adults’ performance in the memory task. Additional questions were also discussed for future studies to address and fully understand how exactly lexical stimuli might influence face perception and memory performance in a delayed match-to-sample task