Accretion of Dissipative Dark Matter onto Active Galactic Nuclei

We examine the possibility that accretion of Dissipative Dark Matter (DDM) onto Active Galactic Nuclei (AGN) contributes to the growth rate of Super Massive Black Holes (SMBHs). Such a scenario could alleviate tension associated with anomalously large SMBHs measured at very early cosmic times, as well as observations that indicate that the growth of the most massive SMBHs occurs before $z\sim6$, with little growth at later times. These observations are not readily explained within standard AGN theory. We find a range in the parameter space of DDM models where we both expect efficient accretion to occur and which is consistent with observations of a large sample of measured SMBHs. When DDM accretion is included, the predicted evolution of this sample seems to be more consistent with assumptions regarding maximal BH seed masses and maximal AGN luminosities.Comment: Typos and affiliations correcte

The Irreducible Axion Background

Searches for dark matter decaying into photons constrain its lifetime to be many orders of magnitude larger than the age of the Universe. A corollary statement is that the abundance of any particle that can decay into photons over cosmological timescales is constrained to be much smaller than the cold dark-matter density. We show that an $\textit{irreducible}$ freeze-in contribution to the relic density of axions is in violation of that statement in a large portion of the parameter space. This allows us to set stringent constraints on axions in the mass range $100\rm \;eV - 100\; MeV$. At $10\rm \; keV$ our constraint on a photophilic axion is $g_{a\gamma \gamma} \lesssim 8.1 \times 10^{-14}~{\rm GeV}^{-1}$, almost three orders of magnitude stronger than the bounds established using horizontal branch stars; at $100~{\rm keV}$ our constraint on a photophobic axion coupled to electrons is $g_{aee} \lesssim 8.0 \times 10^{-15}$, almost four orders of magnitude stronger than present results. Although we focus on axions, our argument is more general and can be extended to, for instance, sterile neutrinos.Comment: 7+14 pages, 2+9 figures; v2 additional references and updated to the latest INTEGRAL constraint

The Inconsistency of Superfluid Dark Matter with Milky Way Dynamics

There are many well-known correlations between dark matter and baryons that exist on galactic scales. These correlations can essentially be encompassed by a simple scaling relation between observed and baryonic accelerations, historically known as the Mass Discrepancy Acceleration Relation (MDAR). The existence of such a relation has prompted many theories that attempt to explain the correlations by invoking additional fundamental forces on baryons. The standard lore has been that a theory that reduces to the MDAR on galaxy scales but behaves like cold dark matter (CDM) on larger scales provides an excellent fit to data, since CDM is desirable on scales of clusters and above. However, this statement should be revised in light of recent results showing that a fundamental force that reproduces the MDAR is challenged by Milky Way dynamics. In this study, we test this claim on the example of Superfluid Dark Matter. We find that a standard CDM model is strongly preferred over a static superfluid profile. This is due to the fact that the superfluid model over-predicts vertical accelerations, even while reproducing galactic rotation curves. Our results establish an important criterion that any dark matter model must satisfy within the Milky Way.Comment: 6+5 pages, 2+4 figure

An Innovative Influenza Vaccination Policy: Targeting Last Season's Patients

Influenza vaccination is the primary approach to prevent influenza annually. WHO/CDC recommendations prioritize vaccinations mainly on the basis of age and co-morbidities, but have never considered influenza infection history of individuals for vaccination targeting. We evaluated such influenza vaccination policies through small-world contact networks simulations. Further, to verify our findings we analyzed, independently, large-scale empirical data of influenza diagnosis from the two largest Health Maintenance Organizations in Israel, together covering more than 74% of the Israeli population. These longitudinal individual-level data include about nine million cases of influenza diagnosed over a decade. Through contact network epidemiology simulations, we found that individuals previously infected with influenza have a disproportionate probability of being highly connected within networks and transmitting to others. Therefore, we showed that prioritizing those previously infected for vaccination would be more effective than a random vaccination policy in reducing infection. The effectiveness of such a policy is robust over a range of epidemiological assumptions, including cross-reactivity between influenza strains conferring partial protection as high as 55%. Empirically, our analysis of the medical records confirms that in every age group, case definition for influenza, clinical diagnosis, and year tested, patients infected in the year prior had a substantially higher risk of becoming infected in the subsequent year. Accordingly, considering individual infection history in targeting and promoting influenza vaccination is predicted to be a highly effective supplement to the current policy. Our approach can also be generalized for other infectious disease, computer viruses, or ecological networks

Decadal Trends in Abundance, Size and Condition of Antarctic Toothfish in McMurdo Sound, Antarctica, 1972-2010

We report analyses of a dataset spanning 38 years of near-annual fishing for Antarctic toothfish Dissostichus mawsoni, using a vertical setline through the fast ice of McMurdo Sound, Antarctica, 1972-2010. This constitutes one of the longest biological time series in the Southern Ocean, and certainly the longest for any fish. Fish total length, condition and catch per unit effort (CPUE) were derived from the more than 5500 fish caught. Contrary to expectation, length-frequency was dominated by fish in the upper half of the industrial catch. The discrepancy may be due to biases in the sampling capabilities of vertical (this study) versus benthic (horizontal) fishing gear (industry long lines), related to the fact that only large Antarctic toothfish (more than 100 cm TL) are neutrally buoyant and occur in the water column. Fish length and condition increased from the early 1970s to the early 1990s and then decreased, related to sea ice cover, with lags of 8 months to 5 years, and may ultimately be related to the fishery (which targets large fish) and changes in the Southern Annular Mode through effects on toothfish main prey, Antarctic silverfish Pleuragramma antarcticum. CPUE was constant through 2001 and then decreased dramatically, likely related to the industrial fishery, which began in 1996 and which concentrates effort over the Ross Sea slope, where tagged McMurdo fish have been found. Due to limited prey choices and, therefore, close coupling among mesopredators of the Ross Sea, Antarctic toothfish included, the fishery may be altering the trophic structure of the Ross Sea

Day-Level Associations Between Substance Use and HIV Risk Behavior Among a Diverse Sample of Transgender Women

Purpose: Transgender women in the United States face elevated rates of HIV and of substance use. Studies measuring overall or aggregate levels of substance use have linked use to increased HIV transmission risk behavior (TRB). Although intensive longitudinal studies in other populations have found day-level links between substance use and TRB, no study has yet explored such links among transgender women. This study aimed to fill this gap in the literature. Methods: Utilizing survey and 60-day timeline follow-back interview data from a sample of 214 transgender women in New York City, we tested whether day-level heavy drinking, marijuana use, and/or nonprescription stimulant use were associated with odds of engaging in any sex (vs. no sexual activity) or engaging in TRB (vs. sex without TRB), adjusting for overall levels of use. Results: Multilevel models showed that each of the three substance types was associated with greater odds of engaging in sex on a given day—and more strongly so for heavy drinking among those with higher rates of heavy drinking, and for stimulant use among those with lower rates of stimulant use. Only marijuana use was associated with greater odds of TRB on a given day, but only among those with higher rates of use. Conclusion: These findings substantiate day-level links between substance use and engaging in sexual activity among transgender women, and importantly, between marijuana use and greater likelihood of TRB on a day when sexual activity occurs. This highlights the importance of addressing substance use for sexual health among transgender women especially focusing on marijuana use

Abstracts of the 2014 Brains, Minds, and Machines Summer School

A compilation of abstracts from the student projects of the 2014 Brains, Minds, and Machines Summer School, held at Woods Hole Marine Biological Lab, May 29 - June 12, 2014.This work was supported by the Center for Brains, Minds and Machines (CBMM), funded by NSF STC award CCF-1231216

A Formal Proof of PAC Learnability for Decision Stumps

We present a formal proof in Lean of probably approximately correct (PAC) learnability of the concept class of decision stumps. This classic result in machine learning theory derives a bound on error probabilities for a simple type of classifier. Though such a proof appears simple on paper, analytic and measure-theoretic subtleties arise when carrying it out fully formally. Our proof is structured so as to separate reasoning about deterministic properties of a learning function from proofs of measurability and analysis of probabilities.Comment: 13 pages, appeared in Certified Programs and Proofs (CPP) 202