Illuminating the nutritional nature of sponge-microbe symbioses

Sponges are present in virtually all aquatic environments around the globe and fulfil an important number of functional roles within ecosystems, largely resulting from their impressive water filtering capacity. These sessile filter feeders utilize a range of organic and inorganic nutrients from the water column via the interactivity of the sponge host and their diverse and abundant microbial symbionts. However, our understanding of the role of both host and microbiome in nutrient processing, particularly of dissolved organic matter (DOM), is limited. To address this knowledge gap, stable isotope probing and high-resolution imaging techniques (e.g. nanoscale secondary ion mass spectrometry), were applied to lab and field-based experiments. We found that both sponge cells and symbionts were actively involved in organic matter processing, with sponge filtering cells (choanocytes) being the primary site of organic matter uptake. We then quantified the uptake of DOM by host versus symbiont cells, showing that sponge cells were responsible for > 99 % of DOM uptake in sponges hosting low abundances of symbiotic microbes. Finally, we quantified the contribution of autotrophy and heterotrophy to the diet of a sponge hosting symbiotic cyanobacteria. Photosynthetic carbon fixation by cyanobacteria contributed approximately 7 % to total daily carbon uptake, which may prove beneficial for sponges under periods of limited food supply. Together, these findings provide a deeper understanding of the ancient relationship between sponges and their microbial symbionts, illuminating how they effectively capture and recycle nutrients

Evidence for charm-bottom tetraquarks and the mass dependence of heavy-light tetraquark states from lattice QCD

We continue our study of heavy-light four-quark states and find evidence from lattice QCD for the existence of a strong-interaction-stable $I(J^P)=0(1^+)$ $ud\bar{c}\bar{b}$ tetraquark with mass in the range of 15 to 61 MeV below $\bar{D}B^*$ threshold. Since this range includes the electromagnetic $\bar{D}B\gamma$ decay threshold, current uncertainties do not allow us to determine whether such a state would decay electromagnetically, or only weakly. We also perform a study at fixed pion mass, with NRQCD for the heavy quarks, simulating $qq^\prime \bar{b}^\prime \bar{b}$ and $q q^\prime \bar{b}^\prime\bar{b}^\prime$ tetraquarks with $q,\, q^\prime =ud$ or $\ell s$ and variable, unphysical $m_{b^\prime}$ in order to investigate the heavy mass-dependence of such tetraquark states. We find that the dependence of the binding energy follows a phenomenologically-expected form and that, though NRQCD breaks down before $m_{b^\prime}=m_c$ is reached, the results at higher $m_{b^\prime}$ clearly identify the $ud\bar{b}^\prime \bar{b}$ channel as the most likely to support a strong-interaction-stable tetraquark state at $m_{b^\prime}=m_c$. This observation serves to motivate the direct $ud\bar{c}\bar{b}$ simulation. Throughout we use dynamical $n_f=2+1$ ensembles with pion masses $m_\pi=$415, 299, and 164 MeV reaching down almost to the physical point, a relativistic heavy quark prescription for the charm quark, and NRQCD for the bottom quark(s).Comment: 24 pages, 4 figure

Dark Matter from Strong Dynamics: The Minimal Theory of Dark Baryons

As a simple model for dark matter, we propose a QCD-like theory based on $\rm{SU}(2)$ gauge theory with one flavor of dark quark. The model is confining at low energy and we use lattice simulations to investigate the properties of the lowest-lying hadrons. Compared to QCD, the theory has several peculiar differences: there are no Goldstone bosons or chiral symmetry restoration when the dark quark becomes massless; the usual global baryon number symmetry is enlarged to $\rm{SU}(2)_B$, resembling isospin; and baryons and mesons are unified together in $\rm{SU}(2)_B$ iso-multiplets. We argue that the lightest baryon, a vector boson, is a stable dark matter candidate and is a composite realization of the hidden vector dark matter scenario. The model naturally includes a lighter state, the analog of the $\eta^\prime$ in QCD, for dark matter to annihilate into to set the relic density via thermal freeze-out. Dark matter baryons may also be asymmetric, strongly self-interacting, or have their relic density set via $3 \to 2$ cannibalizing transitions. We discuss some experimental implications of coupling dark baryons to the Higgs portal.Comment: 26 pages, 16 figure

Neutral kaon mixing beyond the standard model with nf=2+1 chiral fermions

We compute the hadronic matrix elements of the four-quark operators needed for the study of neutral kaon mixing beyond the Standard Model (SM). We use nf=2+1 flavours of domain-wall fermions (DWF) which exhibit good chiral-flavour symmetry. The renormalization is performed non-perturbatively through the RI-MOM scheme and our results are converted perturbatively to MSbar. The computation is performed on a single lattice spacing a=0.086 fm with a lightest unitary pion mass of 290 MeV. The various systematic errors, including the discretisation effects, are estimated and discussed. Our results confirm a previous quenched study, where large ratios of non-SM to SM matrix elements were obtained.Comment: 5 pages, 4 figures, 1 table. v2 paper version, R3 and B3 corrected, conversion to 2GeV added, references adde