# Faculty Publications: February, 2014

Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)

The following are Harvard Physics faculty members' publications, added to the ADS database last month. Please note that some publications which appeared in print last month may not be included in the database (and therefore may not appear on this list) until the following month.

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Jan 2014

 Title: On the Ground State Wave Function of Matrix Theory Authors: Lin, Ying-Hsuan; Yin, Xi Publication: eprint arXiv:1402.0055 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 21 pages Bibliographic Code: 2014arXiv1402.0055L

### Abstract

We propose an explicit construction of the leading terms in the asymptotic expansion of the ground state wave function of BFSS SU(N) matrix quantum mechanics. Our proposal is consistent with the expected factorization property in various limits of the Coulomb branch, and involves a different scaling behavior from previous suggestions. We comment on some possible physical implications.

 Title: Cohomology and Hodge Theory on Symplectic Manifolds: III Authors: Tsai, Chung-Jun; Tseng, Li-Sheng; Yau, Shing-Tung Publication: eprint arXiv:1402.0427 Publication Date: 02/2014 Origin: ARXIV Keywords: Mathematics - Symplectic Geometry, High Energy Physics - Theory, Mathematics - Differential Geometry, Mathematics - Geometric Topology Comment: 68 pages Bibliographic Code: 2014arXiv1402.0427T

### Abstract

We introduce filtered cohomologies of differential forms on symplectic manifolds. They generalize and include the cohomologies discussed in Paper I and II as a subset. The filtered cohomologies are finite-dimensional and can be associated with differential elliptic complexes. Algebraically, we show that the filtered cohomologies give a two-sided resolution of Lefschetz maps, and thereby, they are directly related with the kernels and cokernels of the Lefschetz maps. We also introduce a novel, non-associative product operation on differential forms for symplectic manifolds. This product generates an A-infinity algebra structure on forms that underlies the filtered cohomologies and gives them a ring structure. As an application, we demonstrate how the ring structure of the filtered cohomologies can distinguish different symplectic four-manifolds in the context of a circle times a fibered three-manifold.

 Title: Evidence for $s$-channel Single-Top-Quark Production in Events with one Charged Lepton and two Jets at CDF Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors Publication: eprint arXiv:1402.0484 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: submitted to Phys. Rev. Lett Bibliographic Code: 2014arXiv1402.0484C

### Abstract

We report evidence for $s$-channel single-top-quark production in proton-antiproton collisions at center-of-mass energy $\sqrt{s}= 1.96~\mathrm{TeV}$ using a data set that corresponds to an integrated luminosity of $9.4~\mathrm{fb}^{-1}$ collected by the Collider Detector at Fermilab. We select events consistent with the $s$-channel process including two jets and one leptonically decaying $W$ boson. The observed significance is $3.8$ standard deviations with respect to the background-only prediction. Assuming a top-quark mass of $172.5~\mathrm{GeV}/c^2$, we measure the $s$-channel cross section to be $1.41^{+0.44}_{-0.42}~\mathrm{pb}$.

 Title: Quantum quenches and competing orders: II. quantum non-linear sigma model Authors: Hung, Ling-Yan; Fu, Wenbo; Sachdev, Subir Publication: eprint arXiv:1402.0875 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory Comment: 15 pages, 9 figures Bibliographic Code: 2014arXiv1402.0875H

### Abstract

We study the non-equilibrium dynamics of a quantum generalization of a O(6) non-linear sigma model of competing orders in the underdoped cuprates (Hayward {\em et al.}, arXiv:1309.6639). We obtain results, in the large $N$ limit of a O($N$) model, on the time-dependence of correlation functions following a pulse disturbance. We find that the oscillatory responses share various qualitative features with recent optical experiments.

 Title: Feedback induced phase transitions in active porous media Authors: Ocko, Samuel A.; Mahadevan, L. Publication: eprint arXiv:1402.1547 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Statistical Mechanics, Nonlinear Sciences - Adaptation and Self-Organizing Systems, Nonlinear Sciences - Cellular Automata and Lattice Gases Comment: 14 pages, 8 figures Bibliographic Code: 2014arXiv1402.1547O

### Abstract

Flow through passive porous media is typically described in terms of a linear theory relating current fluxes and driving forces, in the presence of a prescribed heterogeneous permeability. However, many porous systems such as glacial drainage networks, erosional river bed networks, vascular networks, social insect swarms and animal architectures such as termite mounds are continuously remodeled by the flow and thence modify the flow, i.e. they are active. Here we consider a minimal model for an active porous medium where flow and resistance are coupled to each other. Using numerical simulations, we show that this results in both channelization and wall-building transitions depending on the form of the feedback. A continuum model allows us to understand the qualitative features of the resulting phase diagram, and suggests ways to realize complex architectures using simple rules in engineered systems.

 Title: Indirect measurement of $\sin^2 \theta_W$ (or $M_W$) using $\mu^+\mu^-$ pairs from $\gamma^*/Z$ bosons produced in $p\bar{p}$ collisions at a center-of-momentum energy of 1.96 TeV Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.; Anastassov, A.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors Publication: eprint arXiv:1402.2239 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Experiment Bibliographic Code: 2014arXiv1402.2239C

### Abstract

Drell-Yan lepton pairs are produced in the process $p\bar{p} \rightarrow \mu^+\mu^- + X$ through an intermediate $\gamma^*/Z$ boson. The forward-backward asymmetry in the polar-angle distribution of the $\mu^-$ as a function of the invariant mass of the $\mu^+\mu^-$ pair is used to obtain the effective leptonic determination $\sin^2 \theta^{lept}_{eff}$ of the electroweak-mixing parameter $\sin^2 \theta_W$, from which the value of $\sin^2 \theta_W$ is derived assuming the standard model. The measurement sample, recorded by the Collider Detector at Fermilab (CDF), corresponds to 9.2 fb-1 of integrated luminosity from $p\bar{p}$ collisions at a center-of-momentum energy of 1.96 TeV, and is the full CDF Run II data set. The value of $\sin^2 \theta^{lept}_{eff}$ is found to be 0.2315 +- 0.0010, where statistical and systematic uncertainties are combined in quadrature. When interpreted within the context of the standard model using the on-shell renormalization scheme, where $\sin^2 \theta_W = 1 - M_W^2/M_Z^2$, the measurement yields $\sin^2 \theta_W$ = 0.2233 +- 0.0009, or equivalently a W-boson mass of 80.365 +- 0.047 GeV/c^2. The value of the W-boson mass is in agreement with previous determinations in electron-positron collisions and at the Tevatron collider.

 Title: Many-body dynamics of dipolar molecules in an optical lattice Authors: Hazzard, Kaden R. A.; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A.; Covey, Jacob P.; Yao, Norman Y.; Lukin, Mikhail D.; Ye, Jun; Jin, Deborah S.; Rey, Ana Maria Publication: eprint arXiv:1402.2354 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases, Physics - Atomic Physics, Quantum Physics Bibliographic Code: 2014arXiv1402.2354H

### Abstract

Understanding the many-body dynamics of isolated quantum systems is one of the central challenges in modern physics. To this end, the direct experimental realization of strongly correlated quantum systems allows one to gain insights into the emergence of complex phenomena. Such insights enable the development of theoretical tools that broaden our understanding. Here, we theoretically model and experimentally probe with Ramsey spectroscopy the quantum dynamics of disordered, dipolar-interacting, ultracold molecules in a partially filled optical lattice. We report the capability to control the dipolar interaction strength, and we demonstrate that the many-body dynamics extends well beyond a nearest-neighbor or mean-field picture, and cannot be quantitatively described using previously available theoretical tools. We develop a novel cluster expansion technique and demonstrate that our theoretical method accurately captures the measured dependence of the spin dynamics on molecule number and on the dipolar interaction strength. In the spirit of quantum simulation, this agreement simultaneously benchmarks the new theoretical method and verifies our microscopic understanding of the experiment. Our findings pave the way for numerous applications in quantum information science, metrology, and condensed matter physics.

 Title: Measuring Z2 topological invariants in optical lattices using interferometry Authors: Grusdt, Fabian; Abanin, Dmitry; Demler, Eugene Publication: eprint arXiv:1402.2434 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases Comment: 17 pages, 13 figures, 6 pages appendix Bibliographic Code: 2014arXiv1402.2434G

### Abstract

We propose an interferometric method to measure Z2 topological invariants of time-reversal invariant topological insulators realized with optical lattices in two and three dimensions. We suggest two schemes which both rely on a combination of Bloch oscillations with Ramsey interferometry and can be implemented using standard tools of atomic physics. In contrast to topological Zak phase and Chern number, defined for individual 1D and 2D Bloch bands, the formulation of the Z2 invariant involves at least two Bloch bands related by time- reversal symmetry which one has keep track of in measurements. In one of our schemes this can be achieved by the measurement of Wilson loops, which are non-Abelian generalizations of Zak phases. The winding of their eigenvalues is related to the Z2 invariant. We thereby demonstrate that Wilson loops are not just theoretical concepts but can be measured experimentally. For the second scheme we introduce a generalization of time-reversal polarization which is continuous throughout the Brillouin zone. We show that its winding over half the Brillouin zone yields the Z2 invariant. To measure this winding, our protocol only requires Bloch oscillations within a single band, supplemented by coherent transitions to a second band which can be realized by lattice-shaking.

 Title: tt* Geometry and a Twistorial Extension of Topological Strings Authors: Vafa, Cumrun Publication: eprint arXiv:1402.2674 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 19 pages Bibliographic Code: 2014arXiv1402.2674V

### Abstract

We extend the recent study of 3d tt* geometry to 5d (4d) N=1 (N=2) supersymmetric theories. We show how the amplitudes of tt* geometry lead to an extension of topological strings and Nekrasov partition functions to twistor space, where the north/south poles of the twistor sphere lead to topological/anti-topological string amplitudes. However, the equator of the twistor sphere is the physical region for the amplitudes, where the unitarity of physical amplitudes is respected. We propose that the amplitudes for Line operators studied by Gaiotto, Moore and Neitzke lead to difference equations for the twistorial topological string partition function, extending the familiar one for the monodromy of Branes in the context of the standard topological strings. This setup unifies tt* geometry, topological strings and the hyperKahler geometry formulated by GMN into a single framework.

 Title: Quantum interference between independent reservoirs in open quantum systems Authors: Chan, Ching-Kit; Lin, Guin-Dar; Yelin, Susanne F.; Lukin, Mikhail D. Publication: eprint arXiv:1402.3289 Publication Date: 02/2014 Origin: ARXIV Keywords: Quantum Physics, Condensed Matter - Quantum Gases Comment: 9 pages, 6 figures Bibliographic Code: 2014arXiv1402.3289C

### Abstract

When a quantum system interacts with multiple reservoirs, the environmental effects are usually treated in an additive manner. We show that this assumption breaks down for non-Markovian environments that have finite memory times. Specifically, we demonstrate that quantum interferences between independent environments can qualitatively modify the dynamics of the physical system. We illustrate this effect with a two level system coupled to two structured photonic reservoirs, discuss its origin using a non-equilibrium diagrammatic technique, and show an example when the application of this interference can result in an improved dark state preparation in a $\lambda$ system.

 Title: The Fates of Mutant Lineages and the Distribution of Fitness Effects of Beneficial Mutations in Laboratory Budding Yeast Populations Authors: Frenkel, Evgeni M.; Good, Benjamin H.; Desai, Michael M. Publication: eprint arXiv:1402.3304 Publication Date: 02/2014 Origin: ARXIV Keywords: Quantitative Biology - Populations and Evolution Comment: doi:10.1534/genetics.113.160069 Bibliographic Code: 2014arXiv1402.3304F

### Abstract

The outcomes of evolution are determined by which mutations occur and fix. In rapidly adapting microbial populations, this process is particularly hard to predict because lineages with different beneficial mutations often spread simultaneously and interfere with one another's fixation. Hence to predict the fate of any individual variant, we must know the rate at which new mutations create competing lineages of higher fitness. Here, we directly measured the effect of this interference on the fates of specific adaptive variants in laboratory Saccharomyces cerevisiae populations and used these measurements to infer the distribution of fitness effects of new beneficial mutations. To do so, we seeded marked lineages with different fitness advantages into replicate populations and tracked their subsequent frequencies for hundreds of generations. Our results illustrate the transition between strongly advantageous lineages which decisively sweep to fixation and more moderately advantageous lineages that are often outcompeted by new mutations arising during the course of the experiment. We developed an approximate likelihood framework to compare our data to simulations and found that the effects of these competing beneficial mutations were best approximated by an exponential distribution, rather than one with a single effect size. We then used this inferred distribution of fitness effects to predict the rate of adaptation in a set of independent control populations. Finally, we discuss how our experimental design can serve as a screen for rare, large-effect beneficial mutations.

 Title: Davies-Gaffney-Grigor'yan Lemma on Graphs Authors: Bauer, Frank; Hua, Bobo; Yau, Shing-Tung Publication: eprint arXiv:1402.3457 Publication Date: 02/2014 Origin: ARXIV Keywords: Mathematics - Differential Geometry Bibliographic Code: 2014arXiv1402.3457B

### Abstract

We prove a variant of the Davies-Gaffney-Grigor'yan Lemma for the continuous time heat kernel on graphs. We use it together with the Li-Yau inequality to obtain strong heat kernel estimates for graphs satisfying the exponential curvature dimension inequality.

 Title: Search for $s$-channel Single Top Quark Production in the Missing Energy Plus Jets Sample using the Full CDF II Data Set Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors Publication: eprint arXiv:1402.3756 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: submitted to Phys. Rev. Lett Bibliographic Code: 2014arXiv1402.3756C

### Abstract

The first search for single top quark production from the exchange of an $s$-channel virtual $W$ boson using events with an imbalance in the total transverse momentum, $b$-tagged jets, and no identified leptons is presented. The full data set collected by the Collider Detector at Fermilab, corresponding to an integrated luminosity of 9.45 fb$^{-1}$ from Fermilab Tevatron proton-antiproton collisions at a center of mass energy of 1.96 TeV, is used. Assuming the electroweak production of top quarks of mass 172.5 GeV/$c^2$ in the $s$-channel, a cross section of $1.12_{-0.57}^{+0.61}$ (stat+syst) pb, with a significance of 1.9 standard deviations, is measured. This measurement is combined with a previous result obtained from events with an imbalance in total transverse momentum, $b$-tagged jets, and exactly one identified lepton, yielding a cross section of $1.36_{-0.32}^{+0.37}$ (stat+syst) pb, with a significance of 4.2 standard deviations.

 Title: Unstable Avoided Crossing in Coupled Spinor Condensates Authors: Bernier, Nathan R.; Dalla Torre, Emanuele G.; Demler, Eugene Publication: eprint arXiv:1402.4487 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases Comment: 5 pages, 3 figures, 1 table. Supplemental Material will be made available online Bibliographic Code: 2014arXiv1402.4487B

### Abstract

We consider the dynamics of a Bose-Einstein condensate with two internal states, coupled through a coherent drive. We focus on a specific quench protocol, in which the sign of the coupling field is suddenly changed. At a mean-field level, the system is transferred from a minimum to a maximum of the coupling energy and can remain dynamically stable, in spite of the development of negative- frequency modes. In the presence of a non-zero detuning between the two states, the "charge" and "spin" modes couple, giving rise to an unstable avoided crossing. This phenomenon is generic to systems with two dispersing modes away from equilibrium and constitutes an example of class-$I_o$ non-equilibrium pattern formation in quantum systems.

 Title: Bond order instabilities in a correlated two-dimensional metal Authors: Allais, Andrea; Bauer, Johannes; Sachdev, Subir Publication: eprint arXiv:1402.4807 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons Comment: 4 pages, 3 figures Bibliographic Code: 2014arXiv1402.4807A

### Abstract

Motivated by recent experimental evidence of charge order in the pseudogap phase of cuprates, we perform a variational analysis of charge-neutral, spin-singlet ordering in metals on the square lattice, using a wavefunction with double occupancy projected out. We examine ordering with and without time-reversal symmetry, with arbitrary wavevector and tunable form factor. Depending on parameters, we find d-wave bond density wave ordering with wavevector either parallel to the lattice generators or diagonally oriented, or a ground state which carries a time reversal-breaking pattern of spontaneous currents.

 Title: The symmetry of charge order in cuprates Authors: Comin, R.; Sutarto, R.; He, F.; da Silva Neto, E.; Chauviere, L.; Frano, A.; Liang, R.; Hardy, W. N.; Bonn, D.; Yoshida, Y.; Eisaki, H.; Hoffman, J. E.; Keimer, B.; Sawatzky, G. A.; Damascelli, A. Publication: eprint arXiv:1402.5415 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons Comment: A high-resolution version with supplementary material can be found at: http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/CDW_symmetry.pdf Bibliographic Code: 2014arXiv1402.5415C

### Abstract

Charge-ordered ground states permeate the phenomenology of 3d-based transition metal oxides, and more generally represent a distinctive hallmark of strongly-correlated states of matter. The recent discovery of charge order in various cuprate families fueled new interest into the role played by this incipient broken symmetry within the complex phase diagram of high-Tc superconductors. Unveiling its origin and nature is key to a microscopic understanding of the normal state, which carries the seeds of unconventional superconductivity. Here we use resonant X-ray scattering to resolve the main characteristics of the charge-modulated state in two cuprate families: Bi2Sr2-xLaxCuO6 (Bi2201) and YBa2Cu3O6+y (YBCO). As a first result, we detect no signatures of spatial modulations along the nodal direction in Bi2201, thus clarifying the inter-unit-cell momentum-structure of the order parameter. In addition, by adopting a special experimental geometry, we also resolve the intra-unit-cell symmetry of the charge ordered state, which is revealed to be predominantly a d-wave bond-order with modulated charges on the O-2p orbitals. These results represent a fundamental advancement in our microscopic description of charge order in cuprates, and provide crucial insights for the understanding of its origin and interplay with superconductivity and magnetism.

 Title: Auxiliary-boson and DMFT studies of bond ordering instabilities of t-J-V models on the square lattice Authors: Allais, Andrea; Bauer, Johannes; Sachdev, Subir Publication: eprint arXiv:1402.6311 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons Comment: 18 pages, 8 figures Bibliographic Code: 2014arXiv1402.6311A

### Abstract

We examine the influence of strong on-site Coulomb interactions on instabilities of the metallic state on the square lattice to general forms of bond order. The Mott correlations are accounted for by the auxiliary-boson method, and by dynamical mean field theory calculations, complementing our recent work (arXiv:1402.4807) using Gutzwiller projected variational wavefunctions. By the present methods, we find that the on-site Mott correlations do not significantly modify the structure of the bond ordering instabilities which preserve time-reversal symmetry, but they do enhance the instability towards time-reversal symmetry breaking "staggered flux" states.

 Title: Singularities and Gauge Theory Phases Authors: Esole, Mboyo; Shao, Shu-Heng; Yau, Shing-Tung Publication: eprint arXiv:1402.6331 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Theory, Mathematics - Algebraic Geometry Comment: 50 pages Bibliographic Code: 2014arXiv1402.6331E

### Abstract

Motivated by M-theory compactification on elliptic Calabi-Yau threefolds, we present a correspondence between networks of small resolutions for singular elliptic fibrations and Coulomb branches of five-dimensional N=1 gauge theories. While resolutions correspond to subchambers of the Coulomb branch, partial resolutions correspond to higher codimension loci at which the Coulomb branch intersects the Coulomb-Higgs branches. Flops between different resolutions are identified with reflections on the Coulomb branch. Physics aside, this correspondence provides an interesting link between elliptic fibrations and representation theory.

 Title: An X-Ray Line from eXciting Dark Matter Authors: Finkbeiner, Douglas P.; Weiner, Neal Publication: eprint arXiv:1402.6671 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Phenomenology, Astrophysics - High Energy Astrophysical Phenomena Comment: 11 pages Bibliographic Code: 2014arXiv1402.6671F

### Abstract

The eXciting Dark Matter (XDM) model was proposed as a mechanism to efficiently convert the kinetic energy (in sufficiently hot environments) of dark matter into e+e- pairs. The standard scenario invokes a doublet of nearly degenerate DM states, and a dark force to mediate a large upscattering cross section between the two. For heavy ($\sim \rm TeV$) DM, the kinetic energy of WIMPs in large (galaxy-sized or larger) halos is capable of producing low-energy positrons. For lighter dark matter, this is kinematically impossible, and the unique observable signature becomes an X-ray line. This variant of XDM is distinctive from other DM X-ray scenarios in that it tends to be most present in more massive, hotter environments, such as clusters, rather than nearby dwarfs, and has different dependencies from decaying models. We find that it is capable of explaining the recently reported X-ray line at 3.56 keV. Thermal models freeze-out as in the normal XDM setup, via annihilations to the light boson $\phi$. For suitable masses the annihilation $\chi \chi \rightarrow \phi \phi$ followed by $\phi \rightarrow SM$ can explain the reported gamma-ray signature from the galactic center. Direct detection is discussed, including the possibility of explaining DAMA via the "Luminous" dark matter approach. Quite generally, the proximity of the 3.56 keV line to the energy scale of DAMA motivates a reexamination of electromagnetic explanations. Other signals, including lepton jets and the modification of cores of dwarf galaxies are also considered.

 Title: The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter Authors: Daylan, Tansu; Finkbeiner, Douglas P.; Hooper, Dan; Linden, Tim; Portillo, Stephen K. N.; Rodd, Nicholas L.; Slatyer, Tracy R. Publication: eprint arXiv:1402.6703 Publication Date: 02/2014 Origin: ARXIV Keywords: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - Galaxy Astrophysics, High Energy Physics - Phenomenology, High Energy Physics - Theory Comment: 26 pages, 28 figures Bibliographic Code: 2014arXiv1402.6703D

### Abstract

Past studies have identified a spatially extended excess of ~1-3 GeV gamma rays from the region surrounding the Galactic Center, consistent with the emission expected from annihilating dark matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails of the point spread function and generate high resolution gamma-ray maps, enabling us to more easily separate the various gamma-ray components. Within these maps, we find the GeV excess to be robust and highly statistically significant, with a spectrum, angular distribution, and overall normalization that is in good agreement with that predicted by simple annihilating dark matter models. For example, the signal is very well fit by a 31-40 GeV dark matter particle annihilating to b quarks with an annihilation cross section of sigma v = (1.4-2.0) x 10^-26 cm^3/s (normalized to a local dark matter density of 0.3 GeV/cm^3). Furthermore, we confirm that the angular distribution of the excess is approximately spherically symmetric and centered around the dynamical center of the Milky Way (within ~0.05 degrees of Sgr A*), showing no sign of elongation along or perpendicular to the Galactic Plane. The signal is observed to extend to at least 10 degrees from the Galactic Center, disfavoring the possibility that this emission originates from millisecond pulsars.

 Title: Chiral Prethermalization in supersonically split condensates Authors: Agarwal, Kartiek; Dalla Torre, Emanuele G.; Rauer, Bernhard; Langen, Tim; Schmiedmayer, Jörg; Demler, Eugene Publication: eprint arXiv:1402.6716 Publication Date: 02/2014 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases Comment: 12 pages, 5 figures Bibliographic Code: 2014arXiv1402.6716A

### Abstract

We study the dynamics of phase relaxation between a pair of one-dimensional condensates created by a supersonic unzipping of a single condensate. We use the Lorentz invariance of the low energy sector of such systems to show that dephasing results in an unusual prethermal state, in which right- and left-moving excitations have different, Doppler-shifted temperatures. The chirality of these modes can be probed experimentally by measuring the interference fringe contrasts with the release point of the split condensates moving at another supersonic velocity. Further, an accelerated motion of the release point can be used to observe a space-like analogue of the Unruh effect. A concrete experimental realization of the quantum zipper for a BEC of trapped atoms on a atom chip is outlined. We interpret these results in the context of the general question of the Lorentz transformation of temperature, and the close analogy with the dipolar anisotropy of the Cosmic Microwave Background.

 Title: Study of Top-Quark Production and Decays involving a Tau Lepton at CDF and Limits on a Charged-Higgs Boson Contribution Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 403 coauthors Publication: eprint arXiv:1402.6728 Publication Date: 02/2014 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: 8 pages, 4 figures submitted to Phys. Rev. Lett Bibliographic Code: 2014arXiv1402.6728C

### Abstract

We present an analysis of top-antitop quark production and decay into a tau lepton, tau neutrino, and bottom quark using data from $9 {\rm fb}^{-1}$ of integrated luminosity at the Collider Detector at Fermilab. Dilepton events, where one lepton is an energetic electron or muon and the other a hadronically-decaying tau lepton, originating from proton-antiproton collisions at $\sqrt{s} = 1.96 TeV$ are used. A top-antitop quark production cross section of $8.1 \pm 2.1 {\rm pb}$ is measured, assuming standard-model top-quark decays. By separately identifying for the first time the single-tau and the ditau components, we measure the branching fraction of the top quark into tau lepton, tau neutrino, and bottom quark to be $(9.6 \pm 2.8) \%$. The branching fraction of top-quark decays into a charged Higgs boson and a bottom quark, which would imply violation of lepton universality, is limited to be less than $5.9 \%$ at $95 \%$ confidence level.

 Title: Mobilization of a trapped non-wetting fluid from a three-dimensional porous medium Authors: Datta, Sujit S.; Ramakrishnan, T. S.; Weitz, David A. Publication: eprint arXiv:1402.6991 Publication Date: 02/2014 Origin: ARXIV Keywords: Physics - Fluid Dynamics, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Soft Condensed Matter, Physics - Geophysics Comment: Physics of Fluids 26, 022002 (2014); doi:10.1063/1.4866641 Bibliographic Code: 2014arXiv1402.6991D

### Abstract

We use confocal microscopy to directly visualize the formation and complex morphologies of trapped non-wetting fluid ganglia within a model 3D porous medium. The wetting fluid continues to flow around the ganglia after they form; this flow is characterized by a capillary number, Ca. We find that the ganglia configurations do not vary for small Ca; by contrast, as Ca is increased above a threshold value, the largest ganglia start to become mobilized and are ultimately removed from the medium. By combining our 3D visualization with measurements of the bulk transport, we show that this behavior can be quantitatively understood by balancing the viscous forces exerted on the ganglia with the pore-scale capillary forces that keep them trapped within the medium. Our work thus helps elucidate the fluid dynamics underlying the mobilization of a trapped non-wetting fluid from a 3D porous medium.

 Title: Scattering resonances and bound states for strongly interacting Rydberg polaritons Authors: Bienias, P.; Choi, S.; Firstenberg, O.; Maghrebi, M. F.; Gullans, M.; Lukin, M. D.; Gorshkov, A. V.; Büchler, H. P. Publication: eprint arXiv:1402.7333 Publication Date: 02/2014 Origin: ARXIV Keywords: Quantum Physics, Physics - Atomic Physics Comment: 6 pages, 2 Figures Bibliographic Code: 2014arXiv1402.7333B

### Abstract

We provide a theoretical framework describing slow-light polaritons interacting via atomic Rydberg states. We use a diagrammatic method to analytically derive the scattering properties of two polaritons. We identify parameter regimes where polariton-polariton interactions are repulsive. Furthermore, in the regime of attractive interactions, we identify multiple two-polariton bound states, calculate their dispersion, and study the resulting scattering resonances. Finally, the two-particle scattering properties allow us to derive the effective low-energy many-body Hamiltonian. This theoretical platform is applicable to ongoing experiments.

 Title: Bacillus spores as building blocks for stimuli-responsive materials and nanogenerators Authors: Chen, Xi; Mahadevan, L.; Driks, Adam; Sahin, Ozgur Publication: Nature Nanotechnology, Volume 9, Issue 2, pp. 137-141 (2014). Publication Date: 02/2014 Origin: NATURE Abstract Copyright: (c) 2014: Nature Publishing Group DOI: 10.1038/nnano.2013.290 Bibliographic Code: 2014NatNa...9..137C

### Abstract

Materials that respond mechanically to external chemical stimuli have applications in biomedical devices, adaptive architectural systems, robotics and energy harvesting. Inspired by biological systems, stimuli-responsive materials have been created that can oscillate, transport fluid, provide homeostasis and undergo complex changes in shape. However, the effectiveness of synthetic stimuli-responsive materials in generating work is limited when compared with mechanical actuators. Here, we show that the mechanical response of Bacillus spores to water gradients exhibits an energy density of more than 10 MJ m-3, which is two orders of magnitude higher than synthetic water-responsive materials. We also identified mutations that can approximately double the energy density of the spores and found that they can self-assemble into dense, submicrometre-thick monolayers on substrates such as silicon microcantilevers and elastomer sheets, creating bio-hybrid hygromorph actuators. To illustrate the potential applications of the spores, we used them to build an energy-harvesting device that can remotely generate electrical power from an evaporating body of water.

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