Faculty Publications: December, 2015

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Title:
Measurement of the production of neighbouring jets in lead-lead collisions at √{sNN} = 2.76 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2876 coauthors
Publication:
Physics Letters B, Volume 751, p. 376-395.
Publication Date:
12/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2015.10.059
Bibliographic Code:
2015PhLB..751..376A

Abstract

This Letter presents measurements of correlated production of nearby jets in Pb+Pb collisions at √{sNN} = 2.76 TeV using the ATLAS detector at the Large Hadron Collider. The measurement was performed using 0.14 nb-1 of data recorded in 2011. The production of correlated jet pairs was quantified using the rate, RΔR, of "neighbouring" jets that accompany "test" jets within a given range of angular distance, ΔR, in the pseudorapidity-azimuthal angle plane. The jets were measured in the ATLAS calorimeter and were reconstructed using the anti-kt algorithm with radius parameters d = 0.2, 0.3, and 0.4. RΔR was measured in different Pb+Pb collision centrality bins, characterized by the total transverse energy measured in the forward calorimeters. A centrality dependence of RΔR is observed for all three jet radii with RΔR found to be lower in central collisions than in peripheral collisions. The ratios formed by the RΔR values in different centrality bins and the values in the 40-80% centrality bin are presented.

 

Title:
Measurement of the branching ratio Γ (Λb0 → ψ (2 S)Λ0) / Γ (Λb0 → J / ψΛ0) with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2850 coauthors
Publication:
Physics Letters B, Volume 751, p. 63-80.
Publication Date:
12/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 The Authors
DOI:
10.1016/j.physletb.2015.10.009
Bibliographic Code:
2015PhLB..751...63A

Abstract

An observation of the Λb0 → ψ (2 S)Λ0 decay and a comparison of its branching fraction with that of the Λb0 → J / ψΛ0 decay has been made with the ATLAS detector in proton-proton collisions at √{ s} = 8 TeV at the LHC using an integrated luminosity of 20.6 fb-1. The J / ψ and ψ (2 S) mesons are reconstructed in their decays to a muon pair, while the Λ0 → pπ- decay is exploited for the Λ0 baryon reconstruction. The Λb0 baryons are reconstructed with transverse momentum pT > 10 GeV and pseudorapidity | η | < 2.1. The measured branching ratio of the Λb0 → ψ (2 S)Λ0 and Λb0 → J / ψΛ0 decays is Γ (Λb0 → ψ (2 S)Λ0) / Γ (Λb0 → J / ψΛ0) = 0.501 ± 0.033 (stat) ± 0.019 (syst), lower than the expectation from the covariant quark model.

 

Title:
Adiabatic isometric mapping algorithm for embedding 2-surfaces in Euclidean 3-space
Authors:
Ray, Shannon; Miller, Warner A.; Alsing, Paul M.; Yau, Shing-Tung
Publication:
Classical and Quantum Gravity, Volume 32, Issue 23, article id. 235012 (2015). (CQGra Homepage)
Publication Date:
12/2015
Origin:
IOP
DOI:
10.1088/0264-9381/32/23/235012
Bibliographic Code:
2015CQGra..32w5012R

Abstract

Alexandrov proved that any simplicial complex homeomorphic to a sphere with strictly non-negative Gaussian curvature at each vertex can be isometrically embedded uniquely in {{{R}}}3 as a convex polyhedron. Due to the nonconstructive nature of his proof, there have yet to be any algorithms, that we know of, that realizes the Alexandrov embedding in polynomial time. Following his proof, we developed the adiabatic isometric mapping (AIM) algorithm. AIM uses a guided adiabatic pull-back procedure on a given polyhedral metric to produce an embedding that approximates the unique Alexandrov polyhedron. Tests of AIM applied to two different polyhedral metrics suggests that its run time is sub cubic with respect to the number of vertices. Although Alexandrov’s theorem specifically addresses the embedding of convex polyhedral metrics, we tested AIM on a broader class of polyhedral metrics that included regions of negative Gaussian curvature. One test was on a surface just outside the ergosphere of a Kerr black hole.

 

Title:
Hypercalibration: A Pan-STARRS1-based recalibration of the Sloan Digital Sky Survey
Authors:
Finkbeiner, Douglas P.; Schlafly, Edward F.; Schlegel, David J.; Padmanabhan, Nikhil; Juric, Mario; Burgett, William S.; Chambers, Kenneth C.; Denneau, Larry; Draper, Peter W.; Flewelling, Heather; Hodapp, Klaus W.; Kaiser, Nick; Magnier, E. A.; Metcalfe, N.; Morgan, Jeffrey S.; Price, Paul A.; Stubbs, Christopher W.; Tonry, John L.
Publication:
eprint arXiv:1512.01214
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics
Comment:
13 pages, 7 figures, ApJ, in press. "Hypercalibration" refers to using repeat measurements of many stars from multiple surveys to constrain calibration parameters
Bibliographic Code:
2015arXiv151201214F

Abstract

We present a recalibration of the Sloan Digital Sky Survey (SDSS) photometry with new flat fields and zero points derived from Pan-STARRS1 (PS1). Using PSF photometry of 60 million stars with $16 < r < 20$, we derive a model of amplifier gain and flat-field corrections with per-run RMS residuals of 3 millimagnitudes (mmag) in $griz$ bands and 15 mmag in $u$ band. The new photometric zero points are adjusted to leave the median in the Galactic North unchanged for compatibility with previous SDSS work. We also identify transient non-photometric periods in SDSS ("contrails") based on photometric deviations co-temporal in SDSS bands. The recalibrated stellar PSF photometry of SDSS and PS1 has an RMS difference of {9,7,7,8} mmag in $griz$, respectively, when averaged over $15'$ regions.

 

Title:
Emergent gauge fields and the high temperature superconductors
Authors:
Sachdev, Subir
Publication:
eprint arXiv:1512.00465
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
16 pages, 11 figures, but only 3 equations. Talk presented at "Unifying physics and technology in light of Maxwell's equations", Discussion Meeting at the Royal Society, London, November 16-17, 2015, celebrating the 150th anniversary of Maxwell's equations. For talk slides, see http://qpt.physics.harvard.edu/talks/royalsociety15.pdf
Bibliographic Code:
2015arXiv151200465S

Abstract

The quantum entanglement of many states of matter can be represented by electric and magnetic fields, much like those found in Maxwell's theory. These fields "emerge" from the quantum structure of the many-electron state, rather than being fundamental degrees of freedom of the vacuum. I review basic aspects of the theory of emergent gauge fields in insulators in an intuitive manner. In metals, Fermi liquid theory relies on adiabatic continuity from the free electron state, and its central consequence is the existence of long-lived electron-like quasiparticles around a Fermi surface enclosing a volume determined by the total density of electrons, via the Luttinger theorem. However long-range entanglement and emergent gauge fields can also be present in metals. I focus on the "fractionalized Fermi liquid" (FL*) state, which also has long-lived electron-like quasiparticles around a Fermi surface; however the Luttinger theorem on the Fermi volume is violated, and this requires the presence of emergent gauge fields, and the associated loss of adiabatic continuity to the free electron state. Finally, I present a brief survey of some recent experiments in the hole-doped cuprate superconductors, and interpret the properties of the pseudogap regime in the framework of the FL* theory.

 

Title:
HARPS-N Observes the Sun as a Star
Authors:
Dumusque, Xavier; Glenday, Alex; Phillips, David F.; Buchschacher, Nicolas; Collier Cameron, Andrew; Cecconi, Massimo; Charbonneau, David; Cosentino, Rosario; Ghedina, Adriano; Latham, David W.; Li, Chih-Hao; Lodi, Marcello; Lovis, Christophe; Molinari, Emilio; Pepe, Francesco; Udry, Stéphane; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald
Publication:
The Astrophysical Journal Letters, Volume 814, Issue 2, article id. L21, 5 pp. (2015). (ApJL Homepage)
Publication Date:
12/2015
Origin:
IOP
Astronomy Keywords:
instrumentation: spectrographs, planets and satellites: detection, techniques: radial velocities
DOI:
10.1088/2041-8205/814/2/L21
Bibliographic Code:
2015ApJ...814L..21D

Abstract

Radial velocity (RV) perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with an astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to RV changes. Over seven days of observing in 2014, we show an average 50 cm s‑1 RV rms over a few hours of observation. After correcting observed radial velocities for spot and plage perturbations using full-disk photometry of the Sun, we lower by a factor of two the weekly RV rms to 60 cm s‑1. The solar telescope is now entering routine operation, and will observe the Sun every clear day for several hours. We will use these radial velocities combined with data from solar satellites to improve our understanding of stellar noise and develop optimal correction methods. If successful, these new methods should enable the detection of Venus over the next two to three years, thus demonstrating the possibility of detecting Earth-twins around other solar-like stars using the RV technique.

 

Title:
BICEP2 III: Instrumental Systematics
Authors:
BICEP2 Collaboration; Ade, P. A. R.; Aikin, R. W.; Barkats, D.; Benton, S. J.; Bischoff, C. A.; Bock, J. J.; Brevik, J. A.; Buder, I.; Bullock, E.; Dowell, C. D.; Duband, L.; Filippini, J. P.; Fliescher, S.; Golwala, S. R.; Halpern, M.; Hasselfield, M.; Hildebrandt, S. R.; Hilton, G. C.; Irwin, K. D.; Karkare, K. S.; Kaufman, J. P.; Keating, B. G.; Kernasovskiy, S. A.; Kovac, J. M.; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Netterfield, C. B.; Nguyen, H. T.; O'Brient, R.; Ogburn, R. W., IV; Orlando, A.; Pryke, C.; Richter, S.; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Sudiwala, R. V.; Teply, G. P.; Tolan, J. E.; Turner, A. D.; Vieregg, A. G.; Wong, C. L.; Yoon, K. W.
Publication:
The Astrophysical Journal, Volume 814, Issue 2, article id. 110, 28 pp. (2015). (ApJ Homepage)
Publication Date:
12/2015
Origin:
IOP
Astronomy Keywords:
cosmic background radiation, cosmology: observations, gravitational waves, inflation, instrumentation: polarimeters, methods: data analysis
DOI:
10.1088/0004-637X/814/2/110
Bibliographic Code:
2015ApJ...814..110B

Abstract

In a companion paper, we have reported a >5σ detection of degree scale B-mode polarization at 150 GHz by the BICEP2 experiment. Here we provide a detailed study of potential instrumental systematic contamination to that measurement. We focus extensively on spurious polarization that can potentially arise from beam imperfections. We present a heuristic classification of beam imperfections according to their symmetries and uniformities, and discuss how resulting contamination adds or cancels in maps that combine observations made at multiple orientations of the telescope about its boresight axis. We introduce a technique, which we call "deprojection," for filtering the leading order beam-induced contamination from time-ordered data, and show that it reduces power in BICEP2's actual and null-test BB spectra consistent with predictions using high signal-to-noise beam shape measurements. We detail the simulation pipeline that we use to directly simulate instrumental systematics and the calibration data used as input to that pipeline. Finally, we present the constraints on BB contamination from individual sources of potential systematics. We find that systematics contribute BB power that is a factor of ∼10× below BICEP2's three-year statistical uncertainty, and negligible compared to the observed BB signal. The contribution to the best-fit tensor/scalar ratio is at a level equivalent to r = (3-6) × 10-3.

 

Title:
Supercal: Cross-calibration of Multiple Photometric Systems to Improve Cosmological Measurements with Type Ia Supernovae
Authors:
Scolnic, D.; Casertano, S.; Riess, A.; Rest, A.; Schlafly, E.; Foley, R. J.; Finkbeiner, D.; Tang, C.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Huber, M. E.; Kaiser, N.; Kudritzki, R. P.; Magnier, E. A.; Metcalfe, N.; Stubbs, C. W.
Publication:
The Astrophysical Journal, Volume 815, Issue 2, article id. 117, 15 pp. (2015). (ApJ Homepage)
Publication Date:
12/2015
Origin:
IOP
Astronomy Keywords:
dark energy, supernovae: general, surveys
DOI:
10.1088/0004-637X/815/2/117
Bibliographic Code:
2015ApJ...815..117S

Abstract

Current cosmological analyses, which use Type Ia supernova observations, combine supernova (SN) samples to expand the redshift range beyond that of a single sample and increase the overall sample size. The inhomogeneous photometric calibration between different SN samples is one of the largest systematic uncertainties of the cosmological parameter estimation. To place these different samples on a single system, analyses currently use observations of a small sample of very bright flux standards on the Hubble Space Telescope system. We propose a complementary method, called "Supercal," in which we use measurements of secondary standards in each system, compare these to measurements of the same stars in the Pan-STARRS1 (PS1) system, and determine the offsets for each system relative to PS1, placing all SN observations on a single, consistent photometric system. PS1 has observed 3π of the sky and has a relative calibration of better than 5 mmag (for ˜15 < griz < 21 mag), making it an ideal reference system. We use this process to recalibrate optical observations taken by the following SN samples: PS1, Supernova Legacy Survey, SDSS, CSP, and CfA1-4. We measure discrepancies on average of 10 mmag, but up to 35 mmag, in various optical passbands. We find that correcting for these differences changes the recovered values for the dark energy equation of state parameter, w, by an average of 2.6%. This change is roughly half the size of current statistical constraints on w. The size of this effect strongly depends on the error in the B - V calibration of the low-z surveys. The Supercal method will allow future analyses to tie past samples to the best calibrated sample.

 

Title:
Interferometric Measurements of Many-body Topological Invariants using Mobile Impurities
Authors:
Grusdt, Fabian; Yao, Norman Y.; Abanin, Dmitry A.; Fleischhauer, Michael; Demler, Eugene A.
Publication:
eprint arXiv:1512.03407
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Other Condensed Matter, Quantum Physics
Comment:
11 pages, 3 figures, 3 pages Supplementary
Bibliographic Code:
2015arXiv151203407G

Abstract

Topological quantum phases cannot be characterized by Ginzburg-Landau type order parameters, and are instead described by non-local topological invariants. Experimental platforms capable of realizing such exotic states now include "synthetic" many-body systems such as ultracold atoms or photons. Unique tools available in these systems enable a new characterization of strongly correlated many-body states. Here we propose a general scheme for detecting topological order using interferometric measurements of elementary excitations. The key ingredient is the use of mobile impurities which bind to quasiparticles of a host many-body system. Specifically we show how fractional charges can be probed in the bulk of fractional quantum Hall systems. We demonstrate that combining Ramsey interference with Bloch oscillations can be used to measure Chern numbers of individual quasiparticles, which gives a direct probe of their fractional charges. We discuss possible extensions of our method to other topological many-body systems, such as spin liquids.

 

Title:
Holographic Maps of Quasiparticle Interference
Authors:
Dalla Torre, Emanuele G.; He, Yang; Demler, Eugene
Publication:
eprint arXiv:1512.03456
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Comment:
10+14 pages, 5+9 figures
Bibliographic Code:
2015arXiv151203456D

Abstract

The analysis of Fourier-transformed scanning-tunneling-microscopy (STM) images with subatomic resolution is a common tool for studying properties of quasiparticle excitations in strongly correlated materials. While Fourier amplitudes are generally complex valued, earlier analysis mostly considered only their absolute values. Their complex phases were deemed random, and thus irrelevant, due to the unknown positions of impurities in the sample. Here we show how to factor out these random phases by analysing overlaps between Fourier amplitudes that differ by reciprocal lattice vectors. The resulting holographic maps provide important and previously-unknown information about the electronic structures of materials. When applied to superconducting cuprates, our method solves a long-standing puzzle of the dichotomy between equivalent wavevectors. We show that $d$-wave Wannier functions of the conduction band provide a natural explanation for experimental results that were interpreted as evidence for competing unconventional charge modulations. Our work opens a new pathway to identify the nature of electronic states in STM measurements.

 

Title:
Superconducting pairing in resonant inelastic X-ray scattering
Authors:
Shi, Yifei; Benjamin, David; Demler, Eugene; Klich, Israel
Publication:
eprint arXiv:1512.03804
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Bibliographic Code:
2015arXiv151203804S

Abstract

We develop a method to study the effect of the superconducting transition on resonant inelastic X-ray scattering (RIXS) signal in superconductors with an order parameter with an arbitrary symmetry within a quasiparticle approach. As an example, we compare the direct RIXS signal below and above the superconducting transition for p-wave type order parameters. For a p-wave order parameter with a nodal line, we show that, counterintuitively, the effect of the gap is most noticeable for momentum transfers in the nodal direction. This phenomenon may be naturally explained as a type of nesting effect.

 

Title:
Coherent optical emitters in diamond nanostructures via ion implantation
Authors:
Evans, Ruffin E.; Sipahigil, Alp; Sukachev, Denis D.; Zibrov, Alexander S.; Lukin, Mikhail D.
Publication:
eprint arXiv:1512.03820
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Comment:
7 pages, 3 figures. (v2) Added supplemental material as an ancillary file, fixed typos in references
Bibliographic Code:
2015arXiv151203820E

Abstract

The negatively-charged silicon-vacancy ($\mathrm{SiV}^{-}$) center in diamond is a bright source of indistinguishable single photons and a useful resource in quantum information protocols. Until now, $\mathrm{SiV}^{-}$ centers with narrow optical linewidths and small inhomogeneous distributions of $\mathrm{SiV}^{-}$ transition frequencies have only been reported in samples doped with silicon during diamond growth. We present a technique for producing implanted $\mathrm{SiV}^{-}$ centers with nearly lifetime-limited optical linewidths and a small inhomogeneous distribution. These properties persist after nanofabrication, paving the way for incorporation of high-quality $\mathrm{SiV}^{-}$ centers into nanophotonic devices.

 

Title:
Diamond optomechanical crystals
Authors:
Burek, Michael J.; Cohen, Justin D.; Meenehan, Seán M.; Ruelle, Thibaud; Meesala, Srujan; Rochman, Jake; Atikian, Haig A.; Markham, Matthew; Twitchen, Daniel J.; Lukin, Mikhail D.; Painter, Oskar; Lončar, Marko
Publication:
eprint arXiv:1512.04166
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Bibliographic Code:
2015arXiv151204166B

Abstract

Cavity-optomechanical systems realized in single-crystal diamond are poised to benefit from its extraordinary material properties, including low mechanical dissipation and wide optical transparency window. Diamond is also rich in optically active defects, such as the nitrogen-vacancy (NV) center, which behave as atom-like systems in the solid state. Predictions and observations of coherent coupling of the NV electronic spin to phonons via lattice strain has motivated the development of diamond nanomechanical devices aimed at realization of hybrid quantum systems, in which phonons provide an interface with diamond spins. In this work, we demonstrate a device platform to enable such applications: diamond optomechanical crystals (OMCs), where the co-localization of ~ 200 THz photons and ~ 6 GHz phonons in a quasi-periodic diamond nanostructure leads to coupling of an optical cavity field to a mechanical mode via the radiation pressure of light. In contrast to other material systems, diamond OMCs operating in the resolved sideband regime possess large intracavity photon capacity (> 10$^5$) and sufficient optomechanical coupling rate to exceed a cooperativity of ~ 1 at room temperature and realize large amplitude optomechanical self-oscillations. Strain-mediated coupling of the high frequency (~ GHz) mechanical modes of these devices to the electronic and spin levels of diamond color centers has the potential to reach the strong spin-phonon coupling regime, and enable a coherent interface with diamond qubits for applications in quantum-nonlinear optomechanics.

 

Title:
SUSY's Ladder: Reframing Sequestering at Large Volume
Authors:
Reece, Matthew; Xue, Wei
Publication:
eprint arXiv:1512.04941
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Theory
Comment:
33 pages, 4 figures
Bibliographic Code:
2015arXiv151204941R

Abstract

Theories with approximate no-scale structure, such as the Large Volume Scenario, have a distinctive hierarchy of multiple mass scales in between TeV gaugino masses and the Planck scale, which we call SUSY's Ladder. This is a particular realization of Split Supersymmetry in which the same small parameter suppresses gaugino masses relative to scalar soft masses, scalar soft masses relative to the gravitino mass, and the UV cutoff or string scale relative to the Planck scale. This scenario has many phenomenologically interesting properties, and can avoid dangers including the gravitino problem, flavor problems, and the moduli-induced LSP problem that plague other supersymmetric theories. We study SUSY's Ladder using a superspace formalism that makes the mysterious cancelations in previous computations manifest. This opens the possibility of a consistent effective field theory understanding of the phenomenology of these scenarios, based on power-counting in the small ratio of string to Planck scales. We also show that four-dimensional theories with approximate no-scale structure enforced by a single volume modulus arise only from two special higher-dimensional theories: five-dimensional supergravity and ten-dimensional type IIB supergravity. This gives a phenomenological argument in favor of ten dimensional ultraviolet physics which is different from standard arguments based on the consistency of superstring theory.

 

Title:
Localization in non-Hermitian chains with excitatory/inhibitory connections
Authors:
Amir, Ariel; Hatano, Naomichi; Nelson, David R.
Publication:
eprint arXiv:1512.05478
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Mathematical Physics, Quantitative Biology - Neurons and Cognition
Bibliographic Code:
2015arXiv151205478A

Abstract

We explore the spectra and localization properties of the N-site banded one-dimensional non-Hermitian random matrices that arise naturally in sparse neural networks. Approximately equal numbers of random excitatory and inhibitory connections lead to spatially localized eigenfunctions, and an intricate eigenvalue spectrum in the complex plane that controls the spontaneous activity and induced response. A finite fraction of the eigenvalues condense onto the real or imaginary axes. For large N, the spectrum has remarkable symmetries not only with respect to reflections across the real and imaginary axes, but also with respect to 90 degree rotations, with an unusual anisotropic divergence in the localization length near the origin. When chains with periodic boundary conditions become directed, with a systematic directional bias superimposed on the randomness, a hole centered on the origin opens up in the density-of-states in the complex plane. All states are extended on the rim of this hole, while the localized eigenvalues outside the hole are unchanged. The g-dependent shape of this hole tracks the g=0 contours of constant localization length. We treat the large-N limit by a combination of direct numerical diagonalization and using transfer matrices, an approach that allows us to exploit an electrostatic analogy connecting the "charges" embodied in the eigenvalue distribution with the contours of constant localization length. We show that similar results are obtained for more realistic neural networks that obey "Dale's Law" (each site is purely excitatory or inhibitory), and conclude with perturbation theory results that describe the limit of large bias g, when all states are extended. Related problems arise in random ecological networks and in chains of artificial cells with randomly coupled gene expression patterns.

 

Title:
Experimental Considerations Motivated by the Diphoton Excess at the LHC
Authors:
Agrawal, Prateek; Fan, JiJi; Heidenreich, Ben; Reece, Matthew; Strassler, Matthew
Publication:
eprint arXiv:1512.05775
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Experiment
Bibliographic Code:
2015arXiv151205775A

Abstract

We consider the immediate or near-term experimental opportunities offered by some scenarios that could explain the new diphoton excess at the LHC. If the excess is due to a new particle $X_s$ at 750 GeV, additional new particles are required, providing further signals. If connected with naturalness, the $X_s$ may be produced in top partner decays. Then a $t'\bar t'$ signal, with $t'\to t X_s$ and $X_s\to gg$ dominantly, might be discovered by reinterpreting 13 TeV SUSY searches in multijet events with low MET and/or a lepton. If $X_s$ is a bound state of quirks, the signal events may be accompanied by an unusual number of soft tracks or soft jets. Other resonances including dilepton and photon+jet as well as dijet may lie at or above this mass, and signatures of hidden glueballs might also be observable. If the "photons" in the excess are actually long-lived particles decaying to photon pairs or to electron pairs, there are opportunities for detecting overlapping photons and/or unusual patterns of apparent photon-conversions in either $X_s$ or 125 GeV Higgs decays. There is also the possibility of events with a hard "photon" recoiling against a narrow isolated HCAL-only "jet", which, after the jet's energy is corrected for its electromagnetic origin, would show a peak at 750 GeV.

 

Title:
Stealth Supersymmetry Simplified
Authors:
Fan, JiJi; Krall, Rebecca; Pinner, David; Reece, Matthew; Ruderman, Joshua T.
Publication:
eprint arXiv:1512.05781
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Experiment
Comment:
14 pages plus appendices
Bibliographic Code:
2015arXiv151205781F

Abstract

In Stealth Supersymmetry, bounds on superpartners from direct searches can be notably weaker than in standard supersymmetric scenarios, due to suppressed missing energy. We present a set of simplified models of Stealth Supersymmetry that motivate 13 TeV LHC searches. We focus on simplified models within the Natural Supersymmetry framework, in which the gluino, stop, and Higgsino are assumed to be lighter than other superpartners. Our simplified models exhibit novel decay patterns that differ significantly from topologies of the Minimal Supersymmetric Standard Model, with and without $R$-parity. We determine limits on stops and gluinos from searches at the 8 TeV LHC. Existing searches constitute a powerful probe of Stealth Supersymmetry gluinos with certain topologies. However, we identify simplified models where the gluino can be considerably lighter than 1 TeV. Stops are significantly less constrained in Stealth Supersymmetry than the MSSM, and we have identified novel stop decay topologies that are completely unconstrained by existing LHC searches.

 

Title:
Optimal switching strategies for stochastic geocentric/egocentric navigation
Authors:
Peleg, O.; Mahadevan, L.
Publication:
eprint arXiv:1512.06123
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
Physics - Biological Physics, Condensed Matter - Soft Condensed Matter, Statistics - Applications
Bibliographic Code:
2015arXiv151206123P

Abstract

Animals use a combination of egocentric navigation driven by the internal integration of environmental cues, interspersed with geocentric course correction and reorientation, often with uncertainty in sensory acquisition of information, planning and execution. Inspired directly by observations of dung beetle navigational strategies that show switching between geocentric and egocentric strategies, we consider the question of optimal strategies for the navigation of an agent along a preferred direction in the presence of multiple sources of noise. We address this using a model that takes the form of a correlated random walk at short time scales that is interspersed with reorientation events that yields a biased random walks at long time scales. We identify optimal alternation schemes and characterize their robustness in the context of noisy sensory acquisition, and performance errors linked with variations in environmental conditions and agent-environment interactions.

 

Title:
Relative entropy equals bulk relative entropy
Authors:
Jafferis, Daniel L.; Lewkowycz, Aitor; Maldacena, Juan; Suh, S. Josephine
Publication:
eprint arXiv:1512.06431
Publication Date:
12/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology, Quantum Physics
Comment:
23 pages, 3 figures
Bibliographic Code:
2015arXiv151206431J

Abstract

We consider the gravity dual of the modular Hamiltonian associated to a general subregion of a boundary theory. We use it to argue that the relative entropy of nearby states is given by the relative entropy in the bulk, to leading order in the bulk gravitational coupling. We also argue that the boundary modular flow is dual to the bulk modular flow in the entanglement wedge, with implications for entanglement wedge reconstruction.

 

Title:
Elastic Cheerios effect: Self-assembly of cylinders on a soft solid
Authors:
Chakrabarti, Aditi; Ryan, Louis; Chaudhury, Manoj K.; Mahadevan, L.
Publication:
Europhysics Letters, Volume 112, Issue 5, article id. 54001 (2015).
Publication Date:
12/2015
Origin:
IOP
DOI:
10.1209/0295-5075/112/54001
Bibliographic Code:
2015EL....11254001C

Abstract

A rigid cylinder placed on a soft gel deforms its surface. When multiple cylinders are placed on the surface, they interact with each other via the topography of the deformed gel which serves as an energy landscape; as they move, the landscape changes which in turn changes their interaction. We use a combination of experiments, simple scaling estimates and numerical simulations to study the self-assembly of cylinders in this elastic analog of the "Cheerios Effect", which describes capillary interactions on a fluid interface. Our results show that the effective two-body interaction can be well described by an exponential attraction potential as a result of which the dynamics also show an exponential behavior with respect to the separation distance. When many cylinders are placed on the gel, the cylinders cluster together if they are not too far apart; otherwise their motion gets elastically arrested.


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