Faculty Publications: November, 2015

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Title:
Absence of Disorder-Driven Metal-Insulator Transitions in Simple Holographic Models
Authors:
Grozdanov, Sašo; Lucas, Andrew; Sachdev, Subir; Schalm, Koenraad
Publication:
Physical Review Letters, Volume 115, Issue 22, id.221601 (PhRvL Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Gauge/string duality, Disordered solids
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.115.221601
Bibliographic Code:
2015PhRvL.115v1601G

Abstract

We study electrical transport in a strongly coupled strange metal in two spatial dimensions at finite temperature and charge density, holographically dual to the Einstein-Maxwell theory in an asymptotically four-dimensional anti-de Sitter space spacetime, with arbitrary spatial inhomogeneity, up to mild assumptions including emergent isotropy. In condensed matter, these are candidate models for exotic strange metals without long-lived quasiparticles. We prove that the electrical conductivity is bounded from below by a universal minimal conductance: the quantum critical conductivity of a clean, charge-neutral plasma. Beyond nonperturbatively justifying mean-field approximations to disorder, our work demonstrates the practicality of new hydrodynamic insight into holographic transport.

 

Title:
Prethermal Floquet Steady States and Instabilities in the Periodically Driven, Weakly Interacting Bose-Hubbard Model
Authors:
Bukov, Marin; Gopalakrishnan, Sarang; Knap, Michael; Demler, Eugene
Publication:
Physical Review Letters, Volume 115, Issue 20, id.205301 (PhRvL Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Bose-Einstein condensates in optical potentials, Nonlinear dynamics and chaos, Quantum transport, Nonequilibrium and irreversible thermodynamics
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.115.205301
Bibliographic Code:
2015PhRvL.115t5301B

Abstract

We explore prethermal Floquet steady states and instabilities of the weakly interacting two-dimensional Bose-Hubbard model subject to periodic driving. We develop a description of the nonequilibrium dynamics, at arbitrary drive strength and frequency, using a weak-coupling conserving approximation. We establish the regimes in which conventional (zero-momentum) and unconventional [(π ,π )-momentum] condensates are stable on intermediate time scales. We find that condensate stability is enhanced by increasing the drive strength, because this decreases the bandwidth of quasiparticle excitations and thus impedes resonant absorption and heating. Our results are directly relevant to a number of current experiments with ultracold bosons.

 

Title:
Commentary: The social science of creativity and research practice: Physical scientists, take notice
Authors:
Odumosu, Toluwalogo; Tsao, Jeffrey Y.; Narayanamurti, Venkatesh
Publication:
Physics Today, vol. 68, issue 11, pp. 8-9
Publication Date:
11/2015
Origin:
CROSSREF
DOI:
10.1063/PT.3.2959
Bibliographic Code:
2015PhT....68k...8O

Abstract

Not Available

 

Title:
Study of the energy dependence of the underlying event in proton-antiproton collisions
Authors:
Aaltonen, T.; Albrow, M.; Amerio, S.;... Franklin, M.;... and 400 coauthors
Publication:
Physical Review D, Volume 92, Issue 9, id.092009 (PhRvD Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Production, Electrons, Muons
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevD.92.092009
Bibliographic Code:
2015PhRvD..92i2009A

Abstract

We study charged particle production (pT>0.5 GeV /c , |η |<0.8 ) in proton-antiproton collisions at total center-of-mass energies √{s }=300 GeV , 900 GeV, and 1.96 TeV. We use the direction of the charged particle with the largest transverse momentum in each event to define three regions of η -ϕ space: "toward", "away", and "transverse." The average number and the average scalar pT sum of charged particles in the transverse region are sensitive to the modeling of the "underlying event." The transverse region is divided into a MAX and MIN transverse region, which helps separate the "hard component" (initial and final-state radiation) from the "beam-beam remnant" and multiple parton interaction components of the scattering. The center-of-mass energy dependence of the various components of the event is studied in detail. The data presented here can be used to constrain and improve QCD Monte Carlo models, resulting in more precise predictions at the LHC energies of 13 and 14 TeV.

 

Title:
Searches for Higgs boson pair production in the h h →b b τ τ , γ γ W W* , γ γ b b , b b b b channels with the ATLAS detector
Authors:

Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2864 coauthors

Publication:
Physical Review D, Volume 92, Issue 9, id.092004 (PhRvD Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Extensions of electroweak Higgs sector, Standard-model Higgs bosons
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.92.092004
Bibliographic Code:
2015PhRvD..92i2004A

Abstract

Searches for both resonant and nonresonant Higgs boson pair production are performed in the h h →b b τ τ , γ γ W W* final states using 20.3 fb-1 of p p collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the Large Hadron Collider. No evidence of their production is observed and 95% confidence-level upper limits on the production cross sections are set. These results are then combined with the published results of the h h →γ γ b b , b b b b analyses. An upper limit of 0.69 (0.47) pb on the nonresonant h h production is observed (expected), corresponding to 70 (48) times the SM g g →h h cross section. For production via narrow resonances, cross-section limits of h h production from a heavy Higgs boson decay are set as a function of the heavy Higgs boson mass. The observed (expected) limits range from 2.1 (1.1) pb at 260 GeV to 0.011 (0.018) pb at 1000 GeV. These results are interpreted in the context of two simplified scenarios of the Minimal Supersymmetric Standard Model.

 

Title:
Search for new light gauge bosons in Higgs boson decays to four-lepton final states in p p collisions at √{s }=8 TeV with the ATLAS detector at the LHC
Authors:

Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2821 coauthors

Publication:
Physical Review D, Volume 92, Issue 9, id.092001 (PhRvD Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Applications of electroweak models to specific processes, Extensions of electroweak Higgs sector, Supersymmetric models, Production
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.92.092001
Bibliographic Code:
2015PhRvD..92i2001A

Abstract

This paper presents a search for Higgs bosons decaying to four leptons, either electrons or muons, via one or two light exotic gauge bosons Zd, H →Z Zd→4 ℓ or H →ZdZd →4 ℓ. The search was performed using p p collision data corresponding to an integrated luminosity of about 20 fb-1 at the center-of-mass energy of √{s }=8 TeV recorded with the ATLAS detector at the Large Hadron Collider. The observed data are well described by the Standard Model prediction. Upper bounds on the branching ratio of H →Z Zd→4 ℓ and on the kinetic mixing parameter between the Zd and the Standard Model hypercharge gauge boson are set in the range (1 - 9 )×1 0-5 and (4 - 17 )×1 0-2 respectively, at 95% confidence level assuming the Standard Model branching ratio of H →Z Z*→4 ℓ, for Zd masses between 15 and 55 GeV. Upper bounds on the effective mass mixing parameter between the Z and the Zd are also set using the branching ratio limits in the H →Z Zd→4 ℓ search, and are in the range (1.5 - 8.7)×1 0-4 for 15 <mZd<35 GeV. Upper bounds on the branching ratio of H →ZdZd→4 ℓ and on the Higgs portal coupling parameter, controlling the strength of the coupling of the Higgs boson to dark vector bosons are set in the range (2 - 3 )×10-5 and (1 - 10 )×10-4 respectively, at 95% confidence level assuming the Standard Model Higgs boson production cross sections, for Zd masses between 15 and 60 GeV.

 

Title:
Ab initio tight-binding Hamiltonian for transition metal dichalcogenides
Authors:
Fang, Shiang; Kuate Defo, Rodrick; Shirodkar, Sharmila N.; Lieu, Simon; Tritsaris, Georgios A.; Kaxiras, Efthimios
Publication:
Physical Review B, Volume 92, Issue 20, id.205108 (PhRvB Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Methods of electronic structure calculations, Electronic structure of nanoscale materials: clusters nanoparticles nanotubes and nanocrystals, Multilayers superlattices heterostructures, Other inorganic semiconductors
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.92.205108
Bibliographic Code:
2015PhRvB..92t5108F

Abstract

We present an accurate ab initio tight-binding Hamiltonian for the transition metal dichalcogenides, MoS2, MoSe2, WS2, WSe2, with a minimal basis (the d orbitals for the metal atoms and p orbitals for the chalcogen atoms) based on a transformation of the Kohn-Sham density functional theory Hamiltonian to a basis of maximally localized Wannier functions. The truncated tight-binding Hamiltonian, with only on-site, first, and partial second neighbor interactions, including spin-orbit coupling, provides a simple physical picture and the symmetry of the main band-structure features. Interlayer interactions between adjacent layers are modeled by transferable hopping terms between the chalcogen p orbitals. The full-range tight-binding Hamiltonian can be reduced to hybrid-orbital k .p effective Hamiltonians near the band extrema that capture important low-energy excitations. These ab initio Hamiltonians can serve as the starting point for applications to interacting many-body physics including optical transitions and Berry curvature of bands, of which we give some examples.

 

Title:
1 /f α noise and generalized diffusion in random Heisenberg spin systems
Authors:
Agarwal, Kartiek; Demler, Eugene; Martin, Ivar
Publication:
Physical Review B, Volume 92, Issue 18, id.184203 (PhRvB Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Renormalization group methods, Quantized spin models, Disordered structures, amorphous and glassy solids, Superconducting quantum interference devices
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.92.184203
Bibliographic Code:
2015PhRvB..92r4203A

Abstract

We study the "flux-noise" spectrum of random-bond quantum Heisenberg spin systems using a real-space renormalization group (RSRG) procedure that accounts for both the renormalization of the system Hamiltonian and of a generic probe that measures the noise. For spin chains, we find that the dynamical structure factor Sq(f ) , at finite wave vector q , exhibits a power-law behavior both at high and low frequencies f , with exponents that are connected to one another and to an anomalous dynamical exponent through relations that differ at T =0 and T =∞ . The low-frequency power-law behavior of the structure factor is inherited by any generic probe with a finite bandwidth and is of the form 1 /fα with 0.5 <α <1 . An analytical calculation of the structure factor, assuming a limiting distribution of the RG flow parameters (spin size, length, bond strength) confirms numerical findings. More generally, we demonstrate that this form of the structure factor, at high temperatures, is a manifestation of anomalous diffusion which directly follows from a generalized spin-diffusion propagator. We also argue that 1 /f -noise is intimately connected to many-body-localization at finite temperatures. In two dimensions, the RG procedure is less reliable; however, it becomes convergent for quasi-one-dimensional geometries where we find that one-dimensional 1 /fα behavior is recovered at low frequencies; the latter configurations are likely representative of paramagnetic spin networks that produce 1 /fα noise in SQUIDs.

 

Title:
Fluctuating orders and quenched randomness in the cuprates
Authors:
Nie, Laimei; Sierens, Lauren E. Hayward; Melko, Roger G.; Sachdev, Subir; Kivelson, Steven A.
Publication:
Physical Review B, Volume 92, Issue 17, id.174505 (PhRvB Homepage)
Publication Date:
11/2015
Origin:
APS
PACS Keywords:
Cuprate superconductors, Charge-density-wave systems
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.92.174505
Bibliographic Code:
2015PhRvB..92q4505N

Abstract

We study a quasi-two-dimensional classical Landau-Ginzburg-Wilson effective field theory in the presence of quenched disorder in which incommensurate charge-density wave and superconducting orders are intertwined. The disorder precludes long-range charge-density wave order, but not superconducting or nematic order. We select three representative sets of input parameters and compute the corresponding charge-density wave structure factors using both large-N techniques and classical Monte Carlo simulations. Where nematicity and superconductivity coexist at low temperature, the peak height of the charge-density wave structure factor decreases monotonically as a function of increasing temperature, unlike what is seen in x-ray experiments on YBa2Cu3O6 +x . Conversely, where the thermal evolution of the charge-density wave structure factor qualitatively agrees with experiments, the nematic correlation length, computed to one-loop order, is shorter than the charge-density wave correlation length.

 

Title:
Measurement of colour flow with the jet pull angle in t t bar events using the ATLAS detector at √{ s} = 8 TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2845 coauthors
Publication:
Physics Letters B, Volume 750, p. 475-493.
Publication Date:
11/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2015.09.051
Bibliographic Code:
2015PhLB..750..475A

Abstract

The distribution and orientation of energy inside jets is predicted to be an experimental handle on colour connections between the hard-scatter quarks and gluons initiating the jets. This Letter presents a measurement of the distribution of one such variable, the jet pull angle. The pull angle is measured for jets produced in t t bar events with one W boson decaying leptonically and the other decaying to jets using 20.3 fb-1 of data recorded with the ATLAS detector at a centre-of-mass energy of √{ s} = 8 TeV at the LHC. The jet pull angle distribution is corrected for detector resolution and acceptance effects and is compared to various models.

 

Title:
Measurement of transverse energy-energy correlations in multi-jet events in pp collisions at √{ s} = 7 TeV using the ATLAS detector and determination of the strong coupling constant αs (mZ)
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2851 coauthors
Publication:
Physics Letters B, Volume 750, p. 427-447.
Publication Date:
11/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2015.09.050
Bibliographic Code:
2015PhLB..750..427A

Abstract

High transverse momentum jets produced in pp collisions at a centre of mass energy of 7 TeV are used to measure the transverse energy-energy correlation function and its associated azimuthal asymmetry. The data were recorded with the ATLAS detector at the LHC in the year 2011 and correspond to an integrated luminosity of 158 pb-1. The selection criteria demand the average transverse momentum of the two leading jets in an event to be larger than 250 GeV. The data at detector level are well described by Monte Carlo event generators. They are unfolded to the particle level and compared with theoretical calculations at next-to-leading-order accuracy. The agreement between data and theory is good and provides a precision test of perturbative Quantum Chromodynamics at large momentum transfers. From this comparison, the strong coupling constant given at the Z boson mass is determined to be αs (mZ) = 0.1173 ± 0.0010 (exp.) -0.0026+0.0065 (theo.).

 

Title:
On-chip zero-index metamaterials
Authors:
Li, Yang; Kita, Shota; Muñoz, Philip; Reshef, Orad; Vulis, Daryl I.; Yin, Mei; Lončar, Marko; Mazur, Eric
Publication:
Nature Photonics, Volume 9, Issue 11, pp. 738-742 (2015).
Publication Date:
11/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group
DOI:
10.1038/nphoton.2015.198
Bibliographic Code:
2015NaPho...9..738L

Abstract

Metamaterials with a refractive index of zero exhibit physical properties such as infinite phase velocity and wavelength. However, there is no way to implement these materials on a photonic chip, restricting the investigation and application of zero-index phenomena to simple shapes and small scales. We designed and fabricated an on-chip integrated metamaterial with a refractive index of zero in the optical regime. Light refracts perpendicular to the facets of a prism made of this metamaterial, directly demonstrating that the index of refraction is zero. The metamaterial consists of low-aspect-ratio silicon pillar arrays embedded in a polymer matrix and clad by gold films. This structure can be fabricated using standard planar processes over a large area in arbitrary shapes and can efficiently couple to photonic integrated circuits and other optical elements. This novel on-chip metamaterial platform opens the door to exploring the physics of zero index and its applications in integrated optics.

 

Title:
The 2015 super-resolution microscopy roadmap
Authors:
Hell, Stefan W.; Sahl, Steffen J.; Bates, Mark; Zhuang, Xiaowei; Heintzmann, Rainer; Booth, Martin J.; Bewersdorf, Joerg; Shtengel, Gleb; Hess, Harald; Tinnefeld, Philip; Honigmann, Alf; Jakobs, Stefan; Testa, Ilaria; Cognet, Laurent; Lounis, Brahim; Ewers, Helge; Davis, Simon J.; Eggeling, Christian; Klenerman, David; Willig, Katrin I.; Vicidomini, Giuseppe; Castello, Marco; Diaspro, Alberto; Cordes, Thorben
Publication:
Journal of Physics D: Applied Physics, Volume 48, Issue 44, article id. 443001 (2015).
Publication Date:
11/2015
Origin:
IOP
DOI:
10.1088/0022-3727/48/44/443001
Bibliographic Code:
2015JPhD...48R3001H

Abstract

Far-field optical microscopy using focused light is an important tool in a number of scientific disciplines including chemical, (bio)physical and biomedical research, particularly with respect to the study of living cells and organisms. Unfortunately, the applicability of the optical microscope is limited, since the diffraction of light imposes limitations on the spatial resolution of the image. Consequently the details of, for example, cellular protein distributions, can be visualized only to a certain extent. Fortunately, recent years have witnessed the development of ‘super-resolution’ far-field optical microscopy (nanoscopy) techniques such as stimulated emission depletion (STED), ground state depletion (GSD), reversible saturated optical (fluorescence) transitions (RESOLFT), photoactivation localization microscopy (PALM), stochastic optical reconstruction microscopy (STORM), structured illumination microscopy (SIM) or saturated structured illumination microscopy (SSIM), all in one way or another addressing the problem of the limited spatial resolution of far-field optical microscopy. While SIM achieves a two-fold improvement in spatial resolution compared to conventional optical microscopy, STED, RESOLFT, PALM/STORM, or SSIM have all gone beyond, pushing the limits of optical image resolution to the nanometer scale. Consequently, all super-resolution techniques open new avenues of biomedical research. Because the field is so young, the potential capabilities of different super-resolution microscopy approaches have yet to be fully explored, and uncertainties remain when considering the best choice of methodology. Thus, even for experts, the road to the future is sometimes shrouded in mist. The super-resolution optical microscopy roadmap of Journal of Physics D: Applied Physics addresses this need for clarity. It provides guidance to the outstanding questions through a collection of short review articles from experts in the field, giving a thorough discussion on the concepts underlying super-resolution optical microscopy, the potential of different approaches, the importance of label optimization (such as reversible photoswitchable proteins) and applications in which these methods will have a significant impact.

 

Title:
Polycrystalline anatase titanium dioxide microring resonators with negative thermo-optic coefficient
Authors:
Reshef, Orad; Shtyrkova, Katia; Moebius, Michael G.; Griesse-Nascimento, Sarah; Spector, Steven; Evans, Christopher C.; Ippen, Erich; Mazur, Eric
Publication:
Journal of the Optical Society of America B, vol. 32, issue 11, p. 2288
Publication Date:
11/2015
Origin:
CROSSREF
DOI:
10.1364/JOSAB.32.002288
Bibliographic Code:
2015JOSAB..32.2288R

Abstract

Not Available

 

Title:
On the ground state wave function of matrix theory
Authors:
Lin, Ying-Hsuan; Yin, Xi
Publication:
Journal of High Energy Physics, Volume 2015, article id. #27, 19 pp.
Publication Date:
11/2015
Origin:
SPRINGER
Keywords:
Supersymmetric gauge theory, Field Theories in Lower Dimensions, M(atrix) Theories, M-Theory
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP11(2015)027
Bibliographic Code:
2015JHEP...11..027L

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:
VLBI for Gravity Probe B: the guide star, IM Pegasi
Authors:
Bartel, N.; Bietenholz, M. F.; Lebach, D. E.; Ransom, R. R.; Ratner, M. I.; Shapiro, I. I.
Publication:
Classical and Quantum Gravity, Volume 32, Issue 22, article id. 224021 (2015). (CQGra Homepage)
Publication Date:
11/2015
Origin:
IOP
DOI:
10.1088/0264-9381/32/22/224021
Bibliographic Code:
2015CQGra..32v4021B

Abstract

We review the radio very long baseline interferometry (VLBI) observations of the guide star, IM Peg, and three compact extragalactic reference sources, made in support of the NASA/Stanford gyroscope relativity mission, Gravity Probe B (GP-B). The main goal of the observations was the determination of the proper motion of IM Peg relative to the distant Universe. VLBI observations made between 1997 and 2005 yield a proper motion of IM Peg of -20.83 ± 0.09 mas yr‑1 in α and -27.27 ± 0.09 mas yr‑1 in δ in a celestial reference frame of extragalactic radio galaxies and quasars virtually identical to the International Celestial Reference Frame 2 (ICRF2). They also yield a parallax for IM Peg of 10.37 ± 0.07 mas, corresponding to a distance of 96.4 ± 0.7 pc. The uncertainties are standard errors with statistical and estimated systematic contributions added in quadrature. These results met the pre-launch requirements of the GP-B mission to not discernibly degrade the estimates of the geodetic and frame-dragging effects.

 

Title:
The Gravity Probe B test of general relativity
Authors:
Everitt, C. W. F.; Muhlfelder, B.; DeBra, D. B.;... Shapiro, I. I.;... .; and 91 coauthors
Publication:
Classical and Quantum Gravity, Volume 32, Issue 22, article id. 224001 (2015). (CQGra Homepage)
Publication Date:
11/2015
Origin:
IOP
DOI:
10.1088/0264-9381/32/22/224001
Bibliographic Code:
2015CQGra..32v4001E

Abstract

The Gravity Probe B mission provided two new quantitative tests of Einstein’s theory of gravity, general relativity (GR), by cryogenic gyroscopes in Earth’s orbit. Data from four gyroscopes gave a geodetic drift-rate of -6601.8 ± 18.3 marc-s yr-1 and a frame-dragging of -37.2 ± 7.2 marc-s yr-1, to be compared with GR predictions of -6606.1 and -39.2 marc-s yr-1 (1 marc-s = 4.848 × 10-9 radians). The present paper introduces the science, engineering, data analysis, and heritage of Gravity Probe B, detailed in the accompanying 20 CQG papers.

 

Title:
Non-Kähler SYZ Mirror Symmetry
Authors:
Lau, Siu-Cheong; Tseng, Li-Sheng; Yau, Shing-Tung
Publication:
Communications in Mathematical Physics, Volume 340, Issue 1, pp.145-170
Publication Date:
11/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: Springer-Verlag Berlin Heidelberg
DOI:
10.1007/s00220-015-2454-1
Bibliographic Code:
2015CMaPh.340..145L

Abstract

We study SYZ mirror symmetry in the context of non-Kähler Calabi-Yau manifolds. In particular, we study the six-dimensional Type II supersymmetric SU(3) systems with Ramond-Ramond fluxes, and generalize them to higher dimensions. We show that Fourier-Mukai transform provides the mirror map between these Type IIA and Type IIB supersymmetric systems in the semi-flat setting. This is concretely exhibited by nilmanifolds.

 

Title:
Dynamical Cooper pairing in non-equilibrium electron-phonon systems
Authors:
Knap, Michael; Babadi, Mehrtash; Refael, Gil; Martin, Ivar; Demler, Eugene
Publication:
eprint arXiv:1511.07874
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Bibliographic Code:
2015arXiv151107874K

Abstract

Ultrafast laser pulses have been used to manipulate complex quantum materials and to induce dynamical phase transitions. One of the most striking examples is the transient enhancement of superconductivity in several classes of materials upon irradiating them with high intensity pulses of terahertz light. Motivated by these experiments we analyze the Cooper pairing instabilities in non-equilibrium electron-phonon systems. We demonstrate that the light induced non-equilibrium state of phonons results in the following phenomena: an increase in the time averaged superconducting coupling constant, its periodic modulation, and an increase in the electron scattering. While the first two enhance Cooper pairing, the third one suppresses it. We analyze the competition between these effects and show that in a broad range of parameters the dynamic enhancement of pair formation dominates over the increase in the scattering rate. This opens the possibility of transient light induced superconductivity at temperatures that are considerably higher than the equilibrium transition temperatures. Our results pave new pathways for engineering high-temperature light-induced superconducting states.

 

Title:
Infinite-Dimensional Fermionic Symmetry in Supersymmetric Gauge Theories
Authors:
Dumitrescu, Thomas T.; He, Temple; Mitra, Prahar; Strominger, Andrew
Publication:
eprint arXiv:1511.07429
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, High Energy Physics - Phenomenology
Comment:
39 pages
Bibliographic Code:
2015arXiv151107429D

Abstract

We establish the existence of an infinite-dimensional fermionic symmetry in four-dimensional supersymmetric gauge theories by analyzing semiclassical photino dynamics in abelian ${\cal N}=1$ theories with charged matter. The symmetry is parametrized by a spinor-valued function on an asymptotic $S^2$ at null infinity. It is not manifest at the level of the Lagrangian, but acts non-trivially on physical states, and its Ward identity is the soft photino theorem. The infinite-dimensional fermionic symmetry resides in the same ${\cal N}=1$ supermultiplet as the physically non-trivial large gauge symmetries associated with the soft photon theorem.

 

Title:
Nonthermal production of dark radiation and dark matter
Authors:
Reece, Matthew; Roxlo, Thomas
Publication:
eprint arXiv:1511.06768
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Bibliographic Code:
2015arXiv151106768R

Abstract

Dark matter may be coupled to dark radiation: light degrees of freedom that mediate forces between dark sector particles. Cosmological constraints favor dark radiation that is colder than Standard Model radiation. In models with fixed couplings between dark matter and the Standard Model, these constraints can be difficult to satisfy if thermal equilibrium is assumed in the early universe. We construct a model of asymmetric reheating of the visible and dark sectors from late decays of a long-lived particle (for instance, a modulus). We show, as a proof-of-principle, that such a model can populate a sufficiently cold dark sector while also generating baryon and dark matter asymmetries through the out of equilibrium decay. We frame much of our discussion in terms of the scenario of dissipative dark matter, as in the Double-Disk Dark Matter scenario. However, our results may also be of interest for other scenarios like the Twin Higgs model that are in danger of overproducing dark radiation due to nonnegligible dark-visible couplings.

 

Title:
Griffiths effects and slow dynamics in nearly many-body localized systems
Authors:
Gopalakrishnan, Sarang; Agarwal, Kartiek; Huse, David A.; Demler, Eugene; Knap, Michael
Publication:
eprint arXiv:1511.06389
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Statistical Mechanics
Comment:
11 pages, 2 figures
Bibliographic Code:
2015arXiv151106389G

Abstract

The low-frequency response of systems near a many-body localization transition can be dominated by rare regions that are locally critical or ``in the other phase''. It is known that, in one dimension, these rare regions can cause the d.c. conductivity and diffusion constant to vanish even inside the delocalized thermal phase. Here, we present a general analysis of such Griffiths effects in the thermal phase near the many-body localization transition: we consider both one-dimensional and higher-dimensional systems, subject to quenched randomness, and discuss both linear response (including the frequency- and wavevector-dependent conductivity) and more general dynamics. In all the regimes we consider, we identify observables that are dominated by rare-region effects. In some cases (one-dimensional systems and Floquet systems with no extensive conserved quantities), essentially all long-time local observables are dominated by rare-region effects; in others, generic observables are instead dominated by hydrodynamic long-time tails throughout the thermal phase, and one must look at specific probes, such as spin echo, to see Griffiths behavior.

 

Title:
Site-resolved imaging of a fermionic Mott insulator
Authors:
Greif, Daniel; Parsons, Maxwell F.; Mazurenko, Anton; Chiu, Christie S.; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus
Publication:
eprint arXiv:1511.06366
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases
Comment:
6+7 pages
Bibliographic Code:
2015arXiv151106366G

Abstract

The complexity of quantum many-body systems originates from the interplay of strong interactions, quantum statistics, and the large number of quantum-mechanical degrees of freedom. Probing these systems on a microscopic level with single-site resolution offers unique insight with unprecedented control. Here we report site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators using ultracold atoms in a square lattice. We observe large, defect-free 2D Mott insulators for strong repulsive interactions. For intermediate interactions we observe a coexistence of phases. From comparison to theory we find trap-averaged entropies per particle of $1.0\,k_{\mathrm{B}}$ and local entropies as low as $0.5\,k_{\mathrm{B}}$. This experiment is a vital step towards probing quantum-mechanical models in regimes inaccessible by modern theoretical methods.

 

Title:
On the construction of charged operators inside an eternal black hole
Authors:
Guica, Monica; Jafferis, Daniel L.
Publication:
eprint arXiv:1511.05627
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
44 pp
Bibliographic Code:
2015arXiv151105627G

Abstract

We revisit the holographic construction of (approximately) local bulk operators inside an eternal AdS black hole in terms of operators in the boundary CFTs. If the bulk operator carries charge, the construction must involve a qualitatively new object: a Wilson line that stretches between the two boundaries of the eternal black hole. This operator - more precisely, its zero mode - cannot be expressed in terms of the boundary currents and only exists in entangled states dual to two-sided geometries, which suggests that it is a state-dependent operator. We determine the action of the Wilson line on the relevant subspaces of the total Hilbert space, and show that it behaves as a local operator from the point of view of either CFT. For the case of three bulk dimensions, we give explicit expressions for the charged bulk field and the Wilson line. Furthermore, we show that when acting on the thermofield double state, the Wilson line may be extracted from a limit of certain standard CFT operator expressions. We also comment on the relationship between the Wilson line and previously discussed mirror operators in the eternal black hole.

 

Title:
F-theory and the Classification of Little Strings
Authors:
Bhardwaj, Lakshya; Del Zotto, Michele; Heckman, Jonathan J.; Morrison, David R.; Rudelius, Tom; Vafa, Cumrun
Publication:
eprint arXiv:1511.05565
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
76 pages, 7 figures
Bibliographic Code:
2015arXiv151105565B

Abstract

Little string theories (LSTs) are UV complete non-local 6D theories decoupled from gravity in which there is an intrinsic string scale. In this paper we present a systematic approach to the construction of supersymmetric LSTs via the geometric phases of F-theory. Our central result is that all LSTs with more than one tensor multiplet are obtained by a mild extension of 6D superconformal field theories (SCFTs) in which the theory is supplemented by an additional, non-dynamical tensor multiplet, analogous to adding an affine node to an ADE quiver, resulting in a negative semidefinite Dirac pairing. We also show that all 6D SCFTs naturally embed in an LST. Motivated by physical considerations, we show that in geometries where we can verify the presence of two elliptic fibrations, exchanging the roles of these fibrations amounts to T-duality in the 6D theory compactified on a circle.

 

Title:
Strong quantum scarring by local impurities
Authors:
Luukko, Perttu J. J.; Drury, Byron; Klales, Anna; Kaplan, Lev; Heller, Eric J.; Räsänen, Esa
Publication:
eprint arXiv:1511.04198
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
Quantum Physics
Comment:
Letter-length draft with Supplementary Material
Bibliographic Code:
2015arXiv151104198L

Abstract

We discover and characterize strong quantum scars, or eigenstates resembling classical periodic orbits, in two-dimensional quantum wells perturbed by local impurities. These scars are not explained by ordinary scar theory, which would require the existence of short, moderately unstable periodic orbits in the perturbed system. Instead, they are supported by classical resonances in the unperturbed system and the resulting quantum near-degeneracy. Even in the case of a large number of randomly scattered impurities, the scars prefer distinct orientations that extremize the overlap with the impurities. We demonstrate that these preferred orientations can be used for highly efficient transport of quantum wave packets across the perturbed potential landscape. Assisted by the scars, wave-packet recurrences are significantly stronger than in the unperturbed system. Together with the controllability of the preferred orientations, this property may be very useful for quantum transport applications.

 

Title:
N=4 Superconformal Bootstrap of the K3 CFT
Authors:
Lin, Ying-Hsuan; Shao, Shu-Heng; Simmons-Duffin, David; Wang, Yifan; Yin, Xi
Publication:
eprint arXiv:1511.04065
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
60 pages, 9 figures
Bibliographic Code:
2015arXiv151104065L

Abstract

We study two-dimensional (4,4) superconformal field theories of central charge c=6, corresponding to nonlinear sigma models on K3 surfaces, using the superconformal bootstrap. This is made possible through a surprising relation between the BPS N=4 superconformal blocks with c=6 and bosonic Virasoro conformal blocks with c=28, and an exact result on the moduli dependence of a certain integrated BPS 4-point function. Nontrivial bounds on the non-BPS spectrum in the K3 CFT are obtained as functions of the CFT moduli, that interpolate between the free orbifold points and singular CFT points. We observe directly from the CFT perspective the signature of a continuous spectrum above a gap at the singular moduli, and find numerically an upper bound on this gap that is saturated by the $A_1$ N=4 cigar CFT. We also derive an analytic upper bound on the first nonzero eigenvalue of the scalar Laplacian on K3 in the large volume regime, that depends on the K3 moduli data. As two byproducts, we find an exact equivalence between a class of BPS N=2 superconformal blocks and Virasoro conformal blocks in two dimensions, and an upper bound on the four-point functions of operators of sufficiently low scaling dimension in three and four dimensional CFTs.

 

Title:
Fractional Quantum Hall Effect and M-Theory
Authors:
Vafa, Cumrun
Publication:
eprint arXiv:1511.03372
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, High Energy Physics - Theory
Comment:
28 pages. Major clarifications and extensions, including the distinction between edge modes for the superconducting and sharp edge boundary conditions. Section 4.2 expanded and contains a self-contained summary of the proposal. Possibility of lifting the construction to 3+1 d and potential experimental realization of non-abelian Yang-Mills theory for topological insulators is pointed out
Bibliographic Code:
2015arXiv151103372V

Abstract

We propose a unifying model for FQHE which on the one hand connects it to recent developments in string theory and on the other hand leads to new predictions for the principal series of experimentally observed FQH systems with filling fraction $\nu ={n\over 2n\pm1}$ as well as those with $\nu ={m\over m+2}$. Our model relates these series to minimal unitary models of the Virasoro and superVirasoro algebra and is based on $SL(2, {\bf C})$ Chern-Simons theory in Euclidean space or $SL(2,{\bf R})\times SL(2,{\bf R})$ Chern-Simons theory in Minkowski space. This theory, which has also been proposed as a soluble model for 2+1 dimensional quantum gravity, and its N=1 supersymmetric cousin, provide effective descriptions of FQHE. The principal series corresponds to quantized levels for the two $SL(2,{\bf R})$'s such that the diagonal $SL(2,{\bf R})$ has level $ 1$. The model predicts, contrary to standard lore, that for principal series of FQH systems the quasiholes possess non-abelian statistics. For the multi-layer case we propose that complex ADE Chern-Simons theories provide effective descriptions, where the rank of the ADE is mapped to the number of layers. Six dimensional $(2,0)$ ADE theories on the Riemann surface $\Sigma$ provides a realization of FQH systems in M-theory. Moreover we propose that the q-deformed version of Chern-Simons theories are related to the anisotropic limit of FQH systems which splits the zeroes of the Laughlin wave function. Extensions of the model to 3+1 dimensions, which realize topological insulators with non-abelian topologically twisted Yang-Mills theory is pointed out.

 

Title:
Superconformal Index, BPS Monodromy and Chiral Algebras
Authors:
Cecotti, Sergio; Song, Jaewon; Vafa, Cumrun; Yan, Wenbin
Publication:
eprint arXiv:1511.01516
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
91+2 pages, 4 figures; v2 references added
Bibliographic Code:
2015arXiv151101516C

Abstract

We show that specializations of the 4d $\mathcal{N}=2$ superconformal index labeled by an integer $N$ is given by $\textrm{Tr}\,{\cal M}^N$ where ${\cal M}$ is the Kontsevich-Soibelman monodromy operator for BPS states on the Coulomb branch. We provide evidence that the states enumerated by these limits of the index lead to a family of 2d chiral algebras $\mathcal{A}_{N}$. This generalizes the recent results for the $N=-1$ case which corresponds to the Schur limit of the superconformal index. We show that this specialization of the index leads to the same integrand as that of the elliptic genus of compactification of the superconformal theory on $S^2\times T^2$ where we turn on $\frac{1}{2} N$ units of $U(1)_r$ flux on $S^2$.

 

Title:
Calabi-Yau modular forms in limit: Elliptic Fibrations
Authors:
Haghighat, Babak; Movasati, Hossein; Yau, Shing-Tung
Publication:
eprint arXiv:1511.01310
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
Mathematics - Algebraic Geometry, High Energy Physics - Theory
Comment:
24 pages
Bibliographic Code:
2015arXiv151101310H

Abstract

We study the limit of Calabi-Yau modular forms, and in particular, those resulting in classical modular forms. We then study two parameter families of elliptically fibred Calabi-Yau fourfolds and describe the modular forms arising from the degeneracy loci. In the case of elliptically fibred Calabi-Yau threefolds our approach gives a mathematical proof of many observations about modularity properties of topological string amplitudes starting with the work of Candelas, Font, Katz and Morrison. In the case of Calabi-Yau fourfolds we derive new identities not computed before.

 

Title:
SUSY Higgs Mass and Collider Signals with a Hidden Valley
Authors:
Nakai, Yuichiro; Reece, Matthew; Sato, Ryosuke
Publication:
eprint arXiv:1511.00691
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
29 pages, 8 figures
Bibliographic Code:
2015arXiv151100691N

Abstract

We propose a framework of supersymmetric extensions of the Standard Model that can ameliorate both the SUSY Higgs mass problem and the missing superpartner problem. New vectorlike matter fields couple to the Higgs and provide new loop contributions to its mass. New Yukawa couplings are sizable and large supersymmetry breaking is not needed to lift the Higgs mass. To avoid a Landau pole for the new Yukawa couplings, these fields are charged under a new gauge group, which confines and leads to a Hidden Valley-like phenomenology. The Hidden Valley sector is almost supersymmetric and ordinary sparticles decay to exotic new states which decay back to Standard Model particles and gravitinos with reduced missing energy. We construct a simplified model to simulate this scenario and find a viable parameter space of specific benchmark models which ameliorates both of the major phenomenological problems with supersymmetry.

 

Title:
Elliptic Virasoro Conformal Blocks
Authors:
Iqbal, Amer; Kozcaz, Can; Yau, Shing-Tung
Publication:
eprint arXiv:1511.00458
Publication Date:
11/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
35 pages
Bibliographic Code:
2015arXiv151100458I

Abstract

We study certain six dimensional theories arising on $(p,q)$ brane webs living on $\mathbb{R}\times S^1$. These brane webs are dual to toric elliptically fibered Calabi-Yau threefolds. The compactification of the space on which the brane web lives leads to a deformation of the partition functions equivalent to the elliptic deformation of the Ding-Iohara algebra. We compute the elliptic version Dotsenko-Fateev integrals and show that they reproduce the instanton counting of the six dimensional theory.


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