# Events

#### Condensed Matter Seminar, Carlos Sa De Melo, Georgia Tech,"Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless transition . . . .

##### Jan 28, 2015 · 2:00 p.m.– 3:30 p.m. · PCTS Seminar Room

We investigate the Berezinskii-Kosterlitz-Thouless (BKT) transition in a two-dimensional (2D) Fermi gas with spin-orbit coupling (SOC), as a function of the two-body binding energy and a perpendicular Zeeman field [1]. By including a generic form of the SOC, as a function of Rashba and Dresselhaus terms, we study the evolution between the experimentally relevant equal Rashba-Dresselhaus (ERD) case and the Rashba-only (RO) case. We show that in the ERD case, at fixed non-zero Zeeman field, the BKT transition temperature TBKT is increased by the effect of the SOC for all values of the binding energy. We also find a significant increase in the value of the Clogston limit compared to the case without SOC. Furthermore, we demonstrate that the superfluid density tensor becomes anisotropic (except in the RO case), leading to an anisotropic phase-fluctuation action that describes elliptic vortices and anti-vortices, which become circular in the RO limit. This deformation constitutes an important experimental signature for superfluidity in a 2D Fermi gas with ERD SOC. Finally, we show that the anisotropic sound velocity exhibit anomalies at low temperatures in the vicinity of quantum phase transitions between topologically distinct uniform superfluid phases.

[1] “Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless transition and the vortex-antivortex structure in two-dimensional Fermi gases”, Jeroen P. A. Devreese, Jacques Tempere, and Carlos A. R. Sá de Melo, Phys. Rev. Lett.113, 165304 (2014).

#### Condensed Matter Seminar, Andrey Chubukov, U of Minn, "Charge order in the cuprates"

##### Feb 2, 2015 · 1:15 p.m.– 2:15 p.m. · PCTS Seminar Room

I analyze charge order in hole-doped cuprates. I argue that magnetically-mediated interaction, which is known to give rise to d-wave superconductivity, also gives rise to charge-density-wave instabilities with momenta Q_x =(Q,0) and Q_y =(0,Q), as seen in the experiments. I show that the emerging charge order with Q_x/Q_y is of stripe type and that a stripe CDW order parameter by itself has two components: one is incommensurate density variation, another is incommensurate current. Both components are non-zero in the CDW-ordered state, with the relative phase +- \pi/2. Such an order breaks time reversal and mirror symmetries and give rise to a non-zero Kerr effect. I further show that, before a true incommensurate CDW order sets in, the system develops a pre-emptive composite order which breaks lattice rotational symmetry and time-reversal symmetry but preserves a translational U(1) symmetry. I discuss the interplay between our CDW order and pair density-wave order (superconducting order with a finite total momentum of a pair) and present the phase diagram of underdoped cuprates.

#### Special Seminar -Fingers, toes and tongues: the anatomy of interfacial instabilities in viscous fluids - Irmgard Bischofberger, University of Chicago

##### Feb 2, 2015 · 2:30 p.m.– 3:30 p.m. · Jadwin A06

The invasion of one fluid into another of higher viscosity is unstable and produces complex patterns in a quasi-two dimensional geometry. This viscous-fingering instability,a bedrock of our understanding of pattern formation, has been characterized by a mostunstable wavelength that sets the characteristic width of the fingers. We have shown that a second, previously overlooked, parameter governs the length of the fingers and characterizes the dominant global features of the patterns.

Because interfacial tension suppresses short-wavelength fluctuations, its elimination would suggest an instability producing highly ramified singular structures. Our experimental investigations using miscible fluids show the opposite behavior – the

interface becomes more stable even as the stabilizing effect of interfacial tension is removed. This is accompanied by slender structures, tongues, that form in the narrow thickness of the fluid. Among the rich variety of global patterns that emerge is a regime

of blunt structures, “toes”, that exhibit the unusual features characteristic of proportionate growth. This type of pattern formation, while quite common in mammalian biology, was hitherto unknown in physical systems.

#### High Energy Theory Seminar IAS-Sean Hartnoll,Stanford U-Holographically Inspired Thoughts on High Temperature Superconductors and other Bad Metals

##### Feb 3, 2015 · 11:00 a.m.–12:00 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study

SPECIAL DATE

Bad metals are a class of materials whose transport properties cannot be understood within a weakly interacting quasiparticle description.

Away from weak interactions, the natural objects to characterize are the conserved charge and heat current operators. This talk concerns

two aspects of these operators. Firstly, many bad metals exhibit unexpectedly similar transport behavior. We suggest that this could be

explained by a certain universal bound on charge and heat diffusivities. Secondly, the cuprate high temperature superconductors are especially

important examples of bad metals. Transport in the most puzzling part of the cuprate phase diagram is characterized by multiple scaling laws.

I will show that at least five of these scaling laws can be understood from only two nontrivial critical exponents. One of these is an anomalous

dimension for the charge density operator.

#### High Energy Theory Seminar IAS - Shamit Kachru, Stanford U-Comments on Elliptic Genera and 3d Gravity

##### Feb 3, 2015 · 1:30 p.m.– 2:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study

SPECIAL DATE

I discuss simple constraints on the elliptic genera of 2d superconformal field theories which admit weakly curved gravity duals.

#### Math Physics Seminar, Alessandro Giuliani, U. of Rome 3, "Height Fluctuations in Interacting Dimers"

##### Feb 3, 2015 · 4:30 p.m.– 6:00 p.m. · Jadwin 343

Perfect matchings of Z^2 (also known as non-interacting dimers on the square lattice) are an exactly solvable 2D statistical mechanics model. It is known that the associated height function behaves at large distances like a massless gaussian field, with the variance of height gradients growing logarithmically with the distance. As soon as dimers mutually interact, via e.g. a local energy function favoring the alignment among neighboring dimers, the model is not solvable anymore and the dimer-dimer correlation functions decay polynomially at infinity with a non-universal (interaction-dependent) critical exponent. We prove that, nevertheless, the height fluctuations remain gaussian even in the presence of interactions, in the sense that all their moments converge to the gaussian ones at large distances. The proof is based on a combination of multiscale methods with the path-independence properties of the height function. Joint work with V. Mastropietro and F. Toninelli.

#### Special Seminar - Magnetic resonance with Single-Nuclear-Spin Sensitivity - Alex Sushkov, Harvard University

##### Feb 4, 2015 · 2:00 p.m.– 3:00 p.m. · Jadwin A06

Our method of nanoscale magnetic sensing and imaging makes use of nitrogen-vacancy (NV) color centers a few nanometers below the surface of a diamond crystal. Using individual NV centers, we perform NMR experiments on single protein molecules, labeled with carbon-13 and deuterium isotopes. In order to achieve single nuclear-spin sensitivity, we use isolated electronic-spin quantum bits (qubits), that are present of the diamond surface, as magnetic resonance "reporters". Their quantum state is coherently manipulated and measured optically via a proximal NV center. This system is used for sensing, coherent coupling, and imaging of individual proton spins on the diamond surface with angstrom resolution. Our approach may enable magnetic structural imaging of individual complex molecules, and realizes a new platform for probing novel materials, and manipulation of interacting spin systems.

#### Particle Physics Seminar, Jack Kearney,FNAL "Explaining the "Inexplicable:" Achieving dark sector mass relations via renormalization group focusing."

##### Feb 6, 2015 · 4:00 p.m.– 5:00 p.m. · Jadwin 111

As constraints on dark matter from direct detection, indirect detection and collider experiments become more stringent, many models of electroweak-scale dark matter must now exhibit very specific mass relations in the dark sector to remain viable. For instance, the dark matter may be close in mass to another state, permitting coannihilation with or phase-space suppressed annihilation to the other state. Alternatively, the dark matter mass may be approximately half that of a resonance. We discuss the idea that such mass relations could arise due to IR-attractive ratios in renormalization group equations. Achieving a particular ratio requires specific dark matter gauge charges or interactions, leading to predictions about the dark matter properties. Furthermore, additional states with masses comparable to the dark matter mass may be necessary, potentially giving rise to novel phenomenology. We explore this idea in the context of dark matter charged under a new gauged U(1) that kinetically mixes with the Standard Model hypercharge.

#### Condensed Matter Seminar, Dmitry Abanin, Perimeter Institute, "TBA"

##### Feb 9, 2015 · 1:15 p.m.– 2:30 p.m. · PCTS Seminar Room

TBA

#### High Energy Theory Seminar- Jared Kaplan, Johns Hopkins University - TBA

##### Feb 9, 2015 · 2:30 p.m.– 3:30 p.m. · PCTS Seminar Room

#### Special Seminar - Joanna Dunkley

##### Feb 9, 2015 · 3:30 p.m.– 4:30 p.m. · Jadwin A06

#### Math Physics Seminar, Michael Kiessling, Rutgers, "A novel quantum-mechanical interpretation of the Dirac equation"

##### Feb 10, 2015 · 4:30 p.m.– 5:30 p.m. · Jadwin 343

A novel interpretation is given of Dirac's ``wave equation for the relativistic electron'' as a quantum-mechanical one-particle equation in which electron and positron are merely the two different ``topological spin'' states of a single more fundamental particle, not distinct particles in their own right. The new interpretation is backed up by the existence of such binary particle structures in general relativity, in particular the curvature singularity of the maximal analytically extended,topologically non-trivial, electromagnetic Kerr--Newman spacetime in the zero-gravity limit. The pertinent general-relativistic zero-gravity Hydrogen problem is studied in the usual Born--Oppenheimer approximation. Its spectral results suggest that the zero-$G$ Kerr--Newman magnetic moment be identified with the so-called ``anomalous magnetic moment of the physical electron,'' not with the Bohr magneton, so that the ring radius is only a tiny fraction of the electron's Compton wave length. This is joint work with A. Shadi Tahvildar-Zadeh.

#### Hamilton Colloquium Series - Zheng-Tian Lu, ANL, U. Chicago, "Atom Trap, Krypton-81, and Global Groundwater"

##### Feb 12, 2015 · 4:30 p.m.– 6:00 p.m. · Jadwin A10

The long-lived noble-gas isotope 81Kr is the ideal tracer for water and ice with ages of 10^5 – 10^6 years, a range beyond the reach of 14C. 81Kr-dating, a concept pursued over the past five decades by numerous laboratories employing a variety of techniques, is finally available to the earth science community at large. This is made possible by the development of the Atom Trap Trace Analysis (ATTA) method, in which individual atoms of the desired isotope are captured and detected. ATTA possesses superior selectivity, and is thus far used to analyze the environmental radioactive isotopes 81Kr, 85Kr, and 39Ar, These three isotopes have extremely low isotopic abundances in the range of 10^-16 to 10^-11, and cover a wide range of ages and applications. In collaboration with earth scientists, we are dating groundwater and mapping its flow in major aquifers around the world. We have also demonstrated for the first time 81Kr-dating of old ice.

This work is supported by DOE, Office of Nuclear Physics, under contract DE-AC02-06CH11357. Development of the ATTA-3 instrument was supported in part by NSF under grant EAR-0651161.

#### Particle Physics Seminar, Matthew Low, U of Chicago, "TBA"

##### Feb 13, 2015 · 4:00 p.m.– 5:00 p.m. · Jadwin 111

TBA

#### High Energy Theory Seminar - Xi Yin, Harvard University - "On the UV completion of 6d SYM"

##### Feb 16, 2015 · 2:30 p.m.– 3:30 p.m. · PCTS Seminar Room

I will discuss an interpolation on the Coulomb branch of (1,1) little string theory, from perturbative 6d SYM to double scaled little string theory, by analyzing scattering amplitudes and the related derivative expansion of the Coulomb branch effective action.

#### Hamilton Colloquium Series - Charles Kane, University of Pennsylvania, "Topological Boundary Modes from Quantum Electronics to Classical Mechanics"

##### Feb 19, 2015 · 4:30 p.m.– 6:00 p.m. · Jadwin A10

Over the past several years, our understanding of topological electronic phases of matter has advanced dramatically. A paradigm that has emerged is that insulating electronic states with an energy gap fall into distinct topological classes. Interfaces between different topological phases exhibit gapless conducting states that are protected topologically and are impossible to get rid of. In this talk we will discuss the application of this idea to the quantum Hall effect, topological insulators, topological superconductors and the quest for Majorana fermions in condensed matter. We will then show that similar ideas arise in a completely different class of problems. Isostatic lattices are arrays of masses and springs that are at the verge of mechanical instability. They play an important role in our understanding of granular matter, glasses and other 'soft' systems. Depending on their geometry, they can exhibit zero-frequency 'floppy' modes localized on their boundaries that are insensitive to local perturbations. The mathematical relation between this classical system and quantum electronic systems reveals an unexpected connection between theories of hard and soft matter.

#### Particle Physics Seminar, Yue Zhao, Stanford U."The Solution of (Little) Hierarchy Problem in AdS3/CFT2 Avatar"

##### Feb 20, 2015 · 4:00 p.m.– 5:00 p.m. · Jadwin 111

There is an avatar of the (little) hierarchy problem of the MSSM in 3-dimensional supersymmetry. We propose a solution to this problem in AdS3. The generalization to AdS5 is possible which may have implication to Randall-Sundrum model. In the AdS3 toy model, the bulk theory is a supergravity theory in which U(1) × U(1) R-symmetry is gauged by Chern-Simons fields. The bulk theory is deformed by a boundary term quadratic in the gauge fields. It breaks SUSY completely and sources an exactly marginal operator in the dual CFT. SUSY breaking is communicated by gauge interactions to bulk scalar fields and their spinor superpartners. Since the R-charges of scalar and spinor differ, this generates a SUSY breaking shift of their masses. The Ward identity facilitates the calculation of these mass shifts to any desired order in the strength of the deformation. Moduli fields are massless R-neutral bulk scalars with vanishing potential in the undeformed theory. These properties are maintained to all orders in the deformation despite the fact that moduli couple in the bulk to loops of R-charged fields.

#### Condensed Matter Seminar, N. Peter Armitage, Johns Hopkins,"Shining (low frequency) light on quantum magnets: Ising spin chains, quantum spin ice, an

##### Feb 23, 2015 · 1:15 p.m.– 2:30 p.m. · PCTS Seminar Room

Although typically we regard optical spectroscopies as probes of electronic degrees of freedom in materials, light's time-varying magnetic field allows one to couple to magnetic degrees of freedom. This talk will review recent advances in the area of time-domain THz spectroscopy and its application to “quantum" magnets. Our high signal to noise, routinely excellent energy resolution, and unique ability to measure complex response functions gives unique insight into the magnetic response of quantum materials and gives several distinct advantages in these matters over neutron scattering. I will give examples of the use of the technique on quantum magnet systems as diverse as 1D Ising spin chains, quantum spin ices, and spin-orbital liquids.

#### Math Physics Seminar, Subhro Ghosh, Princeton, TBA

##### Feb 24, 2015 · 4:30 p.m.– 5:30 p.m. · Jadwin 343

TBA

#### Special Seminar - "Hostile and Benevolent Sexism: A Discussion for Women and Men in STEM." - Susan Fiske - Princeton University

##### Feb 25, 2015 · 12:00 p.m.– 1:30 p.m. · Joseph Henry Room

#### High Energy Theory Seminar - Victor Mikhaylov, Princeton University - TBA

##### Feb 27, 2015 · 1:45 p.m.– 3:00 p.m. · PCTS Seminar Room

#### Particle Physics Seminar, Matthew Baumgart, Carnegie Mellon, "TBA"

##### Feb 27, 2015 · 4:00 p.m.– 5:00 p.m. · Jadwin 111

TBA

#### High Energy Theory Seminar IAS - Leonardo Rastelli, SUNY Stonybrook - TBA

##### Mar 2, 2015 · 2:30 p.m.– 3:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study

#### High Energy Theory Seminar - Marco Bochicchio, Sapienza University of Rome - An asymptotic solution of large-N QCD, and of large-N n=1 SUSY YM

##### Mar 9, 2015 · 2:30 p.m.– 3:30 p.m. · TBD

We find an asymptotic solution for two-, three- and, to some extent, multi-point correlators of local gauge-invariant operators, in a lower-spin sector

of massless large-N QCD (and of n=1 SUSY YM), in terms of glueball and meson propagators, in such a way that the solution is asymptotic in the

ultraviolet to renormalization-group improved perturbation theory, by means of a new purely field-theoretical technique that we call the asymptotically-free bootstrap,

based on a recently-proved asymptotic structure theorem for two-point correlators.

The asymptotically-free bootstrap provides as well asymptotic S-matrix amplitudes in terms of glueball and meson propagators. Remarkably, the asymptotic S-matrix depends

only on the unknown particle spectrum, but not on the anomalous dimensions, as a consequence of the LSZ reduction formulae.

Very many physics consequences follow, both practically and theoretically. In fact, the asymptotic solution sets the strongest constraints on any actual

solution of large-N QCD (and of n=1 SUSY YM), and in particular on any string solution.

#### High Energy Theory Seminar IAS - Jacques Distler, University of Texas - TBA

##### Mar 16, 2015 · 2:30 p.m.– 3:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study

#### High Energy Theory Seminar - Andreas Stergiou, Yale University - "Trace anomaly on the conformal manifold"

##### Mar 23, 2015 · 2:30 p.m.– 3:30 p.m. · PCTS Seminar Room

Conformal field theories (CFTs) defined at fixed points of the

renormalization group flow can be lifted to curved space where they develop

the well-known trace anomaly. In this talk we will consider the trace

anomaly of CFTs with exactly marginal operators. The couplings that source

the marginal operators are promoted to spacetime-dependent functions, and

new terms, proportional to derivatives of the couplings, appear in the trace

anomaly. We will analyze these contributions in four and six spacetime

dimensions, and illustrate their relevance to the a-theorem and the

relation between scale and conformal invariance. The six-dimensional case

displays novel features not seen in lower dimensions.

#### High Energy Theory Seminar - Matthew Buican, Rutgers University - TBA

##### Mar 27, 2015 · 1:45 p.m.– 3:00 p.m. · PCTS Seminar Room

#### High Energy Theory Seminar IAS - Bobby Acharya, ICTP Trieste & King's College London - TBA

##### Mar 30, 2015 · 2:30 p.m.– 3:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study

#### Hamilton Colloquium Series - Cindy Regal, University of Colorado, "Interferometry in a strong light"

##### Apr 2, 2015 · 4:30 p.m.– 6:00 p.m. · Jadwin A10

Abstract: TBA

#### Condensed Matter Seminar, Allan MacDonald, UT, Austin, TBA

##### Apr 6, 2015 · 1:05 p.m.– 2:30 p.m. · PCTS Seminar Room

TBA

#### Math Physics Seminar, Wendelin Werner, ETS, Zurich, TBA

##### Apr 7, 2015 · 4:30 p.m.– 5:30 p.m. · Jadwin 343

TBA

#### Particle Physics Seminar, Illias Cholis, FNAL, "WIMP ante portas? The Fermi galactic center excess."

##### Apr 10, 2015 · 4:00 p.m.– 5:00 p.m. · Jadwin 111

The possible gamma-ray excess in the inner Galaxy and the Galactic center suggested by Fermi-LAT observations has triggered great interest in the community. Among its various interpretations have been WIMP dark matter annihilations, gamma-ray emission from a population of millisecond pulsars, or emission from cosmic rays injected in a sequence of burst-like events or continuously at the GC. Given that the galactic diffuse emission is the dominant (by an order of magnitude or more) at any direction greater than 2 degrees from the GC understanding the background systematics has been a vital missing piece in the discussion. I will present the first comprehensive study of model systematics coming from the Galactic diffuse emission in the inner part of our Galaxy and their impact on the inferred properties of the excess emission at Galactic latitudes between 2 and 20 degrees and energies 300 MeV to 500 GeV. I will show both theoretical and empirical model systematics, which are deduced from a large range of Galactic diffuse emission models and a principal component analysis of residuals in numerous test regions along the Galactic plane. The hypothesis of an extended spherical excess emission with a uniform energy spectrum is compatible with the Fermi-LAT data in the region of interest at 95% CL. Assuming that this excess is the extended counterpart of the one seen in the inner few degrees of the Galaxy, a lower limit of 10 degrees (95% CL) can be derived on its extension away from the GC. In light of the large correlated uncertainties that affect the subtraction of the Galactic diffuse emission in the relevant regions, the energy spectrum of the excess is equally compatible with both a simple broken power-law of break energy 2.1 $\pm$ 0.2 and with spectra predicted by the self-annihilation of dark matter, implying in the case of $\bar{b}b$ final states a dark matter mass of 49$^{+6.4}_{-5.4}$ GeV.

#### Annual Physics Recital

##### Apr 18, 2015 · 4:30 p.m.– 6:00 p.m. · Taplin Auditorium

#### Special Event - Physics Recital

##### Apr 18, 2015 · 6:00 p.m.– 8:00 p.m. · Taplin Auditorium

#### Condensed Matter Seminar, Joel Moore, UC, Berkeley, TBA

##### Apr 20, 2015 · 1:15 p.m.– 2:30 p.m. · PCTS Seminar Room

TBA

#### High Energy Theory Seminar- Itzhak Bars, University of Southern CA - TBA

##### Apr 20, 2015 · 2:30 p.m.– 3:30 p.m. · TBD

#### High Energy Theory Seminar - Filippo Passerini, Princeton University and Ecole Normale Supérieure - TBA

##### Apr 24, 2015 · 1:45 p.m.– 3:00 p.m. · TBD

#### High Energy Theory Seminar IAS - Neal Weiner, New York University - TBA

##### Apr 27, 2015 · 2:30 p.m.– 3:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study

#### 40th annual Donald Hamilton Lecture: Deborah Jin, University of Colorado; "Fun with Ultracold Atoms"

##### Apr 30, 2015 · 8:00 p.m.– 9:30 p.m. · McDonnell A02

Experiments with ultracold gases are among the coldest experiments in the world. I will discuss experiments where we are exploring quantum behavior in a gas of atoms cooled to temperatures near absolute zero. The talk will touch upon topics such as temperature, quantum mechanics, and superconductivity.

#### Condensed Matter Seminar, Inna Vishnik, MIT, ""Ultrafast dynamics in correlated electron systems"

##### May 4, 2015 · 1:15 p.m.– 2:30 p.m. · PCTS Seminar Room

TBA