Scientific Series

Displaying 3517 - 3528 of 5164

The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos

Evan O'Connor California Institute of Technology
April 09, 2013

PIRSA:13040120
Cosmology
Classical and quantum circuit obfuscation with braids

Stephen Jordan National Institute of Standards and Technology
April 08, 2013

PIRSA:13040111
Quantum Foundations
2D to 4D Correspondence: Towers of Kinks versus Towers of Monopoles
April 05, 2013

PIRSA:13040031
Quantum Fields and Strings
Fundamental Physics with Optically Levitated Dielectric Objects

Asimina Arvanitaki Perimeter Institute for Theoretical Physics
April 04, 2013

PIRSA:13040114
Strong Gravity
Quantum key expansion based on entanglement-assisted quantum LDPC codes

Todd Brun University of Southern California
April 03, 2013

PIRSA:13040108
Quantum Information
Black holes as probes of fundamental physics

Vitor Cardoso Instituto Superior Tecnico - Departamento de Física
April 03, 2013

PIRSA:13040109
Particle Physics

Cosmology
Three-point functions: SFT, integrability, and perturbative calculations.
April 02, 2013

PIRSA:13040110
Quantum Fields and Strings
To Split or Not to Split

Asimina Arvanitaki Perimeter Institute for Theoretical Physics
April 02, 2013

PIRSA:13040115
Particle Physics
Shake, Rattle and Explode: Short GRBs and the Electromagnetic Counterparts of Gravitational Wave Sources

Edo Berger Harvard University
April 02, 2013

PIRSA:13040081
Cosmology

Strong Gravity
S=1 spin liquid with fermionic excitations

Maksym Serbyn Massachusetts Institute of Technology (MIT)
March 28, 2013

PIRSA:13030113
Condensed Matter
Canonical gravity using unconstrained null initial data

Michael Reisenberger Universidad de la Republica Uruguay
March 28, 2013

PIRSA:13030092
Strong Gravity
Quoins versus Coins

Terry Rudolph Imperial College London
March 27, 2013

PIRSA:13030000
Quantum Information

The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos

Evan O'Connor California Institute of Technology
April 09, 2013

PIRSA:13040120
Cosmology
The endgame of massive star evolution is the gravitational-induced collapse of the central inert iron core. The collapse of the core continues until the matter reaches nuclear densities where the strong force between nucleons becomes dominant and provides sufficient pressure to stabilize the newly formed protoneutron star. What ensues is a complex multi-physics problem involving strong gravity, multidimensional hydrodynamic instabilities, magnetic fields, multispecies neutrino radiation, and supranuclear density physics to name a few.

We expect that most massive stars end this final stage of stellar evolution with a successful core-collapse supernova explosion. However, we also know that some of these core collapse events must fail and form stellar mass black holes.In his talk I will touch on two of the most important questions in core-collapse supernovae theory. I will briefly talk about what conditions are favourable for failed core-collapse supernovae (i.e. black hole formation). Conversely, I will discuss recent results from full three-dimensional, general-relativistic simulations of core-collapse and the implications for our understanding of the core-collapse supernova mechanism. If time permits, I'll discuss how neutrinos from the next galactic core-collapse supernova can help constrain properties of massive stars.
Classical and quantum circuit obfuscation with braids

Stephen Jordan National Institute of Standards and Technology
April 08, 2013

PIRSA:13040111
Quantum Foundations
A circuit obfuscator is an algorithm that translates logic circuits into functionally-equivalent similarly-sized logic circuits that are hard to understand. While ad hoc obfuscators have been implemented, theoretical progress has mainly been limited to no-go results. In this work, we propose a new notion of circuit obfuscation, which we call partial indistinguishability. We then prove that, in contrast to previous definitions of obfuscation, partial indistinguishability obfuscation can be achieved by a polynomial-time algorithm. Specifically, our algorithm re-compiles the given circuit using a gate that satisfies the relations of the braid group, and then reduces to a braid normal form. Variants of our obfuscation algorithm can be applied to both classical and quantum circuits.
2D to 4D Correspondence: Towers of Kinks versus Towers of Monopoles
April 05, 2013

PIRSA:13040031
Quantum Fields and Strings
Two-dimensional models provide for a very attractive playground being a theory imitating some of the main features of QCD. Those include the asymptotic freedom, mass gap, confinement, chiral symmetry breaking and others. Furthermore, there is a correspondence between the spectra of four-dimensional SQCD and N=(2,2) CP(N-1) sigma model which was discovered more than a decade ago. This correspondence was explained later when it was found that SQCD supports non-Abelian strings with confined monopoles. The kinks of the two-dimensional theory are the monopoles attached to the strings. Thus, analysis of two-dimensional sigma models gives a deeper insight into the four-dimensional SQCD, in particular, into its strong dynamics.

We study the BPS spectrum of the N=(2,2) CP(N-1) model with the Z_N-symmetric twisted mass terms. We focus on analysis of the "extra'' towers of states found previously and compare them to the states that can be identified in the quasiclassical domain. Exact analysis of the strong-coupling states shows that not all of them survive when passing to the weak-coupling domain. Some of the states decay on the curves of the marginal stability (CMS). Thus, most of the strong coupling states do not exist at weak coupling and cannot be classified quasiclassically. This result lifts to four dimensions. In terms of the four-dimensional theory, the "extra" states are the strong coupling dyons, while the quasiclassical bound states are the bound states of dyons and quarks.
Fundamental Physics with Optically Levitated Dielectric Objects

Asimina Arvanitaki Perimeter Institute for Theoretical Physics
April 04, 2013

PIRSA:13040114
Strong Gravity
In the past few years, optical cooling and manipulating of macroscopic objects, such as micro-mirrors and cantilevers has developed into an active field of research. In mechanical systems, the oscillator is attached to its suspension, a thermal contact that limits the motion isolation. On the other hand, when these small objects are levitated using the radiation pressure force of lasers, the excellent thermal isolation even at room temperatures helps produce very sensitive force detectors, and eventually quantum transducers for quantum computation purposes. These new techniques may have a variety of applications for fundamental physics such as short distance tests of gravity and gravitational wave detection at high frequencies. In addition, there are several proposals suggesting that optically levitated dielectrics can be cooled to the ground state of the center of mass motion, opening the exciting possibility of creating macroscopic matter-wave interferometers.
Quantum key expansion based on entanglement-assisted quantum LDPC codes

Todd Brun University of Southern California
April 03, 2013

PIRSA:13040108
Quantum Information
Quantum key distribution protocols can be based on quantum error correcting codes, where the structure of the code determines the post processing protocol applied to a raw key produced by BB84 or a similar scheme. Luo and Devetak showed that basing a similar protocol on entanglement-assisted quantum error-correcting codes (EAQECCs) leads to quantum key expansion (QKE) protocols, where some amount of previously shared secret key is used as a seed in the post-processing stage to produce a larger secret key. One of the promising aspects of EAQECCs is that they can be constructed from classical linear codes that don't satisfy the dual-containing property, which among other things allows the use of low density parity-check (LDPC) codes with girth greater than 4, for which the iterative decoding algorithm has better performance. We looked into QKE based on a family of EAQECCs generated by classical finite geometry (FG) LDPC codes. Very efficient iterative decoders exist for these codes, and they were shown by Hsieh, Yen and Hau to produce quantum LDPC codes that require very little entanglement. We modify the original QKE protocol to detect bad code blocks without the consumption of secret key when the protocol fails. This allows us to greatly reduce the bit error rate of the key, at the cost of a minor reduction in the net key production rate, but without increasing the consumption rate of pre-shared key. Numerical simulations for the family of FG LDPC codes show that this improved QKE protocol has a good net key production rate even at relatively high error rates, for appropriate code choices.
Black holes as probes of fundamental physics

Vitor Cardoso Instituto Superior Tecnico - Departamento de Física
April 03, 2013

PIRSA:13040109
Particle Physics

Cosmology
Black holes are the elementary particles of gravity, the final state of sufficiently massive stars and of energetic collisions. With a forty-year long history, black hole physics is a fully-blossomed field which promises to embrace several branches of theoretical physics. Here I review the main developments in highly dynamical black holes with an emphasis on high energy black hole collisions and probes of particle physics via superradiance.
Three-point functions: SFT, integrability, and perturbative calculations.
April 02, 2013

PIRSA:13040110
Quantum Fields and Strings
I discuss several recent efforts in relating string field theory calculations of BMN BMN BMN and BMN BMN BPS correlation functions to direct perturbative calculations and integrability-assisted methods. I review the next-to-leading order agreement between strings and perturbation theory in the SO(6) sector, a conjectured extension of the integrability techniques by Escobedo, Gromov, Sever, Vieira from the SU(2) to the full SO(6) sector and agreement with SFT and PT in it at the leading order; finally, I discuss the issue of equating exactly extremal and non-extremal correlators at NLO in the integrability-assisted calculation.
To Split or Not to Split

Asimina Arvanitaki Perimeter Institute for Theoretical Physics
April 02, 2013

PIRSA:13040115
Particle Physics
Physics is at a crossroad that leads either to Naturalness or the Multiverse. While the confirmation of gauge coupling unification in the early 90s gave a tremendous boost to naturalness and to low energy SUSY, the lack of evidence for new physics beyond the standard model at the LHC points to a paucity of new particles near the weak scale. This suggests that the weak scale is tuned and that supersymmetry, if present at all, is realized at higher energies. This points to Split SUSY, a framework motivated by the String Landscape. Fine-tuning electroweak symmetry breaking and the renormalization group evolution of the scalar masses constrains Split model building and I review the expectations at the LHC for the different possible Split SUSY particle spectra.
Shake, Rattle and Explode: Short GRBs and the Electromagnetic Counterparts of Gravitational Wave Sources

Edo Berger Harvard University
April 02, 2013

PIRSA:13040081
Cosmology

Strong Gravity
The bimodality of gamma-ray burst (GRB) durations points to distinct progenitor classes for the long- and short-duration GRBs. While the progenitors of long-duration GRBs are now known to be massive stars, the progenitors of short-duration GRBs remain unidentified. In this talk I will discuss the discovery of short GRB afterglow and their host galaxies, detailed studies of their environments from parsec to galactic scales, and studies of their energetics and beaming. Taken together, these observations point to the coalescence of NS-NS/NS-BH binaries as the most likely progenitors. With the upcoming Advanced LIGO/VIRGO gravitational wave detectors it is therefore possible that short GRBs will be the first detected sources, and I will discuss various approaches to making this connection between gravitational wave and electromagnetic sources.
S=1 spin liquid with fermionic excitations

Maksym Serbyn Massachusetts Institute of Technology (MIT)
March 28, 2013

PIRSA:13030113
Condensed Matter
In the first part of my talk I describe a search for possible quantum spin liquid ground states for spin S=1 Heisenberg models on the triangular lattice which was motivated by recent experiments on Ba3NiSb2O9. We use representation of spin-1 via three flavors of fermionic spinon operators. The ground state where one gapless flavor of spinons with a Fermi surface coexists with d+id topological pairing of the two other flavors can explain available experimental data. Despite the existence of a Fermi surface, this spin liquid state has fully gapped bulk spin excitations. This results in a linear in-temperature specific heat and constant in-plane spin susceptibility, with an unusually high Wilson ratio. Using variational Monte Carlo technique, we show that proposed spin liquid ground state is realized in an SU(3)-invariant model with sufficiently strong ring-exchange terms. In the second part, I consider the physics of the magnetic s=1/2 impurity embedded in a S=1 spin liquid, where all three flavors of spinons have a Fermi surface. The interplay between non-Fermi-liquid behavior induced by a U(1) gauge field coupled to fermions, and a non-Fermi-liquid fixed point in the overscreened Kondo problem is studied using double expansion. The gauge field changes the physical properties of the system at the overscreened Kondo fixed point. Thus, spin-half impurity in such spin liquid can be used to probe the presence of fermionic spinons coupled to the gauge field. References: arXiv:1108.3070, arXiv:1208.3231 and arXiv:1212.5179
Canonical gravity using unconstrained null initial data

Michael Reisenberger Universidad de la Republica Uruguay
March 28, 2013

PIRSA:13030092
Strong Gravity
Quoins versus Coins

Terry Rudolph Imperial College London
March 27, 2013

PIRSA:13030000
Quantum Information
Human monkeys are used to thinking about the problem of choosing from a set of objects according to some desired, biased, probability distribution. Just think about how you chose your partner(s). Even when it is easy for you to do such a sampling, it can be difficult to do a quantum sampling (Q-Sampling) of the same distribution. By Q-Sampling I mean the creation of a coherent superposition of states of such objects whose amplitudes are the (square roots of) of the specified distribution. In this talk I will discuss what we do know about this problem, why it is interesting, and will discuss how it can let us achieve tasks with quantum information that are provably impossible classically.

Title	Speaker(s)	Date	Talk Type	Info link
The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos	Evan O'Connor	2013-04-09	Scientific Series	View details
Classical and quantum circuit obfuscation with braids	Stephen Jordan	2013-04-08	Scientific Series	View details
2D to 4D Correspondence: Towers of Kinks versus Towers of Monopoles		2013-04-05	Scientific Series	View details
Fundamental Physics with Optically Levitated Dielectric Objects	Asimina Arvanitaki	2013-04-04	Scientific Series	View details
Quantum key expansion based on entanglement-assisted quantum LDPC codes	Todd Brun	2013-04-03	Scientific Series	View details
Black holes as probes of fundamental physics	Vitor Cardoso	2013-04-03	Scientific Series	View details
Three-point functions: SFT, integrability, and perturbative calculations.		2013-04-02	Scientific Series	View details
To Split or Not to Split	Asimina Arvanitaki	2013-04-02	Scientific Series	View details
Shake, Rattle and Explode: Short GRBs and the Electromagnetic Counterparts of Gravitational Wave Sources	Edo Berger	2013-04-02	Scientific Series	View details
S=1 spin liquid with fermionic excitations	Maksym Serbyn	2013-03-28	Scientific Series	View details
Canonical gravity using unconstrained null initial data	Michael Reisenberger	2013-03-28	Scientific Series	View details
Quoins versus Coins	Terry Rudolph	2013-03-27	Scientific Series	View details

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