2,412 research outputs found
On 2-group global symmetries and their anomalies
In general quantum field theories (QFTs), ordinary (0-form) global symmetries and 1-form symmetries can combine into 2-group global symmetries. We describe this phenomenon in detail using the language of symmetry defects. We exhibit a simple procedure to determine the (possible) 2-group global symmetry of a given QFT, and provide a classification of the related \u2019t Hooft anomalies (for symmetries not acting on spacetime). We also describe how QFTs can be coupled to extrinsic backgrounds for symmetry groups that differ from the intrinsic symmetry acting faithfully on the theory. Finally, we provide a variety of examples, ranging from TQFTs (gapped systems) to gapless QFTs. Along the way, we stress that the \u201cobstruction to symmetry fractionalization\u201d discussed in some condensed matter literature is really an instance of 2-group global symmetry
Holographic memory using beam steering
A method, apparatus, and system provide the ability for storing holograms at high speed. A single laser diode emits a collimated laser beam to both write to and read from a photorefractice crystal. One or more liquid crystal beam steering spatial light modulators (BSSLMs) steer a reference beam, split from the collimated laser beam, at high speed to the photorefractive crystal
Primes and composites in the determinant Hosoya triangle
In this paper, we look at numbers of the form
. These numbers are the entries of a
triangular array called the \emph{determinant Hosoya triangle} which we denote
by . We discuss the divisibility properties of the above numbers
and their primality. We give a small sieve of primes to illustrate the density
of prime numbers in . Since the Fibonacci and Lucas numbers
appear as entries in , our research is an extension of the
classical questions concerning whether there are infinitely many Fibonacci or
Lucas primes. We prove that has arbitrarily large neighbourhoods
of composite entries. Finally we present an abundance of data indicating a very
high density of primes in .Comment: two figure
Ab initio theory and modeling of water
Water is of the utmost importance for life and technology. However, a
genuinely predictive ab initio model of water has eluded scientists. We
demonstrate that a fully ab initio approach, relying on the strongly
constrained and appropriately normed (SCAN) density functional, provides such a
description of water. SCAN accurately describes the balance among covalent
bonds, hydrogen bonds, and van der Waals interactions that dictates the
structure and dynamics of liquid water. Notably, SCAN captures the density
difference between water and ice I{\it h} at ambient conditions, as well as
many important structural, electronic, and dynamic properties of liquid water.
These successful predictions of the versatile SCAN functional open the gates to
study complex processes in aqueous phase chemistry and the interactions of
water with other materials in an efficient, accurate, and predictive, ab initio
manner
Lifshitz transition and van Hove singularity in a Topological Dirac Semimetal
A topological Dirac semimetal is a novel state of quantum matter which has
recently attracted much attention as an apparent 3D version of graphene. In
this paper, we report critically important results on the electronic structure
of the 3D Dirac semimetal Na3Bi at a surface that reveals its nontrivial
groundstate. Our studies, for the first time, reveal that the two 3D Dirac
cones go through a topological change in the constant energy contour as a
function of the binding energy, featuring a Lifshitz point, which is missing in
a strict 3D analog of graphene (in other words Na3Bi is not a true 3D analog of
graphene). Our results identify the first example of a band saddle point
singularity in 3D Dirac materials. This is in contrast to its 2D analogs such
as graphene and the helical Dirac surface states of a topological insulator.
The observation of multiple Dirac nodes in Na3Bi connecting via a Lifshitz
point along its crystalline rotational axis away from the Kramers point serves
as a decisive signature for the symmetry-protected nature of the Dirac
semimetal's topological groundstate.Comment: 5 pages, 4 Figures, Related papers on topological Fermi arcs and Weyl
Semimetals (WSMs) are at
http://physics.princeton.edu/zahidhasangroup/index.htm
Energy hole mitigation through cooperative transmission in wireless sensor networks
The energy balancing capability of cooperative communication is utilized to solve the energy hole problem in wireless sensor networks. We first propose a cooperative transmission strategy, where intermediate nodes participate in two cooperative multi-input single-output (MISO) transmissions with the node at the previous hop and a selected node at the next hop, respectively. Then, we study the optimization problems for power allocation of the cooperative transmission strategy by examining two different approaches: network lifetime maximization (NLM) and energy consumption minimization (ECM). For NLM, the numerical optimal solution is derived and a searching algorithm for suboptimal solution is provided when the optimal solution does not exist. For ECM, a closed-form solution is obtained. Numerical and simulation results show that both the approaches have much longer network lifetime than SISO transmission strategies and other cooperative communication schemes. Moreover, NLM which features energy balancing outperforms ECM which focuses on energy efficiency, in the network lifetime sense
Scalar-Torsion Mode in a Cosmological Model of the Poincar\'{e} Gauge Theory of Gravity
We investigate the equation of state (EoS) of the scalar-torsion mode in
Poincar\'{e} gauge theory of gravity. We concentrate on two cases with the
constant curvature solution and positive kinetic energy, respectively. In the
former, we find that the torsion EoS has different values in the various stages
of the universe. In particular, it behaves like the radiation (matter) EoS of
() in the radiation (matter) dominant epoch, while in the late
time the torsion density is supportive for the accelerating universe. In the
latter, our numerical analysis shows that in general the EoS has an asymptotic
behavior in the high redshift regime, while it could cross the phantom divide
line in the low redshift regime.Comment: 12 pages, 2 figures, title changed, revised version accepted for
publication in JCA
Supercooled Water and the Kinetic Glass Transition II: Collective Dynamics
In this article we study in detail the Q-vector dependence of the collective
dynamics in simulated deeply supercooled SPC/E water. The evolution of the
system has been followed for 250 ns at low T, allowing a clear identification
of a two step relaxation process. We present evidence in favor of the use of
the mode coupling theory for supercooled liquid as framework for the
description of the slow alpha-relaxation dynamics in SPC/E water,
notwithstanding the fact that the cage formation in this system is controlled
by the formation of an open network of hydrogen bonds as opposed to packing
constraints, as in the case of simple liquids.Comment: rev-tex + 9 figure
Mass Determination in SUSY-like Events with Missing Energy
We describe a kinematic method which is capable of determining the overall
mass scale in SUSY-like events at a hadron collider with two missing (dark
matter) particles. We focus on the kinematic topology in which a pair of
identical particles is produced with each decaying to two leptons and an
invisible particle (schematically, followed by each
decaying via where is invisible). This topology
arises in many SUSY processes such as squark and gluino production and decay,
not to mention t\anti t di-lepton decays. In the example where the final
state leptons are all muons, our errors on the masses of the particles ,
and in the decay chain range from 4 GeV for 2000 events after cuts to 13
GeV for 400 events after cuts. Errors for mass differences are much smaller.
Our ability to determine masses comes from considering all the kinematic
information in the event, including the missing momentum, in conjunction with
the quadratic constraints that arise from the , and mass-shell
conditions. Realistic missing momentum and lepton momenta uncertainties are
included in the analysis.Comment: 41 pages, 14 figures, various clarifications and expanded discussion
included in revised version that conforms to the version to be publishe
Herschel HIFI observations of O toward Orion: special conditions for shock enhanced emission
We report observations of molecular oxygen (O) rotational transitions at
487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and
774 GHz are detected at velocities of 10-12 km/s with line widths 3 km/s;
however, the transition at 1121 GHz is not detected. The observed line
characteristics, combined with the results of earlier observations, suggest
that the region responsible for the O emission is 9" (6e16 cm) in size, and
is located close to the H2 Peak 1position (where vibrationally-excited H
emission peaks), and not at Peak A, 23" away. The peak O2 column density is
1.1e18/cm2. The line velocity is close to that of 621 GHz water maser emission
found in this portion of the Orion Molecular Cloud, and having a shock with
velocity vector lying nearly in the plane of the sky is consistent with
producing maximum maser gain along the line-of-sight. The enhanced O
abundance compared to that generally found in dense interstellar clouds can be
explained by passage of a low-velocity C-shock through a clump with preshock
density 2e4/cm3, if a reasonable flux of UV radiation is present. The postshock
O can explain the emission from the source if its line of sight dimension
is ~10 times larger than its size on the plane of the sky. The special geometry
and conditions required may explain why O emission has not been detected in
the cores of other massive star-forming molecular clouds.Comment: 28 pages, 13 figure
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