2,356 research outputs found
Instabilities of the Small Black Hole: a view from N=4 SYM
We compute a one-loop effective action for the constant modes of the scalars
and the Polyakov loop matrix of N=4 SYM on S^3 at finite temperature and weak
't Hooft coupling. Above a critical temperature, the effective potential
develops new unstable directions accompanied by new saddle points which only
preserve an SO(5) subgroup of the SO(6) global R-symmetry. We identify this
phenomenon as the weak coupling version of the well known Gregory-Laflamme
localization instability in the gravity dual of the strongly coupled field
theory: The small AdS_5 black hole when viewed as a ten dimensional,
asymptotically AdS_5 X S^5 solution smeared on the S^5 is unstable to
localization on S^5. Our effective potential, in a specific Lorentzian
continuation, can provide a qualitative holographic description of the decay of
the "topological black hole'' into the AdS bubble of nothing.Comment: 39 pages, 6 figures, uses JHEP3.cls, references adde
RCD: Rapid Close to Deadline Scheduling for Datacenter Networks
Datacenter-based Cloud Computing services provide a flexible, scalable and
yet economical infrastructure to host online services such as multimedia
streaming, email and bulk storage. Many such services perform geo-replication
to provide necessary quality of service and reliability to users resulting in
frequent large inter- datacenter transfers. In order to meet tenant service
level agreements (SLAs), these transfers have to be completed prior to a
deadline. In addition, WAN resources are quite scarce and costly, meaning they
should be fully utilized. Several recently proposed schemes, such as B4,
TEMPUS, and SWAN have focused on improving the utilization of inter-datacenter
transfers through centralized scheduling, however, they fail to provide a
mechanism to guarantee that admitted requests meet their deadlines. Also, in a
recent study, authors propose Amoeba, a system that allows tenants to define
deadlines and guarantees that the specified deadlines are met, however, to
admit new traffic, the proposed system has to modify the allocation of already
admitted transfers. In this paper, we propose Rapid Close to Deadline
Scheduling (RCD), a close to deadline traffic allocation technique that is fast
and efficient. Through simulations, we show that RCD is up to 15 times faster
than Amoeba, provides high link utilization along with deadline guarantees, and
is able to make quick decisions on whether a new request can be fully satisfied
before its deadline.Comment: World Automation Congress (WAC), IEEE, 201
N=4 SYM on S^3 with Near Critical Chemical Potentials
We study the N = 4 theory at weak coupling, on a three sphere in the grand
canonical ensemble with R symmetry chemical potentials. We focus attention on
near critical values for the chemical potentials, above which the classical
theory has no ground state. By computing a one loop effective potential for the
light degrees of freedom in this regime, we show the existence of flat
directions of complex dimension N, 2N and 3N for one, two and three critical
chemical potentials respectively; these correspond to one half, one quarter and
one-eighth BPS states becoming light respectively at the critical values. At
small finite temperature we show that the chemical potentials can be continued
beyond their classical limiting values to yield a deconfined metastable phase
with lifetime diverging in the large N limit. Our low temperaure analysis
complements the high temperature metastability found by Yamada and Yaffe. The
resulting phase diagram at weak coupling bears a striking resemblance to the
strong coupling phase diagram for charged AdS black holes. Our analysis also
reveals subtle qualitative differences between the two regimes.Comment: 34 pages, 4 figure
Embedded Eigenvalues and the Nonlinear Schrodinger Equation
A common challenge to proving asymptotic stability of solitary waves is
understanding the spectrum of the operator associated with the linearized flow.
The existence of eigenvalues can inhibit the dispersive estimates key to
proving stability. Following the work of Marzuola & Simpson, we prove the
absence of embedded eigenvalues for a collection of nonlinear Schrodinger
equations, including some one and three dimensional supercritical equations,
and the three dimensional cubic-quintic equation. Our results also rule out
nonzero eigenvalues within the spectral gap and, in 3D, endpoint resonances.
The proof is computer assisted as it depends on the sign of certain inner
products which do not readily admit analytic representations. Our source code
is available for verification at
http://www.math.toronto.edu/simpson/files/spec_prop_asad_simpson_code.zip.Comment: 29 pages, 27 figures: fixed a typo in an equation from the previous
version, and added two equations to clarif
Long range magnetic ordering in a spin-chain compound, CaCuMnO, with multiple bond distances
The results of ac and dc magnetization and heat capacity measurements as a
function of temperature (T = 1.8 to 300 K) are reported for a
quasi-one-dimensional compound, CaCuMnO, crystallizing in a
triclinically distorted KCdCl-type structure. The results reveal that
this compound undergoes antiferromagnetic ordering close to 5.5 K. In addition,
there is another magnetic transition below 3.6 K. Existence of two long-range
magnetic transitions is uncommon among quasi-one-dimensional systems. It is
interesting to note that both the magnetic transitions are of long-range type,
instead of spin-glass type, in spite of the fact that the Cu-O and Mn-O bond
distances are multiplied due to this crystallographic distortion. In view of
this, this compound could serve as a nice example for studying
"order-in-disorder" phenomena.Comment: Physical Review (in press
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