174 research outputs found
Averaged Null Energy Condition from Causality
Unitary, Lorentz-invariant quantum field theories in flat spacetime obey
microcausality: commutators vanish at spacelike separation. For interacting
theories in more than two dimensions, we show that this implies that the
averaged null energy, , must be positive. This non-local
operator appears in the operator product expansion of local operators in the
lightcone limit, and therefore contributes to -point functions. We derive a
sum rule that isolates this contribution and is manifestly positive. The
argument also applies to certain higher spin operators other than the stress
tensor, generating an infinite family of new constraints of the form . These lead to new inequalities for the coupling
constants of spinning operators in conformal field theory, which include as
special cases (but are generally stronger than) the existing constraints from
the lightcone bootstrap, deep inelastic scattering, conformal collider methods,
and relative entropy. We also comment on the relation to the recent derivation
of the averaged null energy condition from relative entropy, and suggest a more
general connection between causality and information-theoretic inequalities in
QFT.Comment: 31+8 page
A Conformal Collider for Holographic CFTs
We develop a formalism to study the implications of causality on OPE
coefficients in conformal field theories with large central charge and a sparse
spectrum of higher spin operators. The formalism has the interpretation of a
new conformal collider-type experiment for these class of CFTs and hence it has
the advantage of requiring knowledge only about CFT three-point functions. This
is accomplished by considering the holographic null energy operator which was
introduced in arXiv:1709.03597 as a generalization of the averaged null energy
operator. Analyticity properties of correlators in the Regge limit imply that
the holographic null energy operator is a positive operator in a subspace of
the total CFT Hilbert space. Utilizing this positivity condition, we derive
bounds on three-point functions of the stress tensor
with various operators for CFTs with large central charge and a sparse
spectrum. After imposing these constraints, we also find that the operator
product expansions of all primary operators in the Regge limit have certain
universal properties. All of these results are consistent with the expectation
that CFTs in this class, irrespective of their microscopic details, admit
universal gravity-like holographic dual descriptions. Furthermore, this
connection enables us to constrain various inflationary observables such as the
amplitude of chiral gravity waves, non-gaussanity of gravity waves and
tensor-to-scalar ratio.Comment: 52+15 pages, 5 figure
Einstein gravity 3-point functions from conformal field theory
We study stress tensor correlation functions in four-dimensional conformal
field theories with large and a sparse spectrum. Theories in this class are
expected to have local holographic duals, so effective field theory in anti-de
Sitter suggests that the stress tensor sector should exhibit universal,
gravity-like behavior. At the linearized level, the hallmark of locality in the
emergent geometry is that stress tensor three-point functions , normally specified by three constants, should approach a universal
structure controlled by a single parameter as the gap to higher spin operators
is increased. We demonstrate this phenomenon by a direct CFT calculation.
Stress tensor exchange, by itself, violates causality and unitarity unless the
three-point functions are carefully tuned, and the unique consistent choice
exactly matches the prediction of Einstein gravity. Under some assumptions
about the other potential contributions, we conclude that this structure is
universal, and in particular, that the anomaly coefficients satisfy as conjectured by Camanho et al. The argument is based on causality of a
four-point function, with kinematics designed to probe bulk locality, and
invokes the chaos bound of Maldacena, Shenker, and Stanford.Comment: 24+9 pages; minor changes, conclusions unchange
Men-in-the-Middle Attack Simulation on Low Energy Wireless Devices using Software Define Radio
The article presents a method which organizes men-in-the-middle attack and penetration test on Bluetooth Low Energy devices and ZigBee packets by using software define radio with sniffing and spoofing packets, capture and analysis techniques on wireless waves with the focus on BLE. The paper contains the analysis of the latest scientific works in this area, provides a comparative analysis of SDRs with the rationale for the choice of hardware, gives the sequence order of actions for collecting wireless data packets and data collection from ZigBee and BLE devices, and analyzes ways which can improve captured wireless packet analysis techniques. The results of the experimental setup, collected for the study, were analyzed in real time and the collected wireless data packets were compared with the one, which have sent the origin. The result of the experiment shows the weaknesses of local wireless networks
Minimax Optimal Submodular Optimization with Bandit Feedback
We consider maximizing a monotonic, submodular set function under stochastic bandit feedback. Specifically, is
unknown to the learner but at each time the learner chooses a set
with and receives reward
where is mean-zero sub-Gaussian noise. The objective is to minimize
the learner's regret over times with respect to ()-approximation
of maximum with , obtained through greedy maximization of
. To date, the best regret bound in the literature scales as . And by trivially treating every set as a unique arm one deduces that
is also achievable. In this work, we establish the
first minimax lower bound for this setting that scales like
. Moreover, we
propose an algorithm that is capable of matching the lower bound regret
- …