4,160 research outputs found
Implementation in Advised Strategies: Welfare Guarantees from Posted-Price Mechanisms When Demand Queries Are NP-Hard
State-of-the-art posted-price mechanisms for submodular bidders with
items achieve approximation guarantees of [Assadi and
Singla, 2019]. Their truthfulness, however, requires bidders to compute an
NP-hard demand-query. Some computational complexity of this form is
unavoidable, as it is NP-hard for truthful mechanisms to guarantee even an
-approximation for any [Dobzinski and
Vondr\'ak, 2016]. Together, these establish a stark distinction between
computationally-efficient and communication-efficient truthful mechanisms.
We show that this distinction disappears with a mild relaxation of
truthfulness, which we term implementation in advised strategies, and that has
been previously studied in relation to "Implementation in Undominated
Strategies" [Babaioff et al, 2009]. Specifically, advice maps a tentative
strategy either to that same strategy itself, or one that dominates it. We say
that a player follows advice as long as they never play actions which are
dominated by advice. A poly-time mechanism guarantees an -approximation
in implementation in advised strategies if there exists poly-time advice for
each player such that an -approximation is achieved whenever all
players follow advice. Using an appropriate bicriterion notion of approximate
demand queries (which can be computed in poly-time), we establish that (a
slight modification of) the [Assadi and Singla, 2019] mechanism achieves the
same -approximation in implementation in advised
strategies
On the Role of Charmed Meson Loops in Charmonium Decays
We investigate the effect of intermediate charmed meson loops on the M1
radiative decays and
as well as the isospin violating
hadronic decays using heavy hadron
chiral perturbation theory (HHPT). The calculations include tree level as
well as one loop diagrams and are compared to the latest data from CLEO and
BES-III. Our fit constrains the couplings of 1S and 2S charmonium multiplets to
charmed mesons, denoted and , respectively. We find that
there are two sets of solutions for and . One set, which
agrees with previous values of the product extracted from
analyses that consider only loop contributions to , can only fit data on radiative decays with fine-tuned
cancellations between tree level diagrams and loops in that process. The other
solution for and leads to couplings that are smaller by a
factor of 2.3. In this case tree level and loop contributions are of comparable
size and the numerical values of the tree level contributions to radiative
decays are consistent with estimates based on the quark model as well as
non-relativistic QCD (NRQCD). This result shows that tree level HHPT
couplings are as important as the one loop graphs with charmed mesons in these
charmonium decays. The couplings and are also important for
the calculations of the decays of charmed meson bound states, such as the
X(3872), to conventional charmonia.Comment: 16 pages, 3 figures, minor modifications, more references adde
A Classification and Analysis of Higgs-flavor Models
A classification is given of Higgs-flavor models. In these models, there are
several Higgs doublets in an irreducible multiplet R_{Phi} of a non-abelian
symmetry G_{Phi}, under which the quarks and leptons do not transform (thus
giving minimal flavor-changing for the fermions). It is found that different
G_{Phi} and R_{Phi} lead to very distinctive spectra of the extra Higgs
doublets, including different numbers of "sequential Higgs" and of "inert
Higgs" that could play the role of dark matter, different mass relations, and
different patterns of SU(2)_L-breaking splittings within the Higgs doublets.Comment: 35 page
Emergence of supersymmetry on the surface of three dimensional topological insulators
We propose two possible experimental realizations of a 2+1 dimensional
spacetime supersymmetry at a quantum critical point on the surface of three
dimensional topological insulators. The quantum critical point between the
semi-metallic state with one Dirac fermion and the s-wave superconducting state
on the surface is described by a supersymmetric conformal field theory within
-expansion. We predict the exact voltage dependence of the
differential conductance at the supersymmetric critical point.Comment: 8 pages, 2 figures; published versio
Regularization, Renormalization and Range: The Nucleon-Nucleon Interaction from Effective Field Theory
Regularization and renormalization is discussed in the context of low-energy
effective field theory treatments of two or more heavy particles (such as
nucleons). It is desirable to regulate the contact interactions from the outset
by treating them as having a finite range. The low energy physical observables
should be insensitive to this range provided that the range is of a similar or
greater scale than that of the interaction. Alternative schemes, such as
dimensional regularization, lead to paradoxical conclusions such as the
impossibility of repulsive interactions for truly low energy effective theories
where all of the exchange particles are integrated out. This difficulty arises
because a nonrelativistic field theory with repulsive contact interactions is
trivial in the sense that the matrix is unity and the renormalized coupling
constant zero. Possible consequences of low energy attraction are also
discussed. It is argued that in the case of large or small scattering lengths,
the region of validity of effective field theory expansion is much larger if
the contact interactions are given a finite range from the beginning.Comment: 7 page
General Properties of the Gravitational Wave Spectrum from Phase Transitions
In this paper we discuss some general aspects of the gravitational wave
background arising from post-inflationary short-lasting cosmological events
such as phase transitions. We concentrate on the physics which determines the
shape and the peak frequency of the gravitational wave spectrum. We then apply
our general findings to the case of bubble collisions during a first order
phase transition and compare different results in the recent literature.Comment: 11 pages, 8 figures; v2: minor clarifications, published versio
Lorentz transformations that entangle spins and entangle momenta
Simple examples are presented of Lorentz transformations that entangle the
spins and momenta of two particles with positive mass and spin 1/2. They apply
to indistinguishable particles, produce maximal entanglement from finite
Lorentz transformations of states for finite momenta, and describe entanglement
of spins produced together with entanglement of momenta. From the entanglements
considered, no sum of entanglements is found to be unchanged.Comment: 5 Pages, 2 Figures, One new paragraph and reference adde
Fluctuations in the Cosmic Microwave Background I: Form Factors and their Calculation in Synchronous Gauge
It is shown that the fluctuation in the temperature of the cosmic microwave
background in any direction may be evaluated as an integral involving scalar
and dipole form factors, which incorporate all relevant information about
acoustic oscillations before the time of last scattering. A companion paper
gives asymptotic expressions for the multipole coefficient in terms of
these form factors. Explicit expressions are given here for the form factors in
a simplified hydrodynamic model for the evolution of perturbations.Comment: 35 pages, no figures. Improved treatment of damping, including both
Landau and Silk damping; inclusion of late-time effects; several references
added; minor changes and corrections made. Accepted for publication in Phys.
Rev. D1
Decentralized Reinforcement Learning: Global Decision-Making via Local Economic Transactions
This paper seeks to establish a framework for directing a society of simple,
specialized, self-interested agents to solve what traditionally are posed as
monolithic single-agent sequential decision problems. What makes it challenging
to use a decentralized approach to collectively optimize a central objective is
the difficulty in characterizing the equilibrium strategy profile of
non-cooperative games. To overcome this challenge, we design a mechanism for
defining the learning environment of each agent for which we know that the
optimal solution for the global objective coincides with a Nash equilibrium
strategy profile of the agents optimizing their own local objectives. The
society functions as an economy of agents that learn the credit assignment
process itself by buying and selling to each other the right to operate on the
environment state. We derive a class of decentralized reinforcement learning
algorithms that are broadly applicable not only to standard reinforcement
learning but also for selecting options in semi-MDPs and dynamically composing
computation graphs. Lastly, we demonstrate the potential advantages of a
society's inherent modular structure for more efficient transfer learning.Comment: 18 pages, 13 figures, accepted to the International Conference on
Machine Learning (ICML) 202
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