8,148 research outputs found
Comment on "Orientational Distribution of Free O-H Groups of Interfacial Water is Exponential"
In a recent letter (PRL,121,246101,2018), Sun et al. reported that combined
MD simulation and sum frequency generation vibrational spectroscopy (SFG-VS)
measurements led to conclusions of a broad and exponentially decaying
orientational distribution, and the presence of the free O-H group pointing
down to the bulk at the air/water interface. In this comment, we show that
their main conclusions are based on questionable interpretation of the SFG-VS
data presented in the letter [1], and are also contrary to the established data
analysis and interpretations in the literature [2-5].Comment: 2 pages, 0 figure
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The Random-Query Model and the Memory-Bounded Coupon Collector
We study a new model of space-bounded computation, the random-query model. The model is based on a branching-program over input variables x_1,…,x_n. In each time step, the branching program gets as an input a random index i ∈ {1,…,n}, together with the input variable x_i (rather than querying an input variable of its choice, as in the case of a standard (oblivious) branching program). We motivate the new model in various ways and study time-space tradeoff lower bounds in this model. Our main technical result is a quadratic time-space lower bound for zero-error computations in the random-query model, for XOR, Majority and many other functions. More precisely, a zero-error computation is a computation that stops with high probability and such that conditioning on the event that the computation stopped, the output is correct with probability 1. We prove that for any Boolean function f: {0,1}^n → {0,1}, with sensitivity k, any zero-error computation with time T and space S, satisfies T ⋅ (S+log n) ≥ Ω(n⋅k). We note that the best time-space lower bounds for standard oblivious branching programs are only slightly super linear and improving these bounds is an important long-standing open problem. To prove our results, we study a memory-bounded variant of the coupon-collector problem that seems to us of independent interest and to the best of our knowledge has not been studied before. We consider a zero-error version of the coupon-collector problem. In this problem, the coupon-collector could explicitly choose to stop when he/she is sure with zero-error that all coupons have already been collected. We prove that any zero-error coupon-collector that stops with high probability in time T, and uses space S, satisfies T⋅(S+log n) ≥ Ω(n^2), where n is the number of different coupons
Standard Model Effective Field Theory: Integrating out a Generic Scalar
We consider renormalisable models extended in the scalar sector by a generic
scalar field in addition to the standard model Higgs boson field, and work out
the effective theory for the latter in the decoupling limit. We match the full
theory onto the effective theory at tree and one-loop levels, and concentrate
on dimension-6 operators of the Higgs and electroweak gauge fields induced from
such matching. The Wilson coefficients of these dimension-6 operators from
tree-level matching are further improved by renormalisation group running. For
specific representations of the scalar field, some "accidental"
couplings with the Higgs field are allowed and can lead to dimension-6
operators at tree and/or one-loop level. Otherwise, two types of interaction
terms are identified to have only one-loop contributions, for the Wilson
coefficients of which we have obtained a general formula. Using the obtained
results, we analyse constraints from electroweak oblique parameters and the
Higgs data on several phenomenological models.Comment: corrections on RGE improvemen
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