29,498 research outputs found
Tri-bimaximal Neutrino Mixing from A(4) and \theta_{13} \sim \theta_C
It is a common believe that, if the Tri-bimaximal mixing (TBM) pattern is
explained by vacuum alignment in an A(4) model, only a very small reactor
angle, say \theta_{13} \sim \lambda^2_C being \lambda_C \equiv \theta_C the
Cabibbo angle, can be accommodated. This statement is based on the assumption
that all the flavon fields acquire VEVs at a very similar scale and the
departures from exact TBM arise at the same perturbation level. From the
experimental point of view, however, a relatively large value \theta_{13} \sim
\lambda_C is not yet excluded by present data. In this paper, we propose a
Seesaw A(4) model in which the previous assumption can naturally be evaded. The
aim is to describe a \theta_{13} \sim \lambda_C without conflicting with the
TBM prediction for \theta_{12} which is rather close to the observed value (at
\lambda^2_C level). In our model the deviation of the atmospherical angle from
maximal is subject to the sum-rule: \sin ^2 \theta_{23} \approx 1/2 +
\sqrt{2}/2 \sin \delta \cos \theta_{13} which is a next-to-leading order
prediction of our model.Comment: 16 pages, revised, typos corrected, references adde
Run Generation Revisited: What Goes Up May or May Not Come Down
In this paper, we revisit the classic problem of run generation. Run
generation is the first phase of external-memory sorting, where the objective
is to scan through the data, reorder elements using a small buffer of size M ,
and output runs (contiguously sorted chunks of elements) that are as long as
possible.
We develop algorithms for minimizing the total number of runs (or
equivalently, maximizing the average run length) when the runs are allowed to
be sorted or reverse sorted. We study the problem in the online setting, both
with and without resource augmentation, and in the offline setting.
(1) We analyze alternating-up-down replacement selection (runs alternate
between sorted and reverse sorted), which was studied by Knuth as far back as
1963. We show that this simple policy is asymptotically optimal. Specifically,
we show that alternating-up-down replacement selection is 2-competitive and no
deterministic online algorithm can perform better.
(2) We give online algorithms having smaller competitive ratios with resource
augmentation. Specifically, we exhibit a deterministic algorithm that, when
given a buffer of size 4M , is able to match or beat any optimal algorithm
having a buffer of size M . Furthermore, we present a randomized online
algorithm which is 7/4-competitive when given a buffer twice that of the
optimal.
(3) We demonstrate that performance can also be improved with a small amount
of foresight. We give an algorithm, which is 3/2-competitive, with
foreknowledge of the next 3M elements of the input stream. For the extreme case
where all future elements are known, we design a PTAS for computing the optimal
strategy a run generation algorithm must follow.
(4) Finally, we present algorithms tailored for nearly sorted inputs which
are guaranteed to have optimal solutions with sufficiently long runs
Tri-bimaximal Neutrino Mixing and Quark Masses from a Discrete Flavour Symmetry
We build a supersymmetric model of quark and lepton masses based on the
discrete flavour symmetry group T', the double covering of A_4. In the lepton
sector our model is practically indistinguishable from recent models based on
A_4 and, in particular, it predicts a nearly tri-bimaximal mixing, in good
agreement with present data. In the quark sector a realistic pattern of masses
and mixing angles is obtained by exploiting the doublet representations of T',
not available in A_4. To this purpose, the flavour symmetry T' should be broken
spontaneously along appropriate directions in flavour space. In this paper we
fully discuss the related vacuum alignment problem, both at the leading order
and by accounting for small effects coming from higher-order corrections. As a
result we get the relations: \sqrt{m_d/m_s}\approx |V_{us}| and
\sqrt{m_d/m_s}\approx |V_{td}/V_{ts}|.Comment: 27 pages, 1 figure; minor correction
Tri-Bimaximal Lepton Mixing and Leptogenesis
In models with flavour symmetries added to the gauge group of the Standard
Model the CP-violating asymmetry necessary for leptogenesis may be related with
low-energy parameters. A particular case of interest is when the flavour
symmetry produces exact Tri-Bimaximal lepton mixing leading to a vanishing
CP-violating asymmetry. In this paper we present a model-independent discussion
that confirms this always occurs for unflavoured leptogenesis in type I see-saw
scenarios, noting however that Tri-Bimaximal mixing does not imply a vanishing
asymmetry in general scenarios where there is interplay between type I and
other see-saws. We also consider a specific model where the exact Tri-Bimaximal
mixing is lifted by corrections that can be parametrised by a small number of
degrees of freedom and analyse in detail the existing link between low and
high-energy parameters - focusing on how the deviations from Tri-Bimaximal are
connected to the parameters governing leptogenesis.Comment: 29 pages, 6 figures; version 2: references added, minor correction
Lepton Flavour Violation in a Supersymmetric Model with A4 Flavour Symmetry
We compute the branching ratios for mu-> e gamma, tau-> mu gamma and tau -> e
gamma in a supersymmetric model invariant under the flavour symmetry group A4 X
Z3 X U(1)_{FN}, in which near tri-bimaximal lepton mixing is naturally
predicted. At leading order in the small symmetry breaking parameter u, which
is of the same order as the reactor mixing angle theta_{13}, we find that the
branching ratios generically scale as u^2. Applying the current bound on the
branching ratio of mu -> e gamma shows that small values of u or tan(beta) are
preferred in the model for mass parameters m_{SUSY} and m_{1/2} smaller than
1000 GeV. The bound expected from the on-going MEG experiment will provide a
severe constraint on the parameter space of the model either enforcing u approx
0.01 and small tan(beta) or m_{SUSY} and m_{1/2} above 1000 GeV. In the special
case of universal soft supersymmetry breaking terms in the flavon sector a
cancellation takes place in the amplitudes and the branching ratios scale as
u^4, allowing for smaller slepton masses. The branching ratios for tau -> mu
gamma and tau -> e gamma are predicted to be of the same order as the one for
mu -> e gamma, which precludes the possibility of observing these tau decays in
the near future.Comment: 44 page
Nonadditive entropy for random quantum spin-S chains
We investigate the scaling of Tsallis entropy in disordered quantum spin-S
chains. We show that an extensive scaling occurs for specific values of the
entropic index. Those values depend only on the magnitude S of the spins, being
directly related with the effective central charge associated with the model.Comment: 5 pages, 7 figures. v3: Minor corrections and references updated.
Published versio
Improving Outfit Recommendation with Co-supervision of Fashion Generation
The task of fashion recommendation includes two main challenges: visual
understanding and visual matching. Visual understanding aims to extract
effective visual features. Visual matching aims to model a human notion of
compatibility to compute a match between fashion items. Most previous studies
rely on recommendation loss alone to guide visual understanding and matching.
Although the features captured by these methods describe basic characteristics
(e.g., color, texture, shape) of the input items, they are not directly related
to the visual signals of the output items (to be recommended). This is
problematic because the aesthetic characteristics (e.g., style, design), based
on which we can directly infer the output items, are lacking. Features are
learned under the recommendation loss alone, where the supervision signal is
simply whether the given two items are matched or not. To address this problem,
we propose a neural co-supervision learning framework, called the FAshion
Recommendation Machine (FARM). FARM improves visual understanding by
incorporating the supervision of generation loss, which we hypothesize to be
able to better encode aesthetic information. FARM enhances visual matching by
introducing a novel layer-to-layer matching mechanism to fuse aesthetic
information more effectively, and meanwhile avoiding paying too much attention
to the generation quality and ignoring the recommendation performance.
Extensive experiments on two publicly available datasets show that FARM
outperforms state-of-the-art models on outfit recommendation, in terms of AUC
and MRR. Detailed analyses of generated and recommended items demonstrate that
FARM can encode better features and generate high quality images as references
to improve recommendation performance
- …