Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How large can the branching ratio of $B_s \to \tau^+ \tau^-$ be ?   Motivated by the large like-sign dimuon charge asymmetry observed recently,
whose explanation would require an enhanced decay rate of $B_s \to \tau^+
\tau^-$, we explore how large a branching ratio of this decay mode is allowed
by the present constraints. We use bounds from the lifetimes of $B_d$ and
$B_s$, constraints from the branching ratios of related $b \to s \tau^+ \tau^-$
modes, as well as measurements of the mass difference, width difference and
CP-violating phase in the $B_s$-$\bar{B}_s$ system. Using an effective field
theory approach, we show that a branching ratio as high as 15% may be allowed
while being consistent with the above constraints. The model with a scalar
leptoquark cannot increase the branching ratio to a per cent level. However, an
enhancement up to 5% is possible in the model with an extremely light $Z'$ with
flavor-dependent interactions, even after all the couplings are taken to be
perturbative. This however cannot account for the dimuon anomaly completely by
itself.

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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: adap-org
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The categories of this paper are: econ
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: supr-con
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The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-th
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The categories of this paper are: cs
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The categories of this paper are: gr-qc