210 research outputs found

### Dark Z implication for flavor physics

Dark $Z$/dark photon ($Z'$) is one candidate of dark force carrier, which
helps to interpret the properties of dark matter (DM). Other than traditional
studies of DM including direct detection, indirect detection and collider
simulation, in this work we take flavor physics as a complementary approach to
investigate the features of dark matter. We give an exact calculation of the
new type of penguin diagram induced by $Z'$ which further modifies the
well-known $X, Y, Z$ functions in penguin-box expansion. The measurement of
rare decays $B\to K^{(*)}\mu^+\mu^-$ and $B_s\to \mu^+\mu^-$ at LHC, together
with direct CP violation $\varepsilon'/\varepsilon$ in $K\to\pi \pi$ as well as
$K_L\to\mu^+\mu^-$, are used to determine the parameter space. The size of
coupling constant, however, is found to be $\mathcal{O}(1)$ which is much
weaker than the known constraints.Comment: 13 pages, 3 figures; For V2 typo corrected, references added,
published in JHE

### Correlating $B_q^0 \to \mu^+\mu^-$ and $K_L \to \pi^0\nu\bar\nu$ Decays with Four Generations

The long-awaited $B_s\to \mu^+\mu^-$ mode has finally been observed at rate
consistent with Standard Model, albeit lower by 1.2$\sigma$. There is some hint
for New Physics in the rarer $B_d^0 \to \mu^+\mu^-$ decay, especially if the
currently 2.2$\sigma$-enhanced central value persists with more data. The
measurement of $CP$ violating phase $\phi_s$, via both $B_s\to J/\psi K\bar K$
and $J/\psi\pi\pi$ modes, has reached Standard Model sensitivity. These
measurements stand major improvement when LHC enters Run 2. Concurrently, the
$K_L\to\pi^0\nu\bar\nu$ and $K^+\to\pi^+\nu\bar\nu$ modes are being pursued in
a similar time frame. We illustrate the possible correlations between New
Physics effects in these four modes, using the fourth generation as example.
While correlations may or may not exist in other New Physics models, the four
generation model can accommodate enhancements in both $B_d^0 \to \mu^+\mu^-$
and $K_L\to\pi^0\nu\bar\nu$.Comment: 9 pages, 5 figures for V1; for V2 title modified, minor changes
performed to figures, part of contents revised to 7 pages, note added, one of
the authors' affiliation changed, accepted for the publication of PL

### Matter Effects of Sterile Neutrino in Light of Renormalization-Group Equations

The renormalization-group equation (RGE) approach to neutrino matter effects
is further developed in this work. We derive a complete set of differential
equations for effective mixing elements, masses and Jarlskog-like invariants in
presence of a light sterile neutrino. The evolutions of mixing elements as well
as Jarlskog-like invariants are obtained by numerically solving these
differential equations. We calculate terrestrial matter effects in
long-baseline (LBL) experiments, taking NOvA, T2K and DUNE as examples. In both
three-flavor and four-flavor frameworks, electron-neutrino survival
probabilities as well as the day-night asymmetry of solar neutrino are also
evaluated as a further examination of the RGE approach.Comment: 18 pages, 3 figures, 1 table; 22 pages, the version accepted by JHE

### The Global Fits of New Physics in $b \to s$ after $R_{K^{(*)}}$ 2022 Release

The measurement of lepton universality parameters $R_{K^{(*)}}$ was updated
by LHCb in December 2022, which indicated that the well-known anomalies in
flavor-changing neutral current (FCNC) processes of B meson decays have faded
away. However, does this mean that all new physics possibilities related to
$b\to s\ell^+\ell^-$ have been excluded? We aim to answer this question in this
work. The state-of-the-art effective Hamiltonian is adopted to describe $b \to
s$ transition, while BSM (beyond the Standard Model) new physics effects are
encoded in Wilson coefficients (WCs). Using around 200 observables in leptonic
and semileptonic decays of B mesons and bottom baryons, measured by LHCb, CMS,
ATLAS, Belle, and BaBar, we perform global fits of these Wilson coefficients in
four different scenarios. In particular, lepton flavors in WCs are specified in
some of the working scenarios. To see the change of new physics parameters, we
use both the data before and after the 2022 release of $R_{K^{(*)}}$ in two
separate sets of fits. We find that in all four scenarios, $\Delta C_9^\mu$
still has a deviation more than $4\sigma$ from the Standard Model. At the
$1\sigma$ level, the lepton flavor in WCs is distinguishable for $\Delta C_{9,
S, P}$ but indistinguishable for $\Delta C_{10}$. We demonstrate numerically
that there is no chirality for muon type of scalar operator and it is kept at
the $1\sigma$ level for their electron type dual ones, while chiral difference
exists for $\mathcal{O}_{9,10}^\mu$ at least at the $2\sigma$ level.Comment: 36 pages, 27 figure

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