Quantum entanglement of weak interaction gauge bosons produced at colliders can be explored by computing the corresponding polarization density matrix. To this end, we consider the Higgs boson decays
...H
→
W
W
∗
and
H
→
Z
Z
∗
, in which
W
∗
and
Z
∗
are off-shell states, and the
WW
,
WZ
and
ZZ
di-boson production in proton collisions. The polarization density matrix of the di-boson state is determined by the amplitude of the production process and can be experimentally reconstructed from the angular distribution of the momenta of the final states into which the gauge bosons decay. We show that a suitable instance of the Bell inequality is violated in
H
→
Z
Z
∗
to a degree that can be tested at the LHC with future data. The same Bell inequality is violated in the production of
WW
and
ZZ
boson pairs for invariant masses above 900 GeV and scattering angles close to
π
/
2
in the center of mass frame. LHC data in this case are not sufficient to establish the violation of the Bell inequality. We also analyze the prospects for detecting Bell inequality violations in di-boson final states at future
e
+
e
-
and muon colliders. A further observable that provides a lower bound on the amount of polarization entanglement in the di-boson system is computed for each of the examined processes. The analytic expressions for the polarization density matrices are presented in full in an Appendix. We also provide the unitary matrices required in the optimization procedure necessary in testing the Bell inequalities.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The measurement of quantum entanglement can provide a new and most sensitive probe to physics beyond the Standard Model. We use the concurrence of the top-quark pair spin states produced at colliders ...to constrain the magnetic dipole term in the coupling between top quark and gluons, that of
τ
-lepton pair spin states to bound contact interactions and that of
τ
-lepton pairs or two-photons spin states from the decay of the Higgs boson in trying to distinguish between CP-even and odd couplings. These four examples show the power of the new approach as well as its limitations. We show that differences in the entanglement in the top-quark and
τ
-lepton pair production cross sections can provide constraints better than those previously estimated from total cross sections or classical correlations. Instead, the final states in the decays of the Higgs boson remain maximally entangled even in the presence of CP-odd couplings and cannot be used to set bounds on new physics. We discuss the violation of Bell inequalities featured in all four processes.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
We compute the contribution of the decays
$$K_L \rightarrow \pi ^0 Q {\bar{Q}}$$
K
L
→
π
0
Q
Q
¯
and
$$K^+ \rightarrow \pi ^+ Q {\bar{Q}}$$
K
+
→
π
+
Q
Q
¯
, where
Q
is a dark fermion of the ...dark sector, to the measured widths for the rare decays
$$K^+\rightarrow \pi ^+ \nu {\bar{\nu }}$$
K
+
→
π
+
ν
ν
¯
and
$$K_L\rightarrow \pi ^0 \nu {\bar{\nu }}$$
K
L
→
π
0
ν
ν
¯
. The recent experimental limit for
$$\varGamma (K^+ \rightarrow \pi ^+ \nu {\bar{\nu }})$$
Γ
(
K
+
→
π
+
ν
ν
¯
)
from
NA62
sets a new and very strict bound on the dark-sector parameters. A branching ratio for
$$K_L \rightarrow \pi ^0 Q {\bar{Q}}$$
K
L
→
π
0
Q
Q
¯
within the reach of the
KOTO
sensitivity is possible. The Grossman–Nir bound is weakened by the asymmetric effect of the different kinematic cuts enforced by the NA62 and KOTO experiments. This last feature holds true for all models where the decay into invisible states takes place through a light or massless intermediate state.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
I review the main features and some of the theoretical attempts to explain the excess around an invariant mass of 750 GeV seen in 2015 at the LHC in the di-photon channel. As this hint to new physics ...has now all but disappeared from the higher-luminosity 2016 data, the statistical analysis nicely illustrates why only a high level of significance can be trusted in a discovery. The various explanations that has been suggested remain interesting examples of our current understanding of physics beyond the standard model and also of the challenging task of discriminating among them.
We discuss the possibility of exploring an unbroken U(1) gauge interaction in the dark sector by means of gravitational waves. Dark sector states charged under the dark force can give a macroscopic ...charge to astronomical bodies. Yet the requirement of having gravitationally bounded stars limits this charge to negligible values if the force has a sizeable strength. Gravitational tests are only possible if the dark force is weaker than gravity. By solving the Einstein-Maxwell field equations, we study in detail an explicit model for dark charge generation and separation in a neutron star. Charged states originate from the decay of neutrons inside the star into three dark fermions; we show that in this model the equation of state is consistent with limits on neutron star masses and tidal deformability. We find that while the dark force can be observed in binary mergers (making them an optimal observational test even though with limited precision), it is screened in binary pulsars (for which more precise data exist). The emitted radiation in the inspiral phase of a binary system is modified and the dark force tested at the level of the uncertainty of the experimental detection. The test covers a region where current limits on deviations from Newton inverse-squared law come from geophysical and laser-ranging observations.
We compute the contribution of the decays Formula omitted and Formula omitted, where Q is a dark fermion of the dark sector, to the measured widths for the rare decays Formula omitted and Formula ...omitted. The recent experimental limit for Formula omitted from NA62 sets a new and very strict bound on the dark-sector parameters. A branching ratio for Formula omitted within the reach of the KOTO sensitivity is possible. The Grossman-Nir bound is weakened by the asymmetric effect of the different kinematic cuts enforced by the NA62 and KOTO experiments. This last feature holds true for all models where the decay into invisible states takes place through a light or massless intermediate state.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract We compute the contribution of the decays $$K_L \rightarrow \pi ^0 Q {\bar{Q}}$$ KL→π0QQ¯ and $$K^+ \rightarrow \pi ^+ Q {\bar{Q}}$$ K+→π+QQ¯ , where Q is a dark fermion of the dark sector, ...to the measured widths for the rare decays $$K^+\rightarrow \pi ^+ \nu {\bar{\nu }}$$ K+→π+νν¯ and $$K_L\rightarrow \pi ^0 \nu {\bar{\nu }}$$ KL→π0νν¯ . The recent experimental limit for $$\varGamma (K^+ \rightarrow \pi ^+ \nu {\bar{\nu }})$$ Γ(K+→π+νν¯) from NA62 sets a new and very strict bound on the dark-sector parameters. A branching ratio for $$K_L \rightarrow \pi ^0 Q {\bar{Q}}$$ KL→π0QQ¯ within the reach of the KOTO sensitivity is possible. The Grossman–Nir bound is weakened by the asymmetric effect of the different kinematic cuts enforced by the NA62 and KOTO experiments. This last feature holds true for all models where the decay into invisible states takes place through a light or massless intermediate state.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
If the diphoton excess at 750 GeV hinted by the 2015 data at the LHC is explained in terms of a scalar resonance participating in the breaking of the electroweak symmetry, this resonance must be ...accompanied by other scalar states for perturbative unitarity in vector-boson scattering to be preserved. The simplest setup consistent with perturbative unitarity and with the data of the diphoton excess is the Georgi-Machacek model. The custodial singlet of the model is responsible for the diphoton excess; it is mainly produced in the diphoton fusion channel, and its loop-induced coupling to the photon pairs is enhanced by the doubly charged scalar with its large (dimensionful) coupling to the custodial singlet.
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