Motivated by searches for 0νββ decay in nuclear experiments and collider probes of lepton number violation at dimension d ≥ 7, we investigate the sensitivity to the d = 5 Weinberg operator using the ...nonresonant signature pp → ℓ±ℓ'± jj at the LHC. We develop a prescription for the operator that is applicable in collisions and decays, and focus on the ℓℓ′ = μμ channel, which is beyond the reach of nuclear decays. For a Wilson coefficient Cμμ5 = 1, scales as heavy as Λ ∼ 8.3 (1) TeV can be probed with L = 300 fb −1 (3 ab−1). This translates to an effective μμ Majorana mass of |mμμ| ∼ 7.3(5.4) GeV and establishes a road map for testing the Weinberg operator at accelerators.
Scenarios for multi-component scalar dark matter based on a single Z$_{N}$ (N ≥ 4) symmetry are simple and well-motivated. In this paper we investigate, for the first time, the phenomenology of the ...Z$_{5}$ model for two-component dark matter. This model, which can be seen as an extension of the well-known singlet scalar model, features two complex scalar fields — the dark matter particles — that are Standard Model singlets but have different charges under a Z$_{5}$ symmetry. The interactions allowed by the Z$_{5}$ give rise to novel processes between the dark matter particles that affect their relic densities and their detection prospects, which we study in detail. The key parameters of the model are identified and its viable regions are characterized by means of random scans. We show that, unlike the singlet scalar model, dark matter masses below the TeV are still compatible with present data. Even though the dark matter density turns out to be dominated by the lighter component, we find that current and future direct detection experiments may be sensitive to signals from both dark matter particles.
We apply the formalism of amplitude symmetries to the angular distribution of the decays B → D$^{∗}$ℓν for ℓ = e, μ, τ . We show that the angular observables used to describe the distribution of this ...class of decays are not independent in absence of New Physics contributing to tensor operators. We derive sets of relations among the angular coefficients of the decay distribution for the massless and massive lepton cases which can be used to probe in a very general way the consistency among the angular observables and the underlying New Physics at work. We use these relations to access the longitudinal polarisation fraction of the D$^{∗}$ using different angular coefficients from the ones used by Belle experiment. This in the near future can provide an alternative strategy to measure $ {F}_L^{D\ast } $ in B → D$^{∗}$τν and to understand the relatively high value measured by the Belle experiment. Using the same symmetries, we identify three observables which may exhibit a tension if the experimental value of $ {F}_L^{D\ast } $ remains high. We discuss how these relations can be exploited for binned measurements. We also propose a new observable that could test for specific scenarios of New Physics generated by light right-handed neutrinos. Finally we study the prospects of testing these relations based on the projected experimental sensitivity of new experiments.
Motivated by a simultaneous explanation of the apparent discrepancies in the light charged lepton anomalous magnetic dipole moments, and the anomalous internal pair creation in $^{8}$Be nuclear ...transitions, we explore a simple New Physics model, based on an extension of the Standard Model gauge group by a U(1)$_{B−L}$. The model further includes heavy vector-like fermion fields, as well as an extra scalar responsible for the low-scale breaking of U(1)$_{B−L}$, which gives rise to a light Z′ boson. The new fields and currents allow to explain the anomalous internal pair creation in $^{8}$Be while being consistent with various experimental constraints. Interestingly, we find that the contributions of the Z′ and the new U(1)$_{B−L}$-breaking scalar can also successfully account for both (g −2)$_{e,μ}$ anomalies; the strong phenomenological constraints on the model’s parameter space ultimately render the combined explanation of (g − 2)$_{e}$ and the anomalous internal pair creation in $^{8}$Be particularly predictive. The underlying idea of this minimal “prototype model” can be readily incorporated into other protophobic U(1) extensions of the Standard Model.
Physics at the e+e- linear collider Moortgat-Pick, G.; Baer, H.; Battaglia, M. ...
The European physical journal. C, Particles and fields,
08/2015, Letnik:
75, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A comprehensive review of physics at an
e
+
e
-
linear collider in the energy range of
s
=
92
GeV–3 TeV is presented in view of recent and expected LHC results, experiments from low-energy as well ...as astroparticle physics. The report focusses in particular on Higgs-boson, top-quark and electroweak precision physics, but also discusses several models of beyond the standard model physics such as supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analysed as well.
Abstract
We revisit the information on the two lightest
$$a_0$$
a
0
resonances and
S
-wave
$$\pi \eta $$
π
η
scattering that can be extracted from photon–photon scattering experiments. For this ...purpose we construct a model for the
S
-wave photon–photon amplitudes which satisfies analyticity properties, two-channel unitarity and obeys the soft photon as well as the soft pion constraints. The underlying I=1 hadronic
T
-matrix involves six phenomenological parameters and is able to account for two resonances below 1.5 GeV. We perform a combined fit of the
$$\gamma \gamma \rightarrow \pi \eta $$
γ
γ
→
π
η
and
$$\gamma \gamma \rightarrow K_SK_S$$
γ
γ
→
K
S
K
S
high statistics experimental data from the Belle collaboration. Minimisation of the
$$\chi ^2$$
χ
2
is found to have two distinct solutions with approximately equal
$$\chi ^2$$
χ
2
. One of these exhibits a light and narrow excited
$$a_0$$
a
0
resonance analogous to the one found in the Belle analysis. This however requires a peculiar coincidence between the
$$J=0$$
J
=
0
and
$$J=2$$
J
=
2
resonance effects which is likely to be unphysical. In both solutions the
$$a_0(980)$$
a
0
(
980
)
resonance appears as a pole on the second Riemann sheet. The location of this pole in the physical solution is determined to be
$$m-i\varGamma /2=1000.7^{+12.9}_{-0.7} -i\,36.6^{+12.7}_{-2.6}$$
m
-
i
Γ
/
2
=
1000
.
7
-
0.7
+
12.9
-
i
36
.
6
-
2.6
+
12.7
MeV. The solutions are also compared to experimental data in the kinematical region of the decay
$$\eta \rightarrow \pi ^0\gamma \gamma $$
η
→
π
0
γ
γ
. In this region an isospin violating contribution associated with
$${\pi ^+}{\pi ^-}$$
π
+
π
-
rescattering must be added for which we provide a dispersive evaluation.
Abstract
In this paper we present a detailed analysis of the contribution of the Light-by-Light (LbL), Durham and double diffractive processes for the diphoton production in ultraperipheral
PbPb
...collisions at the Large Hadron Collider (LHC), High-Energy LHC (HE-LHC) and Future Circular Collider (FCC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity, transverse momentum and acoplanarity distributions are presented. Our results indicate that the contribution of the Durham process is negligible and that the double diffractive process can be strongly suppressed by the exclusivity cuts, which will allow to perform a precise analysis of the LbL scattering, as well the search of beyond Standard Model physics in this final state.
The universal one-loop effective action Drozd, Aleksandra; Ellis, John; Quevillon, Jérémie ...
The journal of high energy physics,
03/2016, Letnik:
2016, Številka:
3
Journal Article
Recenzirano
Odprti dostop
A
bstract
We present the universal one-loop effective action for all operators of dimension up to six obtained by integrating out massive, non-degenerate multiplets. Our general expression may be ...applied to loops of heavy fermions or bosons, and has been checked against partial results available in the literature. The broad applicability of this approach simplifies one-loop matching from an ultraviolet model to a lower-energy effective field theory (EFT), a procedure which is now reduced to the evaluation of a combination of matrices in our universal expression, without any loop integrals to evaluate. We illustrate the relationship of our results to the Standard Model (SM) EFT, using as an example the supersymmetric stop and sbottom squark Lagrangian and extracting from our universal expression the Wilson coefficients of dimension-six operators composed of SM fields.
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