2,456 research outputs found

### $\tau$-Flavour Violation at the LHC

We study the conditions required for $\chi_2 \to \chi + \tau^\pm \mu^\mp$
decays to yield observable tau flavour violation at the LHC, for cosmologically
interesting values of the neutralino relic density. These condition can be
achieved in the framework of a SU(5) model with a see-saw mechanism that allows
a possible coexistence of a LHC signal a low prediction for radiative LFV
decays.Comment: 7 pages, 5 figures, Prepared for the proceedings of the workshop:
"LC09: $e^+ e^-$ Physics at the TeV Scale and the Dark Matter Connection",
21-24 September 2009, Perugia, Ital

### Exotic coloured fermions and lepton number violation at the LHC

Majorana neutrino mass models with a scale of lepton number violation (LNV)
of order TeV potentially lead to signals at the LHC. Here, we consider an
extension of the standard model with a coloured octet fermion and a scalar
leptoquark. This model generates neutrino masses at 2-loop order. We make a
detailed MonteCarlo study of the LNV signal at the LHC in this model, including
a simulation of standard model backgrounds. Our forecast predicts that the LHC
with 300/fb should be able to probe this model up to colour octet fermion
masses in the range of (2.6-2.7) TeV, depending on the lepton flavour of the
final state.Comment: 14 pages, 2 figure

### Lepton Flavor Violating Photoleptonic Effect

We study lepton flavor violating analogs of the photoelectric effect, with a
final $\mu$ or $\tau$ instead of an electron: $\gamma e\to \mu$ and $\gamma
e\to \tau$. On the basis of the general parametrization of the matrix element
of the electromagnetic current we estimate the upper limits for the cross
sections and event rates of these processes, imposed by the current
experimental bounds on $\mu\to e \gamma$ and $\tau\to e \gamma$ decays.Comment: 6 pages, 1 figure, RevTeX

### Search for Tau Flavour Violation at the LHC

We explore the prospects for searches at the LHC for sparticle decays that
violate $\tau$ lepton number, in the light of neutrino oscillation data and the
seesaw model for neutrino masses and mixing. We analyse the theoretical and
phenomenological conditions required for tau flavour violation to be observable
in \chi_2 \to \chi + \tau^\pm \mu^\mp decays, for cosmologically interesting
values of the relic neutralino LSP density. We study the relevant
supersymmetric parameter space in the context of the Constrained Minimal
Supersymmetric Extension of the Standard Model (CMSSM) and in SU(5) extensions
of the theory. We pay particular attention to the possible signals from
hadronic tau decays, that we analyse using PYTHIA event simulation. We find
that a signal for \tau flavour-violating \chi_2 decays may be observable if the
branching ratio exceeds about 10%. This may be compatible with the existing
upper limit on \tau \to \mu \gamma decays if there is mixing between
right-handed sleptons, as could be induced in non-minimal SU(5) GUTs.Comment: 24 pages, 10 fig

### Dark Matter in SuperGUT Unification Models

After a brief update on the prospects for dark matter in the constrained
version of the MSSM (CMSSM) and its differences with models based on minimal
supergravity (mSUGRA), I will consider the effects of unifying the
supersymmetry-breaking parameters at a scale above M_{GUT}. One of the
consequences of superGUT unification, is the ability to take vanishing scalar
masses at the unification scale with a neutralino LSP dark matter candidate.
This allows one to resurrect no-scale supergravity as a viable phenomenological
model.Comment: 12 pages, 16 figures, To be published in the Proceedings of the 6th
DSU Conference, Leon, Mexico, ed. D. Delepin

### Slepton mass-splittings as a signal of LFV at the LHC

Precise measurements of slepton mass-splittings might represent a powerful
tool to probe supersymmetric (SUSY) lepton flavour violation (LFV) at the LHC.
We point out that mass-splittings of the first two generations of sleptons are
especially sensitive to LFV effects involving $\tau-\mu$ transitions. If these
mass-splittings are LFV induced, high-energy LFV processes like the neutralino
decay {\nt}_2\to\nt_1\tau^{\pm}\mu^{\mp} as well as low-energy LFV processes
like $\tau\to\mu\gamma$ are unavoidable. We show that precise slepton
mass-splitting measurements and LFV processes both at the high- and low-energy
scales are highly complementary in the attempt to (partially) reconstruct the
flavour sector of the SUSY model at work. The present study represents another
proof of the synergy and interplay existing between the LHC, i.e. the {\em
high-energy frontier}, and high-precision low-energy experiments, i.e. the {\em
high-intensity frontier}.Comment: 11 pages, 5 figures. v2: added discussion on backgrounds, added
references, version to be published on JHE

### Neutrino Mass, Sneutrino Dark Matter and Signals of Lepton Flavor Violation in the MRSSM

We study the phenomenology of mixed-sneutrino dark matter in the Minimal
R-Symmetric Supersymmetric Standard Model (MRSSM). Mixed sneutrinos fit
naturally within the MRSSM, as the smallness (or absence) of neutrino Yukawa
couplings singles out sneutrino A-terms as the only ones not automatically
forbidden by R-symmetry. We perform a study of randomly generated sneutrino
mass matrices and find that (i) the measured value of $\Omega_{DM}$ is well
within the range of typical values obtained for the relic abundance of the
lightest sneutrino, (ii) with small lepton-number-violating mass terms
$m_{nn}^{2} {\tilde n} {\tilde n}$ for the right-handed sneutrinos, random
matrices satisfying the $\Omega_{DM}$ constraint have a decent probability of
satisfying direct detection constraints, and much of the remaining parameter
space will be probed by upcoming experiments, (iii) the $m_{nn}^{2} {\tilde n}
{\tilde n}$ terms radiatively generate appropriately small Majorana neutrino
masses, with neutrino oscillation data favoring a mostly sterile lightest
sneutrino with a dominantly mu/tau-flavored active component, and (iv) a
sneutrino LSP with a significant mu component can lead to striking signals of
e-mu flavor violation in dilepton invariant-mass distributions at the LHC.Comment: Revised collider analysis in Sec. 5 after fixing error in particle
spectrum, References adde

### Interplay of LFV and slepton mass splittings at the LHC as a probe of the SUSY seesaw

We study the impact of a type-I SUSY seesaw concerning lepton flavour
violation (LFV) both at low-energies and at the LHC. The study of the di-lepton
invariant mass distribution at the LHC allows to reconstruct some of the masses
of the different sparticles involved in a decay chain. In particular, the
combination with other observables renders feasible the reconstruction of the
masses of the intermediate sleptons involved in $\chi_2^0\to \tilde \ell
\,\ell \to \ell \,\ell\,\chi_1^0$ decays. Slepton mass splittings can be either
interpreted as a signal of non-universality in the SUSY soft breaking-terms
(signalling a deviation from constrained scenarios as the cMSSM) or as being
due to the violation of lepton flavour. In the latter case, in addition to
these high-energy processes, one expects further low-energy manifestations of
LFV such as radiative and three-body lepton decays. Under the assumption of a
type-I seesaw as the source of neutrino masses and mixings, all these LFV
observables are related. Working in the framework of the cMSSM extended by
three right-handed neutrino superfields, we conduct a systematic analysis
addressing the simultaneous implications of the SUSY seesaw for both high- and
low-energy lepton flavour violation. We discuss how the confrontation of
slepton mass splittings as observed at the LHC and low-energy LFV observables
may provide important information about the underlying mechanism of LFV.Comment: 50 pages, 42 eps Figures, typos correcte

### LHC and lepton flavour violation phenomenology of a left-right extension of the MSSM

We study the phenomenology of a supersymmetric left-right model, assuming
minimal supergravity boundary conditions. Both left-right and (B-L) symmetries
are broken at an energy scale close to, but significantly below the GUT scale.
Neutrino data is explained via a seesaw mechanism. We calculate the RGEs for
superpotential and soft parameters complete at 2-loop order. At low energies
lepton flavour violation (LFV) and small, but potentially measurable mass
splittings in the charged scalar lepton sector appear, due to the RGE running.
Different from the supersymmetric 'pure seesaw' models, both, LFV and slepton
mass splittings, occur not only in the left- but also in the right slepton
sector. Especially, ratios of LFV slepton decays, such as Br(${\tilde\tau}_R
\to \mu \chi^0_1$)/Br(${\tilde\tau}_L \to \mu \chi^0_1$) are sensitive to the
ratio of (B-L) and left-right symmetry breaking scales. Also the model predicts
a polarization asymmetry of the outgoing positrons in the decay $\mu^+ \to e^+
\gamma$, A ~ [0,1], which differs from the pure seesaw 'prediction' A=1$.
Observation of any of these signals allows to distinguish this model from any
of the three standard, pure (mSugra) seesaw setups.Comment: 43 pages, 17 figure

- …