Mu2e Conceptual Design Report

Abstract:We study renormalizable extensions of the standard model that contain vectorlike fermions in a (single) complex representation of the standard model gauge group. There are 11 models where the vector-like fermions Yukawa couple to the standard model fermions via the Higgs field. These models do not introduce additional fine-tunings. They can lead to, and are constrained by, a number of different flavor-changing processes involving leptons and quarks, as well as direct searches. An interesting feature of the models with strongly interacting vector-like fermions is that constraints from neutral meson mixings (apart from CP violation in K 0 −K 0 mixing) are not sensitive to higher scales than other flavor-changing neutral-current processes. We identify order 1/(4πM ) 2 (where M is the vector-like fermion mass) one-loop contributions to the coefficients of the four-quark operators for meson mixing, that are not suppressed by standard model quark masses and/or mixing angles.

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“…Future experiments will have a dramatically improved sensitivity to a branching ratio Br(µ → e conv. in Al) ∼ 10 −16 [22,23].…”

Section: Leptonic Modelsmentioning

confidence: 99%

New vector-like fermions and flavor physics

Ishiwata

Ligeti

Wise

2015

J. High Energ. Phys.

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“…However, as only the product of these two couplings is constrained, either of the couplings can be as large as the bound obtained from Z pole observables in the previous section, as long as the other coupling is strongly suppressed. The expected sensitivity of the Mu2e experiment to µ → e conversion in Al, BR(µ → e in Al) 6 × 10 −17 [74], will probe large regions of the presently allowed parameter space.…”

Section: Lepton Flavor Violationmentioning

confidence: 99%

Exotic leptons: Higgs, flavor and collider phenomenology

Altmannshofer

Bauer

Carena

2014

J. High Energ. Phys.

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We study extensions of the standard model by one generation of vector-like leptons with non-standard hypercharges, which allow for a sizable modification of the h → γγ decay rate for new lepton masses in the 300 GeV-1 TeV range. We analyze vacuum stability implications for different hypercharges. Effects in h → Zγ are typically much smaller than in h → γγ, but distinct among the considered hypercharge assignments. Nonstandard hypercharges constrain or entirely forbid possible mixing operators with standard model leptons. As a consequence, the leading contributions to the experimentally strongly constrained electric dipole moments of standard model fermions are only generated at the two loop level by the new CP violating sources of the considered setups. We derive the bounds from dipole moments, electro-weak precision observables and lepton flavor violating processes, and discuss their implications. Finally, we examine the production and decay channels of the vector-like leptons at the LHC, and find that signatures with multiple light leptons or taus are already probing interesting regions of parameter space.

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“…This result will be improved in the near future by 4 orders of magnitudes by the µ → e conversion experiments Mu2e [18] and COMET [19]. Thus, under the reasonable assumption of not having a large hierarchy between the muon and electron couplings, LFV provides the best prospects to probe the framework in the near future.…”

Section: Jhep07(2017)047mentioning

confidence: 99%

A clockwork WIMP

Hambye

Teresi

Tytgat

2017

J. High Energ. Phys.

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We embed a thermal dark matter (DM) candidate within the clockwork framework. This mechanism allows to stabilize the DM particle over cosmological time because it suppresses its decay into Standard Model (SM) particles. At the same time, pair annihilations are unsuppressed, so that the relic density is set by the usual freeze-out of the DM particle from the thermal bath. The slow decay of the DM candidate is induced by "clockwork" particles that can be quite light (rather than at some GUT or Planck scale) and could be searched for at current or future colliders. According to the scenario considered, the very same particles also mediate the annihilation process, thus providing a connection between DM annihilation and DM decay, and fixing the mass scale of the clockwork states, otherwise unconstrained, to be in the TeV range or lighter. We then show how this setup can minimally emerge from the deconstruction of an extra dimension in flat spacetime. Finally, we argue that the clockwork mechanism that we consider could induce Majorana neutrino masses, with a seesaw scale of order TeV or less and Yukawa couplings of order unity.

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Mu2e Conceptual Design Report

Cited by 91 publications

References 9 publications

New vector-like fermions and flavor physics

New vector-like fermions and flavor physics

Exotic leptons: Higgs, flavor and collider phenomenology

A clockwork WIMP

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