Portal Matter and Dark Sector Phenomenology at Colliders

Abstract

If dark matter (DM) interacts with the Standard Model (SM) via the kinetic mixing (KM) portal, it necessitates the existence of massive, likely > ∼ 1 TeV, enabler portal matter (PM) particles that carry both dark and SM quantum numbers which will appear in vacuum polarization-like loop graphs. Such heavy states are only directly accessible at high energy colliders and apparently lie at mass scales beyond the direct kinematic reach of the ILC, CEPC and FCC-ee. A likely possibility is that these new particles are part of the 'next step' toward a UV-complete scenario describing both the SM and dark sector physics. A simple and straightforward example of such a scenario involving a non-abelian dark sector gauge group is employed in this work to demonstrate some of the range expected from this new physics. Here we present a broad survey of existing analyses designed to explore the nature of such PM states in a array of collider contexts, particularly at the LHC, and point out some of the future directions where additional work is obviously required in the hunt for new signatures as well as in model building directions.

Kinetic Mixing, Dark Higgs Triplets, $M_W$ and All That

“…In the most commonly discussed PM models, KM occurs at the 1-loop level in an abelian manner between the SM U (1) Y hypercharge gauge boson and the U (1) D DP via a set of states having both Y, Q D = 0. Such KM mixing is finite and, in principle, calculable in a class of models wherein the condition i Y i Q Di = 0 is satisfied, as was the case in our earlier works [11,12,[14][15][16][17][18]. In the present setup, the presence of the dark scalar triplet with a non-zero vev will also allow for non-abelian KM to occur between the DP and the neutral W 3 , SU (2) L field as the triplet itself carries both weak isospin as well as Q D = 0 and, in fact, alone satisfies the corresponding analogous condition i T 3i Q Di = 0 with T 3 being the third, diagonal SU (2) L generator.…”

“…We also see that, e.g., if z is less than 0.25, then Σ will lie (if g D = e) below 10 −4 and that other KM sources will then likely be needed for a DP in the mass range of interest here so that the range of this parameter is then somewhat restricted. Of course, as previously noted, in a more UV-complete framework beyond the current setup, other new fields, e.g., in the form of Q D = 0 heavy vector-like fermions [11][12][13][14][15][16][17][18], are also potentially present, carrying non-zero values the SM hypercharge so that additional contributions to KM from this more 'conventional' abelian source are obtainable. Here, for simplicity, we will ignore this possibility assuming the Σ is the only source of KM.…”

“…Of particular interest is the kinetic mixing (KM)/vector portal scenario [8,9] where a new gauge field, the dark photon (DP) [10], which is the gauge boson associated with a new U (1) D symmetry, couples to only DM and other dark sector fields. This new gauge field, V , can experience KM with the neutral SM gauge fields via a set of vacuum polarization-like diagrams wherein are exchanged new scalar and/or fermion fields, here termed Portal Matter (PM) [11][12][13][14][15][16][17][18], which carry both dark and SM quantum numbers. Being loop suppressed, the resulting strength of this interaction is rather weak and is usually described via a single parameter, ∼ 10 −4 − 10 −3 , which, for DM and DP in the mass range < ∼ 1 GeV can reproduce the observed DM relic abundance [19] via the conventional freeze-out mechanism while simultaneously avoiding numerous other existing experimental constraints.…”

“…Of course such new fields, e.g., heavy vector-like fermions with both SM and dark sector quantum numbers[11][12][13][14][15][16][17][18], might also be present in a more complete version of the present setup and they would also contribute to abelian KM as usual.…”

Kinetic Mixing from Kaluza-Klein Modes: A Simple Construction for Portal Matter

“…Perhaps the most obvious channel, portal matter pair production from either QCD (in the case of color-triplet portal matter) or electroweak interactions (for leptonic portal matter), has been well-explored in the perfectly analogous scenarios of [19-21, 57, 58], and summarized well in [59], so we see no need to perform the analysis again here-we shall simply quote some results and comment on their relevance in our context. In both the leptonic and quark-like portal matter cases, the pair production cross sections scale quite strongly with the portal matter mass [19,57], so for pair production searches we are especially concerned with the very lightest portal matter states that are present, even in the event of a large ensemble of portal matter states in the model, as long as there are O(1) differences in brane-localized kinetic terms (and hence masses O(1) proportional differences in masses) between portal matter states.…”