A Portalino to the Dark Sector

"Portal" models that connect the Standard Model to a Dark Sector allow for a wide variety of scenarios beyond the simplest WIMP models. Kinetic mixing of gauge fields in particular has allowed a broad range of new ideas. However, the models that evade CMB constraints are often non-generic, with new mass scales and operators to split states and suppress indirect detection signals. Models with a "portalino", a neutral fermion that marries a linear combination of a standard model neutrino and dark sector fermion and carries a conserved quantum number, can be simpler. This is especially interesting for interacting dark sectors; then the unmarried linear combination which we identify as the standard model neutrino inherits these interactions too, and provides a new, effective interaction between the dark sector and the standard model. These interactions can be simple $Z'$ type interactions or lepton-flavor changing. Dark matter freezes out into neutrinos, thereby evading CMB constraints, and conventional direct detection signals are largely absent. The model offers different signals, however. The "portalino" mechanism itself predicts small corrections to the standard model neutrino couplings as well as the possibility of discovering the portalino particle in collider experiments. Possible cosmological and astroparticle signatures include monochromatic neutrino signals from annihilation, spectral features in high energy CR neutrinos as well as conventional signals of additional light species and dark matter interactions.Comment: v2 - minor changes, references adde

Naturally heavy superpartners and a Little Higgs

We construct an extension of the MSSM in which scalar superpartners can naturally be as heavy as 1 TeV. In the MSSM, the most significant fine tuning stems from the logarithmically enhanced top-stop loop contribution to the soft Higgs mass. We combine supersymmetry with the "simplest little Higgs" to render this loop finite, thereby removing the large logarithm even in models in which superpartner masses are generated at high scales such as in supergravity. Our model predicts an extended Higgs sector, superpartner masses near a TeV and little Higgs partners at a few TeV.Comment: 18 pages, 1 figur

Explaining the t-tbar asymmetry with a light axigluon

We propose an axigluon with mass between 400 and 450 GeV and flavor universal couplings to quarks to explain the Tevatron t-tbar forward-backward asymmetry. The model predicts a small negative asymmetry for t-tbar pairs with invariant mass below 450 GeV and a large positive asymmetry above 450 GeV. The asymmetry arises from interference between s-channel gluon and axigluon diagrams and requires a relatively weakly coupled axigluon ($g_{a} = g_{qcd}/3$). Axigluon-gluon interference does not contribute to the t-tbar cross section. New contributions to the cross section arise only at fourth order in the axigluon coupling and are very small for a sufficiently broad axigluon. Dijet measurements do not significantly constrain the axigluon couplings. We propose several possible UV completions of the phenomenological axigluon which explain the required small couplings and large width. Such UV completions necessarily contain new colored fermions or scalars below the axigluon mass and predict multi-jet events with large cross sections at the Tevatron and LHC.Comment: references adde

A hidden solution to the mu/B_mu problem in gauge mediation

We propose a solution to the mu/B_mu problem in gauge mediation. The novel feature of our solution is that it uses dynamics of the hidden sector, which is often present in models with dynamical supersymmetry breaking. We give an explicit example model of gauge mediation where a very simple messenger sector generates both mu and B_mu at one loop. The usual problem, that B_mu is then too large, is solved by strong renormalization effects from the hidden sector which suppress B_mu relative to mu. Our mechanism relies on an assumption about the signs of certain incalculable anomalous dimensions in the hidden sector. Making these assumptions not only allows us to solve the mu/B_mu problem but also leads to a characteristic superpartner spectrum which would be a smoking gun signal for our mechanism.Comment: minor clarifications, examples added, version to appear in PR

The Leptoquark Hunter's Guide: Large Coupling

Leptoquarks have recently received much attention especially because they may provide an explanation to the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies in rare $B$ meson decays. In a previous paper we proposed a systematic search strategy for all possible leptoquark flavors by focusing on leptoquark pair production. In this paper, we extend this strategy to large (order unity) leptoquark couplings which offer new search opportunities: single leptoquark production and $t$-channel leptoquark exchange with dilepton final states. We discuss the unique features of the different search channels and show that they cover complementary regions of parameter space. We collect and update all currently available bounds for the different flavor final states from LHC searches and from atomic parity violation measurements. As an application of our analysis, we find that current limits do not exclude the leptoquark explanation of the $B$ physics anomalies but that the high luminosity run of the LHC will reach the most interesting parameter space.Comment: 33 pages + references, 15 figures, 9 tables, v2: references adde

The Bestest Little Higgs

While little Higgs models provide an interesting way to address the hierarchy problem, concrete models in the literature typically face two major obstacles. First, the mechanism for generating a Higgs quartic coupling often leads to large violations of custodial symmetry. Second, there is a tension between precision electroweak observables in the gauge sector and fine-tuning in the top sector. In this work, we present a new little Higgs model which solves both of these problems. The model is based on an SO(6)xSO(6)/SO(6) coset space which has custodial symmetry built in. The Higgs quartic coupling takes a particularly simple form and does not suffer from the "dangerous singlet" pathology. We introduce a gauge breaking module which decouples the mass of gauge partners from the mass of top partners, allowing for natural electroweak symmetry breaking. The collider phenomenology is dominated by production and decay of the top partners, which are considerably lighter than in traditional little Higgs theories.Comment: 40 pages, 7 figure

Phenomenology of SUSY with scalar sequestering

The defining feature of scalar sequestering is that the MSSM squark and slepton masses as well as all entries of the scalar Higgs mass matrix vanish at some high scale. This ultraviolet boundary condition - scalar masses vanish while gaugino and Higgsino masses are unsuppressed - is independent of the supersymmetry breaking mediation mechanism. It is the result of renormalization group scaling from approximately conformal strong dynamics in the hidden sector. We review the mechanism of scalar sequestering and prove that the same dynamics which suppresses scalar soft masses and the B_mu term also drives the Higgs soft masses to -|mu|^2. Thus the supersymmetric contribution to the Higgs mass matrix from the mu-term is exactly canceled by the soft masses. Scalar sequestering has two tell-tale predictions for the superpartner spectrum in addition to the usual gaugino mediation predictions: Higgsinos are much heavier (mu > TeV) than scalar Higgses (m_A ~ few hundred GeV), and third generation scalar masses are enhanced because of new positive contributions from Higgs loops.Comment: 16 pages and 3 figure

The Leptoquark Hunter's Guide: Pair Production

Leptoquarks occur in many new physics scenarios and could be the next big discovery at the LHC. The purpose of this paper is to point out that a model-independent search strategy covering all possible leptoquarks is possible and has not yet been fully exploited. To be systematic we organize the possible leptoquark final states according to a leptoquark matrix with entries corresponding to nine experimentally distinguishable leptoquark decays: any of {light-jet, b-jet, top} with any of {neutrino, $e/\mu$, $\tau$}. The 9 possibilities can be explored in a largely model-independent fashion with pair-production of leptoquarks at the LHC. We review the status of experimental searches for the 9 components of the leptoquark matrix, pointing out which 3 have not been adequately covered. We plead that experimenters publish bounds on leptoquark cross sections as functions of mass for as wide a range of leptoquark masses as possible. Such bounds are essential for reliable recasts to general leptoquark models. To demonstrate the utility of the leptoquark matrix approach we collect and summarize searches with the same final states as leptoquark pair production and use them to derive bounds on a complete set of Minimal Leptoquark models which span all possible flavor and gauge representations for scalar and vector leptoquarks.Comment: 19 pages + references and appendices, 18 figures, 15 tables. Added references, fixed typo