Vacuum Stability and the MSSM Higgs Mass

In the Minimal Supersymmetric Standard Model (MSSM), a Higgs boson mass of 125 GeV can be obtained with moderately heavy scalar top superpartners provided they are highly mixed. The source of this mixing, a soft trilinear stop-stop-Higgs coupling, can result in the appearance of charge- and color-breaking minima in the scalar potential of the theory. If such a vacuum exists and is energetically favorable, the Standard Model-like vacuum can decay to it via quantum tunnelling. In this work we investigate the conditions under which such exotic vacua arise, and we compute the tunnelling rates to them. Our results provide new constraints on the scalar top quarks of the MSSM.Comment: 22 pages, 11 figures. References added. Matches published versio

Electroweakino constraints from LHC data

We investigate the sensitivity of existing LHC searches to the charginos and neutralinos of the MSSM when all the other superpartners are decoupled. In this limit, the underlying parameter space reduces to a simple four-dimensional set $\{M_1,\,M_2,\,\mu,\,\tan\beta\}$. We examine the constraints placed on this parameter space by a broad range of LHC searches taking into account the full set of relevant production and decay channels. We find that the exclusions implied by these searches exceed existing limits from LEP only for smaller values of the Bino mass $M_1 \lesssim 150$ GeV. Our results have implications for MSSM dark matter and electroweak baryogenesis.Comment: 30 pages, 15 figure

The tension between gauge coupling unification, the Higgs boson mass, and a gauge-breaking origin of the supersymmetric mu-term

We investigate the possibility of generating the $\mu$-term in the MSSM by the condensation of a field that is a singlet under the SM gauge group but charged under an additional family-independent $U(1)_X$ gauge symmetry. We attempt to do so while preserving the gauge coupling unification of the MSSM. For this, we find that SM non-singlet exotics must be present in the spectrum. We also prove that the pure $U(1)_X$ anomalies can always be solved with rationally charged fields, but that a large number of SM singlets are often required. For $U(1)_X$ charges that are consistent with an embedding of the MSSM in SU(5) or SO(10), we show that the $U(1)_X$ charges of the MSSM states can always be expressed as a linear combination of abelian subgroups of $E_6$. However, the SM exotics do not appear to have a straightforward embedding into GUT multiplets. We conclude from this study that if this approach to the $\mu$-term is correct, as experiment can probe, it will necessarily complicate the standard picture of supersymmetric grand unification.Comment: 10 pages, no figure

New Limits on Light Hidden Sectors from Fixed-Target Experiments

New physics can be light if it is hidden, coupling very weakly to the Standard Model. In this work we investigate the discovery prospects of Abelian hidden sectors in lower-energy fixed-target and high-precision experiments. We focus on a minimal supersymmetric realization consisting of an Abelian vector multiplet, coupled to hypercharge by kinetic mixing, and a pair of chiral Higgs multiplets. This simple theory can give rise to a broad range of experimental signals, including both commonly-studied patterns of hidden vector decay as well as new and distinctive hidden sector cascades. We find limits from the production of hidden states other than the vector itself. In particular, we show that if the hidden Abelian symmetry is higgsed, and the corresponding hidden Higgs boson has visible decays, it severely restricts the ability of the hidden sector to explain the anomalous muon magnetic moment.Comment: 44 pages + appendices/references, 28 figures. Figures in secs 5 and 7 updated to correct error in hadronic exclusions; limits slightly weaker, but qualitative conclusions unchange

Non-Thermal Dark Matter from Cosmic Strings

Cosmic strings can be created in the early universe during symmetry-breaking phase transitions, such as might arise if the gauge structure of the standard model is extended by additional U(1) factors at high energies. Cosmic strings present in the early universe form a network of long horizon-length segments, as well as a population of closed string loops. The closed loops are unstable against decay, and can be a source of non-thermal particle production. In this work we compute the density of WIMP dark matter formed by the decay of gauge theory cosmic string loops derived from a network of long strings in the scaling regime or under the influence of frictional forces. We find that for symmetry breaking scales larger than 10^10 GeV, this mechanism has the potential to account for the observed relic density of dark matter. For symmetry breaking scales lower than this, the density of dark matter created by loop decays from a scaling string network lies below the observed value. In particular, the cosmic strings originating from a U(1) gauge symmetry broken near the electroweak scale, that could lead to a massive Z' gauge boson observable at the LHC, produce a negligibly small dark matter relic density by this mechanism.Comment: 22 pages, 4 figures, added discussion about boosted decay products from loop cusp

Higgs Boson Decays to Dark Photons through the Vectorized Lepton Portal

Vector-like fermions charged under both the Standard Model and a new dark gauge group arise in many theories of new physics. If these fermions include an electroweak doublet and singlet with equal dark charges, they can potentially connect to the Higgs field through a Yukawa coupling in analogy to the standard neutrino portal. With such a coupling, fermion loops generate exotic decays of the Higgs boson to one or more dark vector bosons. In this work we study a minimal realization of this scenario with an Abelian dark group. We investigate the potential new Higgs decays modes, we compute their rates, and we study the prospects for observing them at the Large Hadron Collider and beyond given the other experimental constraints on the theory. We also discuss extensions of the theory to non-Abelian dark groups.Comment: 32 pages, 5 figures, updated to match JHEP versio