Vector-like Masses Research Articles

Closing in on new chiral leptons at the LHC

We study the phenomenological viability of chiral extensions of the Standard Model, with new chiral fermions acquiring their mass through interactions with a single Higgs. We examine constraints from electroweak precision tests, Higgs physics and direct searches at the LHC. Our analysis indicates that purely chiral scenarios are perturbatively excluded by the combination of Higgs coupling measurements and LHC direct searches. However, allowing for a partial contribution from vector-like masses opens up the parameter space and non-decoupled exotic leptons could account for the observed 2σ deviation in h → Zγ. This scenario will be further tested in the high-luminosity phase of the LHC.

Natural top-bottom mass hierarchy in composite Higgs models

We consider composite two-Higgs doublet models based on gauge-Yukawa theories with strongly interacting fermions generating the top-bottom mass hierarchy. The model features a single "universal" Higgs-Yukawa coupling, $ g $, which is identified with the top quark $ g\equiv g_t \sim \mathcal{O}(1) $. The top-bottom mass hierarchy arises by soft breaking of a $ \mathbb{Z}_2 $ symmetry by a condensate of strongly interacting fermions. A mass splitting between vector-like masses of the confined techni-fermions controls this top-bottom mass hierarchy. This mechanism can be present in a variety of models based on vacuum misalignment. For concreteness, we demonstrate it in a composite two-Higgs scheme.

Road map through the desert: unification with vector-like fermions

In light of null results from New Physics searches at the LHC, we look at unification of the gauge couplings as a model-building principle. As a first step, we consider extensions of the Standard Model with vector-like fermions. We present a comprehensive list of spectra that feature fermions in two distinct SU(3)C ×SU(2)L×U(1)Y representations, in which precise gauge coupling unification is achieved. We derive upper and lower limits on vector-like masses from proton decay measurements, running of the strong gauge coupling, heavy stable charged particle searches, and electroweak precision tests. We demonstrate that due to a particular hierarchy among the mass parameters required by the unification condition, complementarity of various experimental strategies allows us to probe many of the successful scenarios up to at least 10 TeV.

Softened Symmetry Breaking in Composite Higgs Models.

We propose a new way of breaking the Goldstone symmetry in composite Higgs models, restoring the global symmetry in the mixings between the elementary and composite fermions by completing the former to full representations of this symmetry. The Goldstone symmetry is in turn broken softly by vectorlike mass terms in the elementary sector only. The resulting softened explicit breaking allows for a light Higgs boson, as found at the LHC, and a heavy top quark, without the need of light top partners around the Goldstone scale f∼TeV≪m_{comp}., which remain elusive at the LHC, while we recover the standard scenario in the limit of infinite vectorlike masses.

Stopping quirks at the LHC

Quirks are exotic particles charged under a new confining gauge group that can give rise to unique collider signatures, depending on their vector-like mass, quantum numbers, and the confinement scale. In this work, we consider the possibility that quirks produced at the LHC lose all of their kinetic energy through ionization loss before escaping the detector, and annihilate at a time when there are no active pp collisions. We recast an existing CMS search for out-of-time decays of R-hadrons to place new limits on quirk parameter space. We propose several simple modifications to the existing out-of-time search strategy that can give these searches sensitivity in regions of quirk parameter space not covered by any existing or proposed search strategy.

Towards realistic SUSY grand unification for extended MSSM models

Low-energy supersymmetric models such as the minimal supersymmetric standard model (MSSM), next-to-minimal supersymmetric standard model (NMSSM), and MSSM with vectorlike fermion are consistent with perturbative unification. While the nonminimal extensions naturally explain Higgs mass and dark matter in the low-energy region, it is unclear how seriously they are constrained in the ultraviolet region. Our study shows the following. First, in the case of embedding the MSSM into SU(5) the fit to standard model fermion masses requires a singlet $S$, which leads to unviable embedding of the NMSSM into SU(5) because such $S$ feeds singlet $N$ a mass of order unification scale as well. Second, a similar result holds in the case of embedding the NMSSM into SO(10), where $S$ is replaced by some Higgs fields responsible for SO(10) breaking. Third, on the contrary, for the embedding of the MSSM with 16-dimensional vectorlike fermions into SO(10), the Higgs field responsible for the vectorlike mass of order tera-electron-volts scale can evade those problems the singlet $N$ encounters because of an intermediate mass scale in the 126-dimensional Higgs field.

A flippon related singlet at the LHC II

We consider the 750 GeV diphoton resonance at the 13 TeV LHC in the ${\cal F}$-$SU(5)$ model with a Standard Model (SM) singlet field which couples to TeV-scale vector-like particles, dubbed $flippons$. This singlet field assumes the role of the 750 GeV resonance, with production via gluon fusion and subsequent decay to a diphoton via the vector-like particle loops. We present a numerical analysis showing that the observed 8 TeV and 13 TeV diphoton production cross-sections can be generated in the model space with realistic electric charges and Yukawa couplings for light vector-like masses. We further discuss the experimental viability of light vector-like masses in a General No-Scale ${\cal F}$-$SU(5)$ model, offering a few benchmark scenarios in this consistent GUT that can satisfy all experimental constraints imposed by the LHC and other essential experiments.

The golden strip of correlated top quark, gaugino, and vector-like mass in no-scale, no-parameter [formula omitted

We systematically establish the hyper-surface within the tanβ, top quark mass mt, universal gaugino mass M1/2, and vector-like mass MV parameter volume which is compatible with the application of the no-scale supergravity boundary conditions, particularly the vanishing of the Higgs bilinear soft term Bμ, near to the Planck mass at the point MF of ultimate F-lipped SU(5) unification. MF is elevated from the penultimate partial unification near the traditional GUT scale at a mass M32 by the inclusion of extra F-theory derived heavy vector-like multiplets. We demonstrate that simultaneous adherence to all current experimental constraints, most importantly contributions to the muon anomalous magnetic moment (g−2)μ, the branching ratio limit on (b→sγ), and the 7-year WMAP relic density measurement, dramatically reduces the allowed solutions to a highly non-trivial “golden strip” with tanβ≃15, mt=173.0–174.4 GeV, M1/2=455–481 GeV, and MV=691–1020 GeV, effectively eliminating all extraneously tunable model parameters. We emphasize that the consonance of the theoretically viable mt range with the experimentally established value is an independently correlated “postdiction”. The predicted range of MV is testable at the Large Hadron Collider (LHC). The partial lifetime for proton decay in the leading (e|μ)+π0 channels falls around 4.6×1034 Y, testable at the future DUSEL and Hyper-Kamiokande facilities.

On the Possible Observation of Mirror Matter

The possibility that mirror matter with masses in the several hundred GeV- TeV range exists is explored. Mirror matter appears quite naturally in many unified models of particle interactions both in GUTs and in strings often in vector-like combinations. Some of these vector-like multiplets could escape acquiring super heavy masses and remain light down to the low energies where they acquire vector-like masses of electroweak size. It is found that a very small mixing of the vector-like multiplets with MSSM matter (specifically with the third generation matter) can produce very large contributions to the magnetic moment of the $\tau$ neutrino by as much as several orders of magnitude putting this moment in the range of accessibility of improved experiment. Further, it is shown that if mirror matter exists it would lead to distinctive signatures at colliders and thus such matter can be explored at the LHC energies with available luminosities.

A universal seesaw mechanism in five dimensions

We show the universal seesaw in the extra dimension setup, where three extra vector-like fields exist in the 5D bulk with heavy masses. We take the framework of the left-right symmetric model. The universal seesaw formula is easily obtained as a replacement of the vector-like mass in 4D case M_i to 2 M_* tan[pi RM_i] (M_*: 5D Planck scale, M_i: vector-like bulk mass, and R: compactification radius). The smallness of Dirac neutrino mass can be naturally explained in the 5D setup. We also show the Majorana neutrino case.

Flipped and unflipped [formula omitted] as type IIA flux vacua

On type IIA orientifolds with flux compactifications in supersymmetric AdS vacua, we for the first time construct SU ( 5 ) models with three anti-symmetric 10 representations and without symmetric 15 representations. We show that all the pairs of the anti-fundamental 5 ¯ and fundamental 5 representations can obtain GUT/string-scale vector-like masses after the additional gauge symmetry breaking via supersymmetry preserving Higgs mechanism. Then we have exact three 5 ¯ , and no other chiral exotic particles that are charged under SU ( 5 ) due to the non-Abelian anomaly free condition. Moreover, we can break the SU ( 5 ) gauge symmetry down to the SM gauge symmetry via D6-brane splitting, and solve the doublet–triplet splitting problem. Assuming that the extra one (or several) pair(s) of Higgs doublets and adjoint particles obtain GUT/string-scale masses via high-dimensional operators, we only have the MSSM in the observable sector below the GUT scale. Then the observed low energy gauge couplings can be generated via RGE running if we choose the suitable grand unified gauge coupling by adjusting the string scale. Furthermore, we construct the first flipped SU ( 5 ) model with exact three 10, and the first flipped SU ( 5 ) model in which all the Yukawa couplings are allowed by the global U ( 1 ) symmetries.