Messenger Mass Research Articles

Messenger inflation in gauge mediation and super-WIMP dark matter

We discuss phenomenological viability of a novel inflationary model in the minimal gauge mediated supersymmetry breaking scenario. In this model, cosmic inflation is realized in the flat direction along the messenger supermultiplets and a natural dark matter candidate is the gravitino from the out-of-equilibrium decay of the binolike neutralino at late times, which is called the super-WIMP scenario. The produced gravitino is warmish and can have a large free-streaming length; thus the cusp anomaly in the small scale structure formation may be mitigated. We show that the requirement of the Standard Model Higgs boson mass to be ${m}_{{h}^{0}}=125.1\text{ }\text{ }\mathrm{GeV}$ gives a relation between the spectrum of the cosmic microwave background and the messenger mass $M$. We find, for the $e$-folding number ${N}_{e}=60$, the Planck 2018 constraints (TT, TE, $\mathrm{EE}+\mathrm{lowE}+\mathrm{lensing}+\mathrm{BK}15+\mathrm{BAO}$, 68% confidence level) give $M>3.64\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{ }\mathrm{GeV}$. The gravitino dark matter mass is ${m}_{3/2}<5.8\text{ }\text{ }\mathrm{GeV}$ and the supersymmetry breaking scale $\mathrm{\ensuremath{\Lambda}}$ is found to be in the range $(1.28--1.33)\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{GeV}$. Future cosmic microwave background observation is expected to give tighter constraints on these parameters.

An explicit calculation of pseudo-goldstino mass at the leading three-loop level

Pseudo-goldstinos appear in the scenario of multi-sector SUSY breaking. Unlike the true goldstino which is massless and absorbed by the gravitino, pseudo-goldstinos could obtain mass from radiative effects. In this note, working in the scenario of two-sector SUSY breaking with gauge mediation, we explicitly calculate the pseudo-goldstino mass at the leading three-loop level and provide the analytical results after performing Taylor expansions in the loop integrals. In our calculation we consider the general case of messenger masses (not necessarily equal) and include the higher order terms of SUSY breaking scales. Our results can reproduce the numerical value estimated previously at the leading order of SUSY breaking scales with the assumption of equal messenger masses. It turns out that the results are very sensitive to the ratio of messenger masses, while the higher order terms of SUSY breaking scales are rather small in magnitude. Depending on the ratio of messenger masses, the pseudo-goldstino mass can be as low as mathcal{O} (0.1) GeV.

Charms of strongly interacting conformal gauge mediation

By extending a previously proposed conformal gauge mediation model, we construct a gauge-mediated SUSY breaking (GMSB) model where a SUSY-breaking scale, a messenger mass, the μ-parameter and the gravitino mass in a minimal supersymmetric (SUSY) Standard Model (MSSM) are all explained by a single mass scale, a R-symmetry breaking scale. We focus on a low scale SUSY-breaking scenario with the gravitino mass m3/2 = mathcal{O}(1)mathrm{eV} , which is free from the cosmological gravitino problem and relaxes the fine-tuning of the cosmological constant. Both the messenger and SUSY-breaking sectors are subject to a hidden strong dynamics with the conformality above the messenger mass threshold (and hence the name of the model “strongly interacting conformal gauge mediation”). In our model, the Higgs B-term is suppressed and a large tan β is predicted, resulting in the relatively light second CP-even Higgs and the CP-odd Higgs with a sizable production cross section. These Higgs bosons can be tested at future LHC experiments.

Metastable supersymmetry breaking in terms of Peccei–Quinn mechanism

Gauge-mediated supersymmetry breaking at metastable vacuum is reconsidered in terms of the Peccei–Quinn (PQ) mechanism. We suggest that for acceptable μ-value generation, such a class of model should involve messenger mass generation via the PQ-breaking process. We then construct a model in context of the Izawa–Yanagida–Intriligator–Thomas superpotential with the aid of the effective Kähler coupling induced by an additional super Yang–Mills sector. Therein, the PQ-charged fundamental singlet plays a crucial role in accommodating a sizable μ-value.

No-go for tree-level R-symmetry breaking

We show that in gauge mediation models with tree-level R-symmetry breaking where supersymmetry and R-symmetries are broken by different fields, the gaugino mass either vanishes at one loop or finds a contribution from loop-level R-symmetry breaking. Thus tree-level R-symmetry breaking for phenomenology is either no-go or redundant in the simplest type of models. Including explicit messenger mass terms in the superpotential with a particular R-charge arrangement is helpful to bypass the no-go theorem, and the resulting gaugino mass is suppressed by the messenger mass scale.

FCNC decays of standard model fermions into a dark photon

We analyze a new class of FCNC processes, the $f \to f^{\prime} \, \bar{\gamma}$ decays of a fermion $f$ into a lighter (same-charge) fermion $f^{\prime}$ plus a {\it massless} neutral vector boson, a {\it dark photon} $\bar{\gamma}$. A massless dark photon does not interact at tree level with observable fields, and the $f \!\to\! f^{\prime} \, \bar{\gamma}$ decay presents a characteristic signature where the final fermion $f^{\prime}$ is balanced by a {\it massless invisible} system. Models recently proposed to explain the exponential spread in the standard-model Yukawa couplings can indeed foresee an extra unbroken {\it dark} $U(1)$ gauge group, and the possibility to couple on-shell dark photons to standard-model fermions via one-loop magnetic-dipole kind of FCNC interactions. The latter are suppressed by the characteristic scale related to the mass of heavy messengers, connecting the standard model particles to the dark sector. We compute the corresponding decay rates for the top, bottom, and charm decays ($t\to c\, \bar{\gamma},u\, \bar{\gamma}$, $\;b\to s\, \bar{\gamma},d\, \bar{\gamma}$, and $c\to u \bar{\gamma}$), and for the charged-lepton decays ($\tau \to \mu\, \bar{\gamma}, e\, \bar{\gamma}$, and $\mu \to e \bar{\gamma}$) in terms of model parameters. We find that large branching ratios for both quark and lepton decays are allowed in case the messenger masses are in the discovery range of the LHC. Implications of these new decay channels at present and future collider experiments are briefly discussed.

A closer look to the sgoldstino interpretation of the diphoton excess

We revisit the sgoldstino interpretation of the diphoton excess in the context of gauge mediation. While the bound on the gluino mass might seem to make the sgoldstino contribution to the diphoton excess unobservable, we show that the interpretation is viable in a thin, near critical region of the parameter space. This regime gives rise to drastic departures from the standard gauge mediation picture. While the fermion messengers lie in the (10-100) TeV range, some scalar messengers are significantly lighter and are responsible for the sgoldstino production and decay. Their effective coupling to the sgoldstino is correspondingly enhanced, and a non-perturbative regime is triggered when light and heavy messenger masses differ by a factor $\sim4\pi$. We also comment on the possible role of an R-axion and on the possibility to decouple the sfermions in this context.

Gravitational rescue of minimal gauge mediation

Gravity mediated supersymmetry breaking becomes comparable to gauge mediated supersymmetry breaking contributions when messenger masses are close to the GUT scale. By suitably arranging the gravity contributions, one can modify the soft supersymmetry breaking sector to generate a large stop mixing parameter and a light Higgs mass of 125 GeV. In this kind of hybrid models, however, the nice features of gauge mediation like flavor conservation, etc. are lost. To preserve the nice features, gravitational contributions should become important for lighter messenger masses and should be important only for certain fields. This is possible when the hidden sector contains multiple (at least two) spurions with hierarchical vacuum expectation values. In this case, the gravitational contributions can be organized to be “just right.” We present a complete model with two spurion hidden sector where the gravitational contribution is from a warped flavor model in a Randall–Sundrum setting. Along the way, we present simple expressions to handle renormalization group equations when supersymmetry is broken by two different sectors at two different scales.

Realising effective theories of tribrid inflation: are there effects from messenger fields?

Tribrid inflation is a variant of supersymmetric hybrid inflation in which the inflaton is a matter field (which can be charged under gauge symmetries) and inflation ends by a GUT-scale phase transition of a waterfall field. These features make tribrid inflation a promising framework for realising inflation with particularly close connections to particle physics. Superpotentials of tribrid inflation involve effective operators suppressed by some cutoff scale, which is often taken as the Planck scale. However, these operators may also be generated by integrating out messenger superfields with masses below the Planck scale, which is in fact quite common in GUT and/or flavour models. The values of the inflaton field during inflation can then lie above this mass scale, which means that for reliably calculating the model predictions one has to go beyond the effective theory description. We therefore discuss realisations of effective theories of tribrid inflation and specify in which cases effects from the messenger fields are expected, and under which conditions they can safely be neglected. In particular, we point out how to construct realisations where, despite the fact that the inflaton field values are above the messenger mass scale, the predictions for the observables are (to a good approximation) identical to the ones calculated in the effective theory treatment where the messenger mass scale is identified with the (apparent) cutoff scale.

New calculations in Dirac gaugino models: operators, expansions, and effects

In this work we calculate important one loop SUSY-breaking parameters in models with Dirac gauginos, which are implied by the existence of heavy messenger fields. We find that these SUSY-breaking effects are all related by a small number of parameters, thus the general theory is tightly predictive. In order to make the most accurate analyses of one loop effects, we introduce calculations using an expansion in SUSY breaking messenger mass, rather than relying on postulating the forms of effective operators. We use this expansion to calculate one loop contributions to gaugino masses, non-holomorphic SM adjoint masses, new A-like and B-like terms, and linear terms. We also test the Higgs potential in such models, and calculate one loop contributions to the Higgs mass in certain limits of R-symmetric models, finding a very large contribution in many regions of the , where Higgs fields couple to standard model adjoint fields.

GUT predictions for quark-lepton Yukawa coupling ratios with messenger masses from non-singlets

We propose new predictions from grand unified theories (GUTs) [applicable to both supersymmetric (SUSY) and non-SUSY models] for the ratios of quark and lepton Yukawa couplings. These new predictions arise from splitting the masses of the messenger fields for the GUT-scale Yukawa operators by Clebsch-Gordan factors from GUT symmetry breaking. This has the effect that these factors enter inversely in the predicted quark-lepton Yukawa coupling ratios, leading to new possible GUT predictions. We systematically construct the new predictions that can be realized in this way in SU(5) GUTs and Pati-Salam unified theories and discuss model building applications.

Gravitino thermal production revisited and a new cosmological scenario of gauge mediation

We present a new scenario of gravitino dark matter which is compatible with the thermal leptogenesis. We confirm by an explicit calculation in supergravity that the relic abundance of thermally produced gravitino becomes insensitive to the reheating temperature once the temperature of the Universe exceeds the mass scale of the messenger fields. In such a situation, the correct baryon to dark matter ratio can be obtained by thermal leptogenesis when the reheating temperature after inflation is high enough. We demonstrate in a concrete model of gauge mediation that the correct abundance of gravitino and baryon asymmetry can be reproduced by considering the late-time entropy production from the decay of the SUSY-breaking pseudo-moduli field. The scenario is realized when the gravitino mass is 100 MeV lesssim m_{3/2} lesssim 1 GeV, and the messenger mass scale is 10^6 GeV lesssim M_{mess} lesssim 10^9 GeV.

Singlet extension of the MSSM for 125 GeV Higgs mass with the least tuning

In order to raise the Higgs mass up to 125 GeV and relieve the fine-tuning associated with the heavy s-top mass in the minimal supersymmetric standard model (MSSM), we propose a new singlet extension of the MSSM. In this scenario, the additional Higgs mass is radiatively generated also in a hidden sector, and the effect is tansmitted to the Higgs through a messenger field. The Higgs mass can be efficiently increased by the parameters of the superpotential as in the extra matter scenario, but free from the constraints on extra colored matter fields by the LHC experiments. As a result, the tuning problem can be remarkably mitigated by taking low enough messenger mass (\sim 300 GeV) and mass parameter scales (\sim 500 GeV).

Stringy hidden valleys

We study gauge theories where quasi-hidden sectors are added to the MSSM for the sake of string consistency conditions which would otherwise not be satisfied. We focus on quiver gauge theories motivated by weakly coupled type II orientifold compactifications. Model independent features in this class include an anomalous U(1)_V symmetry which protects messenger masses and has strong consequences for superpotential couplings, a rich phenomenology of heavy and light Z' bosons, and axionic couplings required for anomaly cancellation via the Green-Schwarz mechanism. We discuss possibilities for dark matter and supersymmetry breaking in light of these generic features. Dark matter is necessarily non-baryonic, though many dark matter candidates have weak interactions. Most models have a U(1)_V Y Y anomaly whose cancellation requires couplings which allow for dark matter annihilation into photons through intermediate axions or anomalous Z' bosons, as in two recently proposed scenarios. There is often an additional non-anomalous U(1) symmetry which can give rise to a Fayet-like model of metastable supersymmetry breaking. Breaking of supersymmetry via SQCD can also be realized and flavor masses are often protected. Natural possibilities for mediation include gauge mediation, Z' mediation, and D-instanton mediation, though it is not possible to realize minimal gauge mediation with messengers added for string consistency.

Affleck-Dine baryogenesis, condensate fragmentation and gravitino dark matter in gauge-mediation with a large messenger mass

We study the conditions for successful Affleck-Dine baryogenesis and the origin of gravitino dark matter in GMSB models. AD baryogenesis in GMSB models is ruled out by neutron star stability unless Q-balls are unstable and decay before nucleosynthesis. Unstable Q-balls can form if the messenger mass scale is larger than the flat-direction field Φ when the condensate fragments. We provide an example based on AD baryogenesis along a d = 6 flat direction for the case where m3/2 ≈ 2GeV, as predicted by gravitino dark matter from Q-ball decay. Using a phenomenological GMSB potential which models the Φ dependence of the SUSY breaking terms, we numerically solve for the evolution of Φ and show that the messenger mass can be sufficiently close to the flat-direction field when the condensate fragments. We compute the corresponding reheating temperature and the baryonic charge of the condensate fragments and show that the charge is large enough to produce late-decaying Q-balls which can be the origin of gravitino dark matter.

Solitonic supersymmetry restoration

Q-balls are a possible feature of any model with a conserved, global U(1) symmetry and no massless, charged scalars. It is shown that for a broad class of models of metastable supersymmetry breaking they are extremely influential on the vacuum lifetime and make seemingly viable vacua catastrophically short lived. A net charge asymmetry is not required as there is often a significant range of parameter space where statistical fluctuations alone are sufficient. This effect is examined for two supersymmetry breaking scenarios. It is found that models of minimal gauge mediation (which necessarily have a messenger number U(1)) undergo a rapid, supersymmetry restoring phase transition unless the messenger mass is greater than 108 GeV. Similarly the ISS model, in the context of direct mediation, quickly decays unless the perturbative superpotential coupling is greater than the Standard Model gauge couplings.

Pure general gauge mediation for early LHC searches

We present benchmark points for Pure General Gauge Mediation (GGM) models specifically optimised for early LHC searches. The pure GGM set-up is as defined in our previous paper arXiv:0910.2674: namely we adopt the minimal set-up in which B_mu is generated only through gauge interactions, and as a result tan beta is a prediction rather than an input. The only input parameters are messenger masses together with two independent scales which generate gaugino and scalar masses. The parameter space favoured by current experimental data includes an interesting region with light gluinos (m_g < 500 GeV and relatively heavy squarks) and a bino-like NLSP where early discovery is likely. We also find interesting regions of parameter space where the NLSP is a stau or stau/neutralino co-NLSP and the squark masses are relatively low. We present benchmark points which are typical for each of these three regions, and give the spectrum, branching ratios, and also the overall 2 -> 2 cross-sections. This data in SLHA format can be found at http://www.ippp.dur.ac.uk/~SUSY

Minimal gaugomaly mediation

Mixed anomaly and gauge mediation (“gaugomaly” mediation) gives a natural solution to the SUSY flavor problem with a conventional LSP dark matter candidate. We present a minimal version of gaugomaly mediation where the messenger masses arise directly from anomaly mediation, automatically generating a messenger scale of order 50 TeV. We also describe a simple relaxation mechanism that gives rise to realistic μ and Bμ terms. B is naturally dominated by the anomaly-mediated contribution from top loops, so the μ-Bμ sector only depends on a single new parameter. In the minimal version of this scenario the full SUSY spectrum is determined by two continuous parameters (the anomaly-and gauge-mediated SUSY breaking masses) and one discrete parameter (the number of messengers). We show that these simple models can give realistic spectra with viable dark matter.

A conformal gauge mediation and dark matter with only one mass parameter

If the supersymmetry (SUSY) is a solution to the hierarchy problem, it is puzzling that any SUSY particle has not been discovered yet. We show that there is a low-scale conformal gauge mediation model which contains all necessary ingredients, i.e. not only a SUSY-breaking dynamics and a gauge mediation mechanism, but also a candidate for the dark matter. The model has only one free mass parameter, that is, the mass for messengers. In this model, the dark matter is provided by a composite particle in the SUSY-breaking sector, and the observed value of the dark matter density uniquely fixes the mass of messengers at the order of 10 2 TeV. Then, the sfermion and gaugino masses are fixed to be of order 10 2 – 10 3 GeV without any arbitrariness, thus the SUSY particles are expected not to be discovered at the Tevatron or LEP, while having a discovery possibility at the LHC.

Holographic gauge mediation via strongly coupled messengers

We consider a relative of semi-direct gauge mediation where the hidden sector exists at large 't Hooft coupling. Such scenarios can be difficult to describe using perturbative field theory methods but may fall into the class of holographic gauge mediation scenarios, meaning that they are amenable to the techniques of gauge/gravity duality. We use a recently found gravity solution to examine one such case where the hidden sector is a cascading gauge theory resulting in a confinement scale not much smaller than the messenger mass. In the original construction of holographic gauge mediation, as in other examples of semi-direct gauge mediation at strong coupling, the primary contributions to visible sector soft terms come from weakly coupled messenger mesons. In contrast to these examples, we describe the dual of a gauge theory where there are significant contributions from scales where the strongly coupled messenger quarks are the effective degrees of freedom. In this regime, the visible sector gaugino mass can be calculated entirely from holography.