Standard Model Gauge Interactions Research Articles

Thermal effects in freeze-in neutrino dark mater production

We present a detailed study of the production of dark matter in the form of a sterile neutrino via freeze-in from decays of heavy right-handed neutrinos. Our treatment accounts for thermal effects in the effective couplings, generated via neutrino mixing, of the new heavy neutrinos with the Standard Model gauge and Higgs bosons and can be applied to several low-energy fermion seesaw scenarios featuring heavy neutrinos in thermal equilibrium with the primordial plasma. We find that the production of dark matter is not as suppressed as to what is found when considering only Standard Model gauge interactions. Our study shows that the freeze-in dark matter production could be efficient.

Toward a UV model of kinetic mixing and portal matter. III. Relating portal matter and right-handed neutrino masses

The kinetic mixing (KM) of a dark photon (DP) with the familiar one of the Standard Model (SM) requires the existence of a new set of fields, called portal matter (PM), which carry both SM and dark sector quantum numbers, some whose masses may lie at the TeV scale. In the vanilla KM model, the dark gauge group is just the simple $G_{Dark}=U(1)_D$ needed to describe the DP while the SM gauge interactions are described by the usual $G_{SM}=SU(3)_c\times SU(2)_L\times U(1)_Y$. However, we need to go beyond this simple model to gain a better understanding of the interplay between $G_{SM}$ and $G_{Dark}$ and, in particular, determine how they both might fit into a more unified construction. Following our previous analyses, this generally requires $G_{Dark}$ to be extended to a non-abelian group, \eg, $SU(2)_I\times U(1)_{Y_I}$, under which both the PM and SM fields may transform non-trivially. In this paper, also inspired by our earlier work on top-down models, we consider extending the SM gauge group to that of the Left-Right Symmetric Model (LRM) and, in doing so, through common vacuum expectation values, link the mass scales associated with the breaking of $G_{Dark}\to U(1)_D$ and the PM fields to that of the RH-neutrino as well as the heavy gauge bosons of the LRM. This leads to an interesting interplay between the now coupled phenomenologies of both visible and dark sectors at least some of which may be probed at, \eg, the LHC and/or at the future FCC-hh.

Constraining photon portal Dark Matter with TEXONO and COHERENT data

Dark Matter may reside in sector without Standard Model (SM) gauge interactions. One way in which such a dark sector can still impact SM particles through non-gravitational interactions is via the “photon portal” in which a dark photon kinetically mixes with the ordinary SM photon. We study the implications of this setup for electron recoil events at TEXONO reactor and nuclear recoil events at the COHERENT experiment. We find that the recent COHERENT data rules out previously allowed regions of parameter space favored by the thermal relic hypothesis for the DM abundance. When mapped onto the DM-electron cross section, we find that COHERENT provides the leading direct constraints for DM masses < 30 MeV.

Fermionic dark matter in a simple t-channel model

We consider a fermionic dark matter (DM) particle in renormalizable Standard Model (SM) gauge interactions in a simple t-channel model. The DM particle interactions with SM fermions is through the exchange of scalar and vector mediators which carry colour or lepton number. In the case of coloured mediators considered in this study, we find that if the DM is thermally produced and accounts for the observed relic density almost the entire parameter space is ruled out by the direct detection observations. The bounds from the monojet plus missing energy searches at the Large Hadron Collider are less stringent in this case. In contrast for the case of Majorana DM, we obtain strong bounds from the monojet searches which rule out DM particles of mass less than about a few hundred GeV for both the scalar and vector mediators.

A minimal model for SU(N ) vector dark matter

We study an extension of the Standard Model featuring a hidden sector that consists of a new scalar charged under a new SU$(N)_D$ gauge group, singlet under all Standard Model gauge interactions, and coupled with the Standard Model only via a Higgs portal. We assume that the theory is classically conformal, with electroweak symmetry breaking dynamically induced via the Coleman-Weinberg mechanism operating in the hidden sector. Due to the symmetry breaking pattern, the SU$(N)_D$ gauge group is completely Higgsed and the resulting massive vectors of the hidden sector constitute a stable dark matter candidate. We perform a thorough scan over the parameter space of the model at different values of $N=2$, $3$, and $4$, and investigate the phenomenological constraints. We find that $N=2,3$ provide the most appealing model setting in light of present data from colliders and dark matter direct search experiments. We expect a heavy Higgs to be discovered at LHC by the end of Run II or the $N=3$ model to be ruled out.

Decay of the standard model Higgs field after inflation

We study the nonperturbative dynamics of the Standard Model (SM) after inflation, in the regime where the SM is decoupled from (or weakly coupled to) the inflationary sector. We use classical lattice simulations in an expanding box in (3+1) dimensions, modeling the SM gauge interactions with both global and Abelian-Higgs analogue scenarios. We consider different post-inflationary expansion rates. During inflation, the Higgs forms a condensate, which starts oscillating soon after inflation ends. Via nonperturbative effects, the oscillations lead to a fast decay of the Higgs into the SM species, transferring most of the energy into $Z$ and $W^{\pm}$ bosons. All species are initially excited far away from equilibrium, but their interactions lead them into a stationary stage, with exact equipartition among the different energy components. From there on the system eventually reaches equilibrium. We have characterized in detail, in the different expansion histories considered, the evolution of the Higgs and of its dominant decay products, until equipartition is established. We provide a useful mapping between simulations with different parameters, from where we derive a master formula for the Higgs decay time, as a function of the coupling constants, Higgs initial amplitude and postinflationary expansion rate.

Hidden dark matter sector, dark radiation, and the CMB

We consider theories where dark matter is composed of a thermal relic of weak scale mass, whose couplings to the Standard Model (SM) are however too small to give rise to the observed abundance. Instead, the abundance is set by annihilation to light hidden sector states that carry no charges under the SM gauge interactions. In such a scenario the constraints from direct and indirect detection, and from collider searches for dark matter, can easily be satisfied. The masses of such light hidden states can be protected by symmetry if they are Nambu-Goldstone bosons, fermions, or gauge bosons. These states can then contribute to the cosmic energy density as dark radiation, leading to observable signals in the cosmic microwave background (CMB). Furthermore, depending on whether or not the light hidden sector states self-interact, the fraction of the total energy density that free-streams is either decreased or increased, leading to characteristic effects on both the scalar and tensor components of the CMB anisotropy that allows these two cases to be distinguished. The magnitude of these signals depends on the number of light degrees of freedom in the hidden sector, and on the temperature at which it kinetically decouples from the SM. We consider a simple model that realizes this scenario, based on a framework in which the SM and hidden sector are initially in thermal equilibrium through the Higgs portal, and show that the resulting signals are compatible with recent Planck results, while large enough to be detected in upcoming experiments such as CMBPol and CMB Stage-IV. Invisible decays of the Higgs into hidden sector states at colliders can offer a complementary probe of this model.

Low scale unification of gauge interactions

We investigate the possibility to realize the unification of the Standard Model gauge interactions at the low scale in four dimensions. We find that the fields needed to define a minimal theory where baryon and lepton numbers are local symmetries, allow for unification at the low scale in agreement with experiments. In these scenarios the proton is stable and we briefly discuss the implications for cosmology.

Is the Higgs boson associated with Coleman-Weinberg dynamical symmetry breaking?

The Higgs mechanism may be a quantum phenomenon, i.e., a Coleman-Weinberg potential generated by the explicit breaking of scale symmetry in Feynman loops. We review the relationship of scale symmetry and trace anomalies, and we show that the Coleman-Weinberg potential can be defined as the solution to a differential renormalization group equation that follows from the trace of the improved stress tensor. We propose a simple phenomenological model with ``maximal visibility'' at the LHC containing a ``dormant'' Higgs doublet [no VEV, coupled to standard model gauge interactions $SU(2)\ifmmode\times\else\texttimes\fi{}U(1)$] with a mass of $\ensuremath{\sim}380\text{ }\text{ }\mathrm{GeV}$. We discuss the LHC phenomenology and UV challenges of such a model. We also give a schematic model in which new heavy fermions, with masses $\ensuremath{\sim}230\text{ }\text{ }\mathrm{GeV}$, can drive a Coleman-Weinberg potential at two loops. The role of the ``improved stress tensor'' is emphasized, and we propose a nongravitational term, analogous to the $\ensuremath{\theta}$ term in QCD, which generates it from a scalar action.

Exploring a dark sector through the Higgs portal at a lepton collider

We investigate the prospects for detecting a hidden sector at an e+e− collider. The hidden sector is assumed to be composed of invisible particles that carry no charges under the Standard Model gauge interactions, and whose primary interactions with ordinary matter are through the Higgs portal. We consider both the cases when the decays of an on-shell Higgs into a pair of hidden sector particles are kinematically allowed, and the case when such decays are kinematically forbidden. We find that at collider energies below a TeV, the most sensitive channel involves production of an on-shell or off-shell Higgs in association with a Z boson, and the subsequent decay of the Higgs into invisible hidden sector states. Focusing on this channel, we find that with order a thousand inverse fb of data at 250 GeV, the decay branching fraction of an on-shell Higgs to invisible hidden sector states can be constrained to lie below half a percent. The corresponding limits on Higgs portal dark matter will be stronger than the bounds from current and upcoming direct detection experiments in much of parameter space. With the same amount of data at 500 GeV, assuming order one couplings, decays of an off-shell Higgs to hidden sector states with a total mass up to about 200 GeV can also be probed. Both the on-shell and off-shell cases represent a significant improvement in sensitivity when compared to the Large Hadron Collider (LHC).

Terascale remnants of unification and supersymmetry at the Planck scale

We predict new particles at the terascale based on the assumptions that the standard model gauge interactions are unified around the gravitational scale with a big desert and new particles originate from hypermultiplets as remnants of supersymmetry, and propose a theoretical framework, which has predictability, at the terascale and beyond.

Baryogenesis byB−Lgeneration due to superheavy particle decay

We have shown that the $B-L$ generation due to the decay of the thermally produced superheavy fields can explain the Baryon assymmetry in the universe if the superheavy fields are heavier than $10^{13-14}$ GeV. Note that although the superheavy fields have non-vanishing charges under the standard model gauge interactions, the thermally prduced baryon asymmetry is sizable. The $B-L$ violating effective operators induced by integrating the superheavy fields have dimension 7, while the operator in the famous leptogenesis has dimension 5. Therefore, the constraints from the nucleon stability can be easily satisfied.

Quantum leptogenesis I

Thermal leptogenesis explains the observed matter–antimatter asymmetry of the universe in terms of neutrino masses, consistent with neutrino oscillation experiments. We present a full quantum mechanical calculation of the generated lepton asymmetry based on Kadanoff–Baym equations. Origin of the asymmetry is the departure from equilibrium of the statistical propagator of the heavy Majorana neutrino, together with CP violating couplings. The lepton asymmetry is calculated directly in terms of Green’s functions without referring to “number densities”. Compared to Boltzmann and quantum Boltzmann equations, the crucial difference are memory effects, rapid oscillations much faster than the heavy neutrino equilibration time. These oscillations strongly suppress the generated lepton asymmetry, unless the standard model gauge interactions, which cause thermal damping, are properly taken into account. We find that these damping effects essentially compensate the enhancement due to quantum statistical factors, so that finally the conventional Boltzmann equations again provide rather accurate predictions for the lepton asymmetry.

LEPTOGENESIS AND LHC PHYSICS WITH TYPE III SEE-SAW

The See-Saw mechanism provides a nice way to explain why neutrino masses are so much lighter than their charged lepton partners. It also provides a nice way to explain baryon asymmetry in our universe via the leptogenesis mechanism. In this talk we review leptogenesis and LHC physics in a See-Saw model proposed in 1989, now termed the Type III See-Saw model. In this model, SU(2)L triplet leptons are introduced with the neutral particles of the triplets playing the role of See-Saw. The triplet leptons have charged partners with standard model gauge interactions resulting in many new features. The gauge interactions of these particles make it easier for leptognesis with low masses, as low as a TeV is possible. The gauge interactions also make the production and detection of triplet leptons at LHC possible. The See-Saw mechanism and leptogenesis due to Type III See-Saw may be tested at LHC.

Hidden charged dark matter

Can dark matter be stabilized by chargeconservation, just as the electron is in the standard model? Weexamine the possibility that dark matter is hidden, that is, neutralunder all standard model gauge interactions, but charged under anexact {\\rm U}(1) gauge symmetry of the hidden sector. Such candidates arepredicted in WIMPless models, supersymmetric models in which hiddendark matter has the desired thermal relic density for a wide range ofmasses. Hidden charged dark matter has many novel properties notshared by neutral dark matter: (1) bound state formation andSommerfeld-enhanced annihilation after chemical freeze out may reduceits relic density, (2) similar effects greatly enhance dark matterannihilation in protohalos at redshifts of z ∼ 30, (3) Comptonscattering off hidden photons delays kinetic decoupling, suppressingsmall scale structure, and (4) Rutherford scattering makes such darkmatter self-interacting and collisional, potentially impactingproperties of the Bullet Cluster and the observed morphology ofgalactic halos. We analyze all of these effects in a WIMPless modelin which the hidden sector is a simplified version of the minimalsupersymmetric standard model and the dark matter is a hidden sectorstau. We find that charged hidden dark matter is viable andconsistent with the correct relic density for reasonable modelparameters and dark matter masses in the range 1 GeV ≲ mX ≲ 10 TeV. At the same time, in the preferred range of parameters,this model predicts cores in the dark matter halos of small galaxiesand other halo properties that may be within the reach of futureobservations. These models therefore provide a viable andwell-motivated framework for collisional dark matter with Sommerfeldenhancement, with novel implications for astrophysics and dark mattersearches.

Thermal relics in hidden sectors

Dark matter may be hidden, with no standard model gauge interactions. At the same time,in WIMPless models (WIMP: weakly interacting massive particles) with hiddenmatter masses proportional to hidden gauge couplings squared, the hidden darkmatter’s thermal relic density may naturally be in the right range, preservingthe key quantitative virtue of WIMPs. We consider this possibility in detail. Wefirst determine model-independent constraints on hidden sectors from big bangnucleosynthesis and the cosmic microwave background. Contrary to conventionalwisdom, large hidden sectors are easily accommodated. A flavour-free version ofthe standard model is allowed if the hidden sector is just 30% colder than theobservable sector after reheating. Alternatively, if the hidden sector contains aone-generation version of the standard model with characteristic mass scale below1 MeV, even identical reheating temperatures are allowed. We then analyse hiddensector freeze-out in detail for a concrete model, solving the Boltzmann equationnumerically and explaining the results from both observable and hidden sector points ofview. We find that WIMPless dark matter does indeed obtain the correct relicdensity for masses in the range . The upper bound results from the requirement of perturbativity, and the lower boundassumes that the observable and hidden sectors reheat to the same temperature, and israised to the MeV scale if the hidden sector is ten times colder. WIMPless dark mattertherefore generalizes the WIMP paradigm to the largest mass range possible for viablethermal relics and provides a unified framework for exploring dark matter signals acrossnine orders of magnitude in dark matter mass.

Unification of gauge symmetries in theories with dynamical symmetry breaking

We analyze approaches to the partial or complete unification of gauge symmetries in theories with dynamical symmetry breaking. Several types of models are considered, including those that (i) involve sufficient unification to quantize electric charge, (ii) attempt to unify the three standard-model gauge interactions in a simple Lie group that forms a direct product with an extended technicolor group, and, most ambitiously, (iii) attempt to unify the standard-model gauge interactions with (extended) technicolor in a simple Lie group.

A minimally fine-tuned supersymmetric standard model

We construct supersymmetric theories in which the correct scale for electroweak symmetry breaking is obtained without significant fine-tuning. We calculate the fine-tuning parameter for these theories to be at the 20% level, which is significantly better than in conventional supersymmetry breaking scenarios. Supersymmetry breaking occurs at a low scale of order 100 TeV, and is transmitted to the supersymmetric standard-model sector through standard-model gauge interactions. The Higgs sector contains two Higgs doublets and a singlet field, with a superpotential that takes the most general form allowed by gauge invariance. An explicit model is constructed in 5D warped space with supersymmetry broken on the infrared brane. We perform a detailed analysis of electroweak symmetry breaking for this model, and demonstrate that the fine-tuning is in fact reduced. A new candidate for dark matter is also proposed, which arises from the extended Higgs sector of the model. Finally, we discuss a purely 4D theory which may also significantly reduce fine-tuning.

Supersymmetric fine-tuning problem and TeV-scale exotic scalars

A general framework is presented for supersymmetric theories that do not suffer from fine-tuning in electroweak symmetry breaking. Supersymmetry is dynamically broken at a scale $\ensuremath{\Lambda}\ensuremath{\approx}(10--100)\text{ }\text{ }\mathrm{TeV}$, which is transmitted to the supersymmetric standard model sector through standard model gauge interactions. The dynamical supersymmetry-breaking sector possesses an approximate global $SU(5)$ symmetry, whose $SU(3)\ifmmode\times\else\texttimes\fi{}SU(2)\ifmmode\times\else\texttimes\fi{}U(1)$ subgroup is explicitly gauged and identified as the standard model gauge group. This $SU(5)$ symmetry is dynamically broken at the scale $\ensuremath{\Lambda}$, leading to pseudo-Goldstone boson states, which we call xyons. We perform a detailed estimate for the xyon mass and find that it is naturally in the multi-TeV region. We study general properties of xyons, including their lifetime, and study their collider signatures. A generic signature is highly ionizing tracks caused by stable charged bound states of xyons, which may be observed at the CERN LHC. We also consider cosmology in our scenario and find that a consistent picture can be obtained. Our framework is general and does not depend on the detailed structure of the Higgs sector, nor on the mechanism of gaugino-mass generation.

Test of gauge-Yukawa unification

Recently it has been proposed that, in the framework of quantum field theory, both the Standard Model gauge and Yukawa interactions arise from a single gauge interaction in higher dimensions with supersymmetry. This leads to the unification of the Standard Model gauge couplings and the third family Yukawa couplings at the GUT scale. In this Letter, we make a detailed study of this unification using the current experimental data, and find a good agreement in a significant region of the parameter space. Similar relations, required in finite grand unification models, are also studied.