35 research outputs found
Gauged U(1) extension of the standard model and phenomenology
No full textElectronic Thesis or DissertationDespite the tremendous success of the Standard Model (SM), it needs to be extended to explain the origin of cosmological inflation, dark matter (DM) and neutrino masses. We consider gauged U(1)x extended SM, where in addition to the SM particles, the model includes a U(1)x scalar, Z' gauge boson, and three generations of right-handed neutrinos (RHNs), where the U(1)x charges of all the particles are defined by a single free parameter xH. In this model context, we discuss the complementarity between the cosmological inflation, the DM physics, and new physics searches at the Large Hadron Colliders (LHC). With the identification of the U(1)x scalar as an inflaton field, we consider the cosmological inflation scenario. For an effective inflaton potential to develop an inflection-point with predictions consistent with cosmological observations, the mass ratios among the Z' boson, the RHNs, and the inflaton are fixed. Requiring the inflationary prediction to be consistent with the current cosmological observation and collider experimental results, we show that our scenario can be tested at the future collider experiments such as the High Luminosity-LHC and the SHiP experiment. We also consider SU(5) x U(1)x scenario, where the SU(5) grand unification of the SM quarks and leptons is realized for xH = -4/5. Hence, the U(1)x charge is quantized in this scenario. With an additional global Z-2 symmetry, one RHN, which is Z-2 odd particles, serves as the DM in the universe. We investigate the Z'-portal RHN DM scenario and find that the constraints from the DM relic abundance and the search results for a Z' boson resonance at the LHC Run-2 are complementary to narrow down the allowed parameter region, which will be fully covered by the future LHC experiments for the Z’ boson mass less than 5 TeV
Inflection-point <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi><mml:mo>−</mml:mo><mml:mi>L</mml:mi></mml:math> Higgs inflation
No full textInflection-point inflation is an interesting possibility to realize a successful slow-roll inflation when inflation is driven by a single scalar field with its initial value below the Planck mass (phi(1) less than or similar to M-P1). In order for a renormalization group (RG) improved effective lambda phi(4) potential to develop an inflection point, the quartic coupling lambda(phi) must exhibit a minimum with an almost vanishing value in its RG evolution, namely lambda(phi(1)) similar or equal to 0 and beta(lambda)(phi(1)) similar or equal to 0, where beta(lambda). is the beta function of the quartic coupling. As an example, we consider the minimal gauged B - L extended Standard Model at the TeV scale, where we identify the B - L Higgs field as the inflaton field. For a successful inflection-point inflation, which is consistent with the current cosmological observations, the mass ratios among the Z' gauge boson, the right-handed neutrinos and the B - L Higgs boson are fixed. Our scenario can be tested in the future collider experiments such as the high-luminosity LHC and the SHiP experiments. In addition, the inflection-point inflation provides a unique prediction for the running of the spectral index alpha similar or equal to -2.7 x 10(-3)(60/N)(2) (N is the e-folding number), which can be tested in the near future
Running non-minimal inflation with stabilized inflaton potential
No full textAbstract In the context of the Higgs model involving gauge and Yukawa interactions with the spontaneous gauge symmetry breaking, we consider λ ϕ 4 inflation with non-minimal gravitational coupling, where the Higgs field is identified as the inflaton. Since the inflaton quartic coupling is very small, once quantum corrections through the gauge and Yukawa interactions are taken into account, the inflaton effective potential most likely becomes unstable. In order to avoid this problem, we need to impose stability conditions on the effective inflaton potential, which lead to not only non-trivial relations amongst the particle mass spectrum of the model, but also correlations between the inflationary predictions and the mass spectrum. For concrete discussion, we investigate the minimal B - L extension of the standard model with identification of the B - L Higgs field as the inflaton. The stability conditions for the inflaton effective potential fix the mass ratio amongst the B - L gauge boson, the right-handed neutrinos and the inflaton. This mass ratio also correlates with the inflationary predictions. In other words, if the B - L gauge boson and the right-handed neutrinos are discovered in the future, their observed mass ratio provides constraints on the inflationary predictions
Hunting inflatons at FASER
No full textWe consider a nonminimal quartic inflation scenario in the minimal extension of the Standard Model (SM) with the classical conformal invariance, where the inflaton is identified with the Higgs field (). By virtue of the classically conformal invariance and the radiative symmetry breaking via the Coleman-Weinberg mechanism, the inflationary predictions (in particular, the tensor-to-scaler ratio ), the coupling , and the gauge boson mass are all determined by only two free parameters: the inflaton mass and its mixing angle with the SM Higgs field. FASER can search for a long-lived scalar, which is the inflaton in our scenario, for the parameter ranges and . Therefore, if such a scalar is discovered at FASER, both and would be fixed, leading to the predictions for , , and in our model. These predictions can be tested by future cosmological observations and LHC searches for the boson resonance
Heavy Majorana neutrino pair productions at the LHC in minimal U(1) extended Standard Model
No full textAbstract In our recent paper (Das et al. in Phys Rev D 97:115023, 2018) we explored a prospect of discovering the heavy Majorana right-handed neutrinos (RHNs) at the future LHC in the context of the minimal non-exotic U(1) extended Standard Model (SM), where a pair of RHNs are created via decay of resonantly produced massive U(1) gauge boson ( Z′ ). We have pointed out that this model can yield a significant enhancement of the branching ratio of the Z′ boson to a pair of RHNs, which is crucial for discovering the RHNs under the very severe LHC Run-2 constraint from the search for the Z′ boson with dilepton final states. In this paper, we perform a general parameter scan to evaluate the maximum production rate of the same-sign dilepton final states (smoking gun signature of Majorana RHNs production) at the LHC, while reproducing the neutrino oscillation data. We also consider the minimal non-exotic U(1) model with an alternative charge assignment. In this case, we find a further enhancement of the branching ratio of the Z′ boson to a pair of RHNs compared to the conventional case, which opens up a possibility of discovering the RHNs even before the Z′ boson at the future LHC experiment
Inflation, proton decay, and Higgs-portal dark matter in
No full textWe propose a simple non-supersymmetric grand unified theory (GUT) based on the gauge group . The model includes 3 generations of fermions in (), () and () representations. The -plets contain Standard Model (SM) fermions plus right-handed neutrinos, and the -plet and the singlet fermions are introduced to make the model anomaly-free. Gauge coupling unification at GeV is achieved by including an intermediate Pati–Salam breaking at GeV, which is a natural scale for the seesaw mechanism. For , proton decay will be tested by the Hyper-Kamiokande experiment. The extra fermions acquire their masses from symmetry breaking, and a Higgs field drives a successful inflection-point inflation with a low Hubble parameter during inflation, . Hence, cosmologically dangerous monopoles produced from SO(10) and PS breakings are diluted away. This is the first SO(10) model we are aware of in which relatively light intermediate mass ( GeV) primordial monopoles can be adequately suppressed. The reheating temperature after inflation can be high enough for successful leptogenesis. With the Higgs field contents of our model, a symmetry remains unbroken after GUT symmetry breaking, and the lightest mass eigenstate among linear combinations of the -plet and the singlet fermions serves as a Higgs-portal dark matter (DM). We identify the parameter regions to reproduce the observed DM relic density while satisfying the current constraint from the direct DM detection experiments. The present allowed region will be fully covered by the future direct detection experiments such as LUX-ZEPLIN DM experiment. In the presence of the extra fermions, the SM Higgs potential is stabilized up to
Inflection-point inflation with axion dark matter in light of Trans-Planckian Censorship Conjecture
No full textMotivated by the recently proposed Trans-Planckian Censorship Conjecture (TCC), we propose a gauged model of inflection-point inflation with axion dark matter. The Hubble scale during inflation () satisfies the TCC bound of GeV, the axion dark matter scenario is free from the axion domain wall and isocurvature problems. The seesaw mechanism is automatically incorporated in the model and the observed baryon asymmetry of the universe can be reproduced via resonant leptogenesis
Enhanced pair production of heavy Majorana neutrinos at the LHC
No full textTowards experimental confirmations of the type-I seesaw mechanism, we explore a prospect of discovering the heavy Majorana right-handed neutrinos (RHNs) from a resonant production of a new massive gauge boson () and its subsequent decay into a pair of RHNs () at the future high luminosity runs at the Large Hadron Collider (LHC). Recent simulation studies have shown that the discovery of the RHNs through this process is promising in the future. However, the current LHC data very severely constrains the production cross section of the boson into a dilepton final states, ( or ). Extrapolating the current bound to the future, we find that a significant enhancement of the branching ratio over is necessary for the future discovery of RHNs. As a well-motivated simple extension of the standard model (SM) to incorporate the boson and the type-I seesaw mechanism, we consider the minimal model, which is a generalization of the well-known minimal model without extending the particle content. We point out that this model can yield a significant enhancement up to (per generation). This is in sharp contrast with the minimal model, a benchmark scenario commonly used in simulation studies, which predicts (per generation). With such an enhancement and a realistic model-parameter choice to reproduce the neutrino oscillation data, we conclude that the possibility of discovering RHNs with, for example, a luminosity implies that the boson will be discovered with a luminosity of () for the normal (inverted) hierarchy of the light neutrino mass pattern
SU(5)×U(1)X grand unification with minimal seesaw and Z′-portal dark matter
No full textWe propose a grand unified SU(5)×U(1)X model, where the standard SU(5) grand unified theory is supplemented by minimal seesaw and a right-handed neutrino dark matter with an introduction of a global Z2-parity. In the presence of three right-handed neutrinos (RHNs), the model is free from all gauge and mixed-gravitational anomalies. The SU(5) symmetry is broken into the Standard Model (SM) gauge group at MGUT≃4×1016GeV in the standard manner, while the U(1)X symmetry breaking occurs at the TeV scale, which generates the TeV-scale mass of the U(1)X gauge boson (Z′ boson) and the three Majorana RHNs. A unique Z2-odd RHN is stable and serves as the dark matter (DM) in the present Universe, while the remaining two RHNs work to generate the SM neutrino masses through the minimal seesaw. We investigate the Z′-portal RHN DM scenario in this model context. We find that the constraints from the DM relic abundance, and the Z′ boson search at the Large Hadron Collider (LHC), and the perturbativity bound on the U(1)X gauge coupling are complementary to narrow down the allowed parameter region in the range of 3.0≤mZ′[TeV]≤9.2 for the Z′ boson mass. The allowed region for mZ′≤5TeV will be fully covered by the future LHC experiments. We also briefly discuss the successful implementation of Baryogenesis and cosmological inflation scenarios in the present model
