Standard Model Group Research Articles

Comparative Long-Term Clinical Performance of Mechanical Aortic Valve Prostheses

Aggregated data and long-term follow-up in national health data registers offer the opportunity to compare the performance of mechanical aortic prostheses within the same population. To investigate the clinical performance of mechanical aortic valve prostheses. This nationwide cohort study included all 5224 patients who underwent primary mechanical aortic valve replacement in Sweden between January 1, 2003, and December 31, 2018. Statistical analysis was performed between May and September 2023. Surgical aortic valve replacement with the On-X, Carbomedics, Bicarbon, Standard, Regent, Open Pivot, Masters, or Advantage valve models. The primary outcome was all-cause mortality, and secondary outcomes were reintervention, heart failure, major bleeding, stroke, and embolic events. Regression standardization was used to account for baseline differences. Overall, 5224 patients (mean [SD] age, 56.8 [11.7] years; 3908 men [74.8%]) were included. Total follow-up time was 43 982 person-years (mean [SD], 8.4 [4.6] years; maximum, 17.2 years). After regression standardization, there was a significant difference in 10-year mortality between the Carbomedics model group (17%; 95% CI, 15%-18%), Regent model group (17%; 95% CI, 13%-20%), and Standard model group (17%; 95% CI, 14%-19%) compared with the Bicarbon model group (27%; 95% CI, 21%-34%). In this cohort study of mechanical valve surgical aortic replacement outcomes in Sweden, the rate of all-cause mortality was higher in the Bicarbon group than in the Carbomedics, Regent, and Standard model groups. These findings warrant further research on the long-term clinical performance of the Bicarbon valve.

Unification of the four forces in the Spin(11,1) geometric algebra

SO(10), or equivalently its covering group Spin(10), is a well-known promising grand unified group that contains the standard-model group. The spinors of the group Spin(N) of rotations in N spacetime dimensions are indexed by a bitcode with [N/2] bits. Fermions in Spin(10) are described by five bits yzrgb, consisting of two weak bits y and z, and three colour bits r, g, b. If a sixth bit t is added, necessary to accommodate a time dimension, then the enlarged Spin(11, 1) algebra contains the standard-model and Dirac algebras as commuting subalgebras, unifying the four forces. The minimal symmetry breaking chain that breaks Spin(11, 1) to the standard model is unique, proceeding via the Pati-Salam group. The minimal Higgs sector is similarly unique, consisting of the dimension 66 adjoint representation of Spin(11, 1); in effect, the scalar Higgs sector matches the vector gauge sector. Although the unified algebra is that of Spin(11, 1), the persistence of the electroweak Higgs field after grand symmetry breaking suggests that the gauge group before grand symmetry breaking is Spin(10, 1), not the full group Spin(11, 1). The running of coupling parameters predicts that the standard model should unify to the Pati-Salam group Spin(4) w × Spin(6) c at 1012 GeV, and thence to Spin(10, 1) at 1015 GeV. The grand Higgs field breaks t-symmetry, can drive cosmological inflation, and generates a large Majorana mass for the right-handed neutrino by flipping its t-bit. The electroweak Higgs field breaks y-symmetry, and generates masses for fermions by flipping their y-bit.

Trinification from E6 symmetry breaking

In the context of E6 Grand Unified Theories (GUTs), an intriguing possibility for symmetry breaking to the Standard Model (SM) group involves an intermediate stage characterized by either SU(3) × SU(3) × SU(3) (trinification) or SU(6) × SU(2). The more common choices of SU(5) and SO(10) GUT symmetry groups do not offer such breaking chains. We argue that the presence of a real (rank 2 tensor) representation 650 of E6 in the scalar sector is the minimal and likely only reasonable possibility to obtain one of the novel intermediate stages. We analyze the renormalizable scalar potential of a single copy of the 650 and find vacuum solutions that support regularly embedded subgroups SU(3) × SU(3) × SU(3), SU(6) × SU(2), and SO(10) × U(1), as well as specially embedded subgroups F4 and SU(3) × G2 that do not contain the SM gauge symmetry. We show that for a suitable choice of parameters, each of the regular cases can be obtained as the lowest among the analyzed minima in the potential.

Co-Management Reduces Mortality in Post-Sternotomy Mediastinitis.

Background: Post-sternotomy mediastinitis (PSM) is one of the most feared complications of cardiac surgery. The impact of a multidisciplinary management approach on this pathology is yet unknown. Patients and Methods: A multidisciplinary approach based on a co-management model (CMM) of care was initiated in January 2018 because of the incorporation of a hospitalist unit on a cardiac surgery department. An observational retrospective cohort study was designed to evaluate the impact of the CMM of care compared to the standard model (SM) of care in patients diagnosed with PSM. Our primary and secondary outcomes were survival time and treatment failure rate (two or more surgical procedures needed to solve PSM or PSM-related death), respectively. Data related to patient death date were collected from the Spanish National Death Index. A multivariable Cox regression model was created using those variables believed to be clinically relevant. Results: Ninety-one patients developed PSM from January 2010 to June 2020. Regarding the pre-operative clinical status, surgical procedure, and PSM severity, both groups had similar baseline characteristics. Patients were followed for a mean of 27.54 ± 30.5 months. A total of 60.3% of the SM group and 11.1% of the CMM group (p < 0.001) died. Treatment failure occurred in 53 patients (72.6%) in the SM group versus 7 (38.6%) in the CMM group (p = 0.007). The CMM independently reduced overall mortality (hazard ratio [HR], 0.11; 95% confidence interval [CI]. 0.01-0.83) and treatment failure rate (HR, 0.01; 95% CI, 0.001-0.183). Gram-positive bacterial infection (HR, 3.73; 95% CI, .6-8.3), and complete osteosynthesis material removal (HR, 0.47; 95% CI, 0.24-0.91) also influenced mortality in our model. Conclusions: A co-management care model reduced overall mortality in patients diagnosed with post-sternotomy mediastinitis.

Anomaly-free ALP from non-Abelian flavor symmetry

Motivated by the XENON1T excess in electron-recoil measurements, we investigate the prospects of probing axion-like particles (ALP) in lepton flavor violation experiments. In particular, we identify such ALP as a pseudo-Goldstone from the spontaneous breaking of the flavor symmetries that explain the mixing structure of the Standard Model leptons. We present the case of the flavor symmetries being a non-Abelian U(2) and the ALP originating from its U(1) subgroup, which is anomaly-free with the Standard Model group. We build two explicit realistic examples that reproduce leptonic masses and mixings and show that the ALP which is consistent with XENON1T anomaly could be probed by the proposed LFV experiments.

Development, optimization, and validation of Inflammatory Bowel Disease rat model using isotretinoin

Backgroundand Purpose: Inflammatory Bowel Disease (IBD) is a persistent bio-psychological disorder with the absence of actual pathological reason. Association between IBD and isotretinoin has been reported by many human and in vitro studies. However, in this study, our focus is on finding the causal relationship between IBD and isotretinoin for the development of a new animal model. MethodsTwenty-eight Sprague Dawley rats were taken for this study and divided into five groups (i.e. Group 1: Normal control, Group 2: Standard IBD Model Group (Indomethacin treated), Group 3: Isotretinoin low dose (7 mg/kg), Group 4: Isotretinoin medium dose (35 mg/kg), Group 5: Isotretinoin high dose (70 mg/kg). The rats were treated according to assigned treatment and observed on different days to evaluate the severity of IBD with the help of symptomatical (nausea, diarrhea, stool consistency, etc.) activity, biochemical parameters, macroscopy, and histological analyses. Key resultsDuring the entire study period, body weight, stool consistency and frequency of the animals had been observed daily. No significant reduction in body weight was observed between the disease induced and normal control animals; however, it was observed that the stool consistency of the animals became less (mucus in stool) day by day and stool frequency increased (frequent defecation) in the different isotretinoin groups compared to the control group. There was statistically significant increase in TBARS levels of isotretinoin low (p < 0.05), medium (p < 0.001) and high dose (p < 0.01) treated group was observed, as compared to control group. Similarly, statistically significant effects of isotretinoin on GSH level (p < 0.01), CAT activity (p < 0.01), and SOD (p < 0.01) were also observed. Increase in TNF-α levels found significantly higher in isotretinoin medium dose (35 mg/kg) treated group (p < 0.001) as compared with control group as well as standard IBD model group. All the three-isotretinoin treated groups (Isotretinoin low dose: p < 0.001; Isotretinoin medium dose: p < 0.001; Isotretinoin high dose: p < 0.001) depicted significant difference in macroscopic scores as compared with control group; these results are comparable with standard IBD model group. Histological analyses revealed that, among three-dose groups of isotretinoin, there was excessive amount of crypt abscesses, infiltration of inflammatory cells, and formation of ulceration observed in isotretinoin medium dose treated group. ConclusionAs standard indomethacin treated group, isotretinoin also caused significant damage to intestinal mucosa, and form ulceration in gastrointestinal tract. Compared to control group, isotretinoin significantly worsens the disease condition, which were comparable to the indomethacin-treated group; however, isotretinoin at the dose of 35 mg/kg caused maximum severe damage to the intestinal mucosa.

Quantum nature of the minimal potentially realistic SO(10) Higgs model

We study several aspects of the quantum structure of the minimal potentially realistic renormalizable $\mathrm{SO}(10)$ Higgs model in which the $\mathbf{45}\oplus \mathbf{126}$ scalars spontaneously break the symmetry down to the Standard Model group $\mathrm{SU}(3)_{c}\times \mathrm{SU}(2)_{L}\times \mathrm{U}(1)_{Y}$. With a complete information about the one-loop corrections to the masses of all scalars in the theory and the one-loop beta functions governing the running of all dimensionless scalar self-couplings, the domains of the parameter space where the model can be treated perturbatively are established, along with improved bounds from the requirements of the SM vacuum stability and gauge coupling unification. We demonstrate that the model is fully consistent and potentially realistic only in very narrow regions of the parameter space corresponding to the breaking chains with well pronounced $\mathrm{SU}(4)_{C}\times \mathrm{SU}(2)_L\times \mathrm{U}(1)_R$ and $\mathrm{SU}(3)_{c}\times \mathrm{SU}(2)_L\times \mathrm{SU}(2)_R\times \mathrm{U}(1)_{B-L}$ intermediate symmetries, with a clear preference for the former case. Barring accidental fine-tunings in the scalar sector, this makes it possible to provide a very sharp prediction for the position of the unification scale and the value of the associated gauge coupling, with clear implications for the phenomenology of grand unified models based on this structure.

U(1)' extensions of the mu nu mathrm{SSM}

In the mu nu SSM, the presence of R-parity violating couplings involving right-handed (RH) neutrinos solves simultaneously the mu - and nu -problems. We explore extensions of the mu nu SSM adding a U(1)' gauge group, which provides the RH neutrinos with a non-vanishing charge. In these models, dubbed Umu nu SSM, the anomaly cancellation conditions impose the presence of exotic quarks in the spectrum that are vector-like under the standard model (SM) gauge group: either three pairs SU(2) quark singlets, or a pair of quark singlets together with a pair of quark doublets. Several singlets under the SM group can also be present, with the U(1)' charges making distinctions among them, and therefore allowing different types of couplings. Some of these singlets dynamically generate Majorana masses for the RH neutrinos, and others can be candidates for dark matter. The useful characteristics of models with U(1)'s are also present in Umu nu SSM models: baryon-number-violating operators as well as explicit Majorana masses and mu terms are forbidden, and the domain wall problem is avoided. The phenomenology of Umu nu SSM models is very rich. We analyze the experimental constraints on their parameter space, specially on the mass and mixing of the new Z' boson. In addition to the exotic quarks, which can hadronize inside the detector or decay producing SM particles, the Umu nu SSM models can also have new signals such as decays of the Z' to sparticle pairs like right sneutrinos, charginos or neutralinos. Besides, Z' and Higgs mediated annihilations and interactions with the visible sector of WIMP dark matter particles, can also be present.

TetrahedralA4symmetry in anti-SU(5) GUT

We construct a flavor model in an anti-SU(5) GUT with a tetrahedral symmetry $A_4$. We choose a basis where $Q_{text{em}}=-\frac13$ quarks and charged leptons are already mass eigenstates. This choice is possible from the $A_4$ symmetry. Then, matter representation $\overline{10}_{-1}^{\rm\, matter}$ contains both a quark doublet and a heavy neutrino $N$, which enables us to use the $A_4$ symmetry to both $Q_{text{em}}=+\frac23$ quark masses and neutrino masses (through the see-saw via $N$). This is made possible because the anti-SU(5) breaking is achieved by the Higgs fields transforming as anti-symmetric representations of SU(5), $\overline{10}_{-1}^H\oplus 10_{+1}^H$, reducing the rank-5 anti-SU(5) group down to the rank-4 standard model group \smg. For possible mass matrices, the $A_4$ symmetry predictions on mass matrices at field theory level are derived. Finally, an illustration from string compactification is presented.

Addressing the RD(*) anomalies with an S1 leptoquark from SO(10) grand unification

Motivated by the $R_{D^{(*)}}$ anomalies, we investigate an $\mathrm{SO}(10)$ grand unification scenario where a charge $-1/3$ scalar leptoquark ($S_1$) remains as the only new physics candidate at the TeV scale. This leptoquark along with the Standard Model (SM) Higgs doublet originates from the same 10-dimensional real scalar multiplet in the $\mathrm{SO}(10)$ grand unification framework taking its mass close to the electroweak scale. We explicitly show how the gauge coupling unification is achieved with only one intermediate symmetry-breaking scale at which the Pati-Salam gauge group is broken into the SM group. We investigate the phenomenological implications of our scenario and show that an $S_1$ with a specific Yukawa texture can explain the $R_{D^{(*)}}$ anomalies. We perform a multiparameter scan considering the relevant flavour constraints on $R_{D^{(*)}}$, $F_L{(D^*)}$, $P_\tau(D^*)$ and $R_{K^{(*)}}^{\nu\nu}$ as well as the constraint coming from the $Z\to\tau\tau$ decay and the latest $\tau\tau$ resonance search data at the LHC. Our analysis shows that a single leptoquark solution to the observed $R_{D^{(*)}}$ anomalies with $S_1$ is still a viable solution.

On C $$\varvec{\otimes }$$ H $$\varvec{\otimes }$$ O-Valued Gravity, Sedenions, Hermitian Matrix Geometry and Nonsymmetric Kaluza–Klein Theory

We review briefly how R $$\otimes $$ C $$\otimes $$ H $$\otimes $$ O-valued gravity (real-complex-quaterno-octonionic gravity) naturally can describe a grand unified field theory of Einstein’s gravity with a Yang–Mills theory containing the Standard Model group $$SU(3) \times SU(2) \times U(1)$$ . The algebra of left actions associated with the composite algebras involving the Division algebras, and the Sedenions $$\mathbf{S}$$ , and acting on themselves, all lead to complex Clifford algebras (complex matrix algebras). The complex Cl(16) algebra is the most appealing one since it is the one corresponding to the algebra of left actions of $$\mathbf{C} \otimes \mathbf{H} \otimes \mathbf{O} \otimes \mathbf{S}$$ acting on itself, and containing the $$\mathbf{e_8 \oplus e_8}$$ algebra of the anomaly free 10D Heterotic String. An analysis of $$ C \otimes H \otimes O$$ -valued gravity reveals that it bears a connection to Nonsymmetric Kaluza–Klein theories and complex Hermitian Matrix Geometry. The key behind these connections is in finding the relation between $$ C \otimes H \otimes O$$ -valued metrics in two complex dimensions with complex metrics in higher dimensional real manifolds ( $$ D = 32 $$ real dimensions in particular). It is desirable to extend these results to hypercomplex, quaternionic manifolds and Exceptional Jordan Matrix Models.

Kinetic mixing and portal matter phenomenology

Dark photons (DP) are interesting as potential mediators between the dark matter (DM) sector and the fields of the Standard Model (SM). The interaction of the DP, described by a broken $U(1)_D$ gauge symmetry, with the SM is usually generated at the one-loop level via kinetic mixing through the existence of portal matter (PM), here assumed to be fermionic, which carries both a dark charge as well as a SM $U(1)_Y$ hypercharge. For theoretical consistency, as well as for many phenomenological reasons, this PM must be vector-like with respect to the SM and dark gauge groups and, in particular, is shown to be allowed only to transform as vector-like copies of the usual SM fields. The dark Higgs that is responsible for the breaking of $U(1)_D$ can then generate a mixing between the PM and SM fields with the same electric charge thus altering the DP interactions with (at least some of) the SM fields and also providing a path for the PM fields to decay. In this paper we briefly explore the phenomenology of some specific simple models of this PM including, for the case where the PM is leptonic in nature, their potential impact on experiments probing low energy parity-violation and the g-2 of the muon. In the case of color-triplet, bottom quark-like PM, their direct pair- and single-production at the LHC is shown to be observable in final states that include missing $E_T$ and/or very highly boosted lepton-jets together with pairs of high $p_T$ b-jets that can be used to trigger on such events. These signatures are quite distinct from those usually employed in the search for vector-like quarks at the LHC and, furthermore, we demonstrate that the conventional signal channels for vector-like quarks involving the SM Higgs and gauge fields are essentially closed in the case of PM.

R $$\otimes $$ ⊗ C $$\otimes $$ ⊗ H $$\otimes $$ ⊗ O-Valued Gravity as a Grand Unified Field Theory

It is argued how R $$\otimes $$ C $$\otimes $$ H $$\otimes $$ O-valued Gravity (real-complex-quaterno-octonionic Gravity) naturally can describe a Grand Unified Field theory of Einstein’s gravity with a Yang-Mills theory containing the Standard Model group $$SU(3) \times SU(2) \times U(1)$$ . In particular, it leads to a $$[SU(4)]^4$$ symmetry group revealing the possibility of extending the standard model by introducing additional gauge bosons, heavy quarks and leptons, and an extra fourth family of fermions. We finalize by displaying the analog of the Einstein–Hilbert action for $$\mathbf{R} \otimes \mathbf{C} \otimes \mathbf{H} \otimes \mathbf{O}$$ -valued gravity via the use of matrices, and which is based on “coloring” the graviton; i.e. by attaching internal indices to the metric $$g_{\mu \nu }$$ . In the most general case, U(16) arises as the isometry group, while U(8) is the isometry group in the split-octonion case.

Safety and efficacy of switching from unfractionated heparin to bivalirudin during primary percutaneous coronary intervention.

To evaluate the safety and efficacy of switching to bivalirudin during primary percutaneous coronary intervention (PCI) for patients who received preprocedure unfractionated heparin (UFH). Current guidelines favor bivalirudin for primary PCI in patients at high risk of bleeding, particularly when femoral access is used. However, patients with ST-segment elevation myocardial infarction frequently receive UFH before arrival in the catheterization laboratory. Scientific databases and websites were searched for randomized controlled trials. Patients were divided into those who received heparin with or without glycoprotein IIb/IIIa inhibitors (heparin group); those switched to bivalirudin during primary PCI from preprocedure UFH (switch group); and those who received bivalirudin without preprocedure UFH (Biv-alone group). Both traditional pairwise meta-analyses using moderator analyses and network meta-analyses using mixed-treatment comparison models were performed. Data from five trials including13,547 patients were analyzed. In mixed-comparison models, switching to bivalirudin during primary PCI was associated with lower rates for all-cause mortality and major adverse cardiovascular events (MACEs) compared to the other strategies. Rates for all-cause mortality, MACEs, and net adverse clinical events (NACEs) were similar for the heparin and Biv-alone groups. Switching strategies was also associated with lower major bleeding rates compared to heparin alone. Similarly, in a standard pairwise model, both the switch and Biv-alone groups were associated with decreased bleeding risk compared to the heparin group. However, only the switch strategy was associated with decreased all-cause mortality (RR, 0.47; 95% CI, 0.30-0.75; P = 0.001), MACE (RR, 0.67; 95% CI, 0.49-0.91; P = 0.012), and NACE (RR, 0.61; 95% CI, 0.41-0.92; P = 0.019) compared with heparin alone. During primary PCI, use of bivalirudin for those receiving preprocedure UFH was associated decreased rates for major bleeding, NACEs, MACEs, and all-cause mortality compared to heparin +/- GPI. This strategy was also associated with decreased rates for MACEs and all-cause mortality compared to bivalirudin alone without preprocedure UFH.

Heterotic line bundle models on elliptically fibered Calabi-Yau three-folds

We analyze heterotic line bundle models on elliptically fibered Calabi-Yau three-folds over weak Fano bases. In order to facilitate Wilson line breaking to the standard model group, we focus on elliptically fibered three-folds with a second section and a freely-acting involution. Specifically, we consider toric weak Fano surfaces as base manifolds and identify six such manifolds with the required properties. The requisite mathematical tools for the construction of line bundle models on these spaces, including the calculation of line bundle cohomology, are developed. A computer scan leads to more than 400 line bundle models with the right number of families and an SU(5) GUT group which could descend to standard-like models after taking the ℤ2 quotient. A common and surprising feature of these models is the presence of a large number of vector-like states.

Sodium butyrate attenuates high-fat diet-induced steatohepatitis in mice by improving gut microbiota and gastrointestinal barrier.

To investigate whether gut microbiota metabolite sodium butyrate (NaB) is an effective substance for attenuating non-alcoholic fatty liver disease (NAFLD) and the internal mechanisms. Male C57BL/6J mice were divided into three groups, normal control were fed standard chow and model group were fed a high-fat diet (HFD) for 16 wk, the intervention group were fed HFD for 16 wk and treated with NaB for 8 wk. Gut microbiota from each group were detected at baseline and at 16 wk, liver histology were evaluated and gastrointestinal barrier indicator such as zonula occluden-1 (ZO-1) were detected by immunohistochemistry and realtime-PCR, further serum or liver endotoxin were determined by ELISA and inflammation- or metabolism-associated genes were quantified by real-time PCR. NaB corrected the HFD-induced gut microbiota imbalance in mice, while it considerably elevated the abundances of the beneficial bacteria Christensenellaceae, Blautia and Lactobacillus. These bacteria can produce butyric acid in what seems like a virtuous circle. And butyrate restored HFD induced intestinal mucosa damage, increased the expression of ZO-1 in small intestine, further decreased the levels of gut endotoxin in serum and liver compared with HF group. Endotoxin-associated genes such as TLR4 and Myd88, pro-inflammation genes such as MCP-1, TNF-α, IL-1, IL-2, IL-6 and IFN-γ in liver or epididymal fat were obviously downregulated after NaB intervention. Liver inflammation and fat accumulation were ameliorated, the levels of TG and cholesterol in liver were decreased after NaB intervention, NAS score was significantly decreased, metabolic indices such as FBG and HOMA-IR and liver function indicators ALT and AST were improved compared with HF group. NaB may restore the dysbiosis of gut microbiota to attenuate steatohepatitis, which is suggested to be a potential gut microbiota modulator and therapeutic substance for NAFLD.

The spontaneous ℤ 2 $$ {\mathbb{Z}}_2 $$ breaking Twin Higgs

The Twin Higgs model seeks to address the little hierarchy problem by making the Higgs a pseudo-Goldstone of a global $SU(4)$ symmetry that is spontaneously broken to $SU(3)$. Gauge and Yukawa couplings, which explicitly break $SU(4)$, enjoy a discrete $\mathbb{Z}_2$ symmetry that accidentally maintains $SU(4)$ at the quadratic level and therefore keeps the Higgs light. Contrary to most beyond the Standard Model theories, the quadratically divergent corrections to the Higgs mass are cancelled by a mirror sector, which is uncharged under the Standard Model groups. However, the Twin Higgs with an exact $\mathbb{Z}_2$ symmetry leads to equal vevs in the Standard Model and mirror sectors, which is phenomenologically unviable. An explicit $\mathbb{Z}_2$ breaking potential must then be introduced and tuned against the $SU(4)$ breaking terms to produce a hierarchy of vevs between the two sectors. This leads to a moderate but non-negligible tuning. We propose a model to alleviate this tuning, without the need for an explicit $\mathbb{Z}_2$ breaking sector. The model consists of two $SU(4)$ fundamental Higgses, one whose vacuum preserves $\mathbb{Z}_2$ and one whose vacuum breaks it. As the interactions between the two Higgses are turned on, the $\mathbb{Z}_2$ breaking is transmitted from the broken to the unbroken sector and a small hierarchy of vevs is naturally produced. The presence of an effective tadpole and feedback between the two Higgses lead to a sizable improvement of the tuning. The resulting Higgs boson is naturally very Standard Model like.

Hypercharge flux in heterotic compactifications

We study heterotic Calabi-Yau models with hypercharge flux breaking, where the visible E8 gauge group is directly broken to the standard model group by a non-flat gauge bundle, rather than by a two-step process involving an intermediate grand unified theory and a Wilson line. It is shown that the required alternative E8 embeddings of hypercharge, normalized as required for gauge unification, can be found and we classify these possibilities. However, for all but one of these embeddings we prove a general no-go theorem which asserts that no suitable geometry and vector bundle leading to a standard model spectrum can be found. Intuitively, this happens due to the large number of index conditions which have to be imposed in order to obtain a correct physical spectrum in the absence of an underlying grand unified theory.

Heavy vector triplets: bridging theory and data

We introduce a model-independent strategy to study narrow resonances which we apply to a heavy vector triplet of the Standard Model (SM) group for illustration. The method is based on a simplified phenomenological Lagrangian which reproduces a large class of explicit models. Firstly, this allows us to derive robust model-independent phenomenological features and, conversely, to identify the peculiarities of different explicit realizations. Secondly, limits on cross-section times BR can be converted into bounds on a few relevant parameters in a fully analytic way, allowing for an interpretation in any given explicit model. Based on the available 8 TeV LHC analyses, we derive current limits and interpret them for vector triplets arising in weakly coupled (gauge) and strongly coupled (composite) extensions of the SM. We point out that a model-independent limit setting procedure must be based on purely on-shell quantities, like a cross-section times BR. Finite width effects altering the limits can be considerably reduced by focusing on the on-shell signal region. We illustrate this aspect with a study of the invariant mass distribution in di-lepton searches and the transverse mass distribution in lepton-neutrino final states. In addition to this paper we provide a set of online tools available at a dedicated webpage.

A heterotic standard model with B − L symmetry and a stable proton

We consider heterotic Calabi-Yau compactifications with S(U(4)xU(1)) background gauge fields. These models lead to gauge groups with an additional U(1) factor which, under certain conditions, can combine with hypercharge to a B-L symmetry. The associated gauge boson is automatically super-massive and, hence, does not constitute a phenomenological problem. We illustrate this class of compactifications with a model based on the monad construction, which leads to a supersymmetric standard model with three families of quarks and leptons, one pair of Higgs doublets, three right-handed neutrinos and no exotics charged under the standard model group. The presence of the B-L symmetry means that the model is safe from proton decay induced by dimension four operators. Due to the presence of a special locus in moduli space where the bundle structure group is Abelian and the low-energy symmetry enhances we can also show the absence of dimension five proton-decay inducing operators.