One-loop Contributions Research Articles

Precise prediction for the Higgs-Boson masses in the {varvec{mu }}{varvec{nu }}SSM with three right-handed neutrino superfields

The mu nu mathrm {SSM} is a simple supersymmetric extension of the Standard Model (SM) capable of describing neutrino physics in agreement with experiments. We perform the complete one-loop renormalization of the neutral scalar sector of the mu nu mathrm {SSM} with three generation of right-handed neutrinos in a mixed on-shell/smash {overline{mathrm {DR}}} scheme. We calculate the full one-loop corrections to the neutral scalar masses of the mu nu mathrm {SSM}. The one-loop contributions are supplemented by available MSSM higher-order corrections. We obtain numerical results for a SM-like Higgs-boson mass consistent with experimental bounds, while simultaneously agreeing with neutrino oscillation data. We illustrate the distinct phenomenology of the mu nu mathrm {SSM} in scenarios in which one or more right-handed sneutrinos are lighter than the SM-like Higgs boson, which might be substantially mixed with them. These scenarios are experimentally accessible, on the one hand, through direct searches of the right-handed sneutrinos decaying into SM particles, and on the other hand, via the measurements of the SM-like Higgs-boson mass and its couplings. In this way the parameter space of the mu nu mathrm {SSM} can be probed without the need to propose model dependent searches at colliders. Finally, we demonstrate how the mu nu mathrm {SSM} can simultaneously accommodate two excesses measured at LEP and LHC at sim 96,, mathrm {GeV} at the 1sigma level, while at the same time reproducing neutrino masses and mixings in agreement with neutrino oscillation measurements.

Flavor changing neutral current decays trightarrow c X (X=gamma ,,g,, Z,, H) and trightarrow c{{bar{ell }}}ell (ell =mu ,,tau ) via scalar leptoquarks

The flavor changing neutral current decays trightarrow c X (X=gamma ,,g,, Z,, H) and trightarrow c{{bar{ell }}}ell (ell =mu ,,tau ) are studied in a renormalizable scalar leptoquark (LQ) model with no proton decay, where a scalar SU(2) doublet with hypercharge Y=7/6 is added to the standard model, yielding a non-chiral LQ varOmega _{5/3}. Analytical results for the one-loop (tree-level) contributions of a scalar LQ to the f_irightarrow f_j X (f_irightarrow f_j {bar{f}}_m f_l) decays, with f_a=q_a, ell _a, are presented. We consider the scenario where varOmega _{5/3} couples to the fermions of the second and third families, with its right- and left-handed couplings obeying lambda _R^{ell u_i}/lambda _L^{ell u_i}=O(epsilon ), where epsilon parametrizes the relative size between these couplings. The allowed parameter space is then found via the current constraints on the muon (g-2), the tau rightarrow mu gamma decay, the LHC Higgs boson data, and the direct LQ searches at the LHC. For m_{varOmega _{5/3}}=1 TeV and epsilon =10^{-3}, we find that the trightarrow c X branching ratios are of similar size and can be as large as 10^{-8} in a tiny area of the parameter space, whereas {mathrm{Br}}(trightarrow c{{bar{tau }}}tau ) [{mathrm{Br}}(trightarrow c{{bar{mu }}}mu )] can be up to 10^{-6} (10^{-7}).

Naturalness in D-brane inspired models

We examine the naturalness of the D-brane inspired model constructed in flipped SU(5) supplemented with vector-like particles at the TeV scale, dubbed flippons. We find the model can produce a mainly Higgsino-like lightest supersymmetric particle (LSP) and small light stops, as favored by naturalness. In fact, a large trilinear scalar At term at the electroweak (EW) scale creates a large mass splitting between the top squarks, driving the light stop to near degeneracy with an LSP that is almost all Higgsino, with Delta Mleft({tilde{t}}_1,{tilde{chi}}_1^0right) < 5GeV, evading the LHC constraint on {tilde{t}}_1to c{tilde{chi}}_1^0 thus far. Given the smallness of the light stop, generating a 125 GeV light Higgs boson mass is aided by one-loop contributions from the Yukawa couplings between the flippons and Higgs fields. The resulting parameter space satisfying naturalness is rather constrained, thus we assess its viability by means of comparison to the LHC constraint on soft charm jets and direction detection limits on spin-independent cross-sections. Finally, we compute the level of electroweak fine-tuning and uncover a region with ΔEW< 30, i.e., fine-tuning better than 3%, regarded as low electroweak fine-tuning. Given the small light stop, the electroweak fine-tuning from only the top squarks is of mathcal{O} (1), indicating no fine-tuning from neither the light stop {tilde{t}}_1 nor the heavy stop {tilde{t}}_2 .

Searching for scalar boson decaying into light Z' boson at collider experiments in U(1)_{L_mu - L_tau } model

We study a model with U(1)_{L_mu - L_tau } gauge symmetry and discuss collider searches for a scalar boson, which breaks U(1)_{L_mu - L_tau } symmetry spontaneously, decaying into light Z' gauge boson. In this model, the new gauge boson, Z', with a mass lighter than {mathcal {O}}(100) MeV, plays a role in explaining the anomalous magnetic moment of muon via one-loop contribution. For the gauge boson to have such a low mass, the scalar boson, phi with {mathcal {O}}(100) GeV mass appears associated with the symmetry breaking. We investigate experimental constraints on U(1)_{L_mu - L_tau } gauge coupling, kinetic mixing, and mixing between the SM Higgs and phi . Then collider search is discussed considering phi production followed by decay process phi rightarrow Z' Z' at the large hadron collider and the international linear collider. We also estimate discovery significance at the linear collider taking into account relevant kinematical cut effects.

Relativistic cosmological large scale structures at one-loop

The large scale structure bispectrum in the squeezed limit couples large with small scales. Since relativity is important at large scales and non-linear loop corrections are important at small scales, the proper calculation of the observed bispectrum in this limit requires a non-linear relativistic calculation. We compute the matter bispectrum in general relativity in the weak field approximation. The calculation is as involved as existing second-order results. We find several differences with the Newtonian calculation such as the non-cancellation of IR divergences, the need to renormalize the background, and the fact that initial conditions must be set at second order in perturbation theory. For the bispectrum, we find relativistic corrections to be as large as the newtonian result in the squeezed limit. In that limit relativistic one-loop contributions, which we compute for the first time, can be as large as tree level results and have the same 1/k2 dependence as a primordial local non-Gaussianity signal where k is the momentum approaching zero. Moreover, we find the time dependence of the relativistic corrections to the bispectrum to be the same as that of a primordial non-Gaussianity signal.

B anomalies and dark matter: a complex connection

We study an extension of the Standard Model that addresses the hints of lepton flavour universality violation observed in Brightarrow K^{(*)} l^+l^- decays at LHCb, while providing a viable candidate for dark matter. The model incorporates two new scalar fields and a Majorana fermion that induce one-loop contributions to B meson decays. We show that agreement with observational data requires the new couplings to be complex and that the Majorana fermion can reproduce the observed dark matter relic density. This combination of cosmological and flavour constraints sets an upper limit on the dark matter and mediator masses. We have studied LHC dijet and dilepton searches, finding that they rule out large regions of parameter space by setting lower bounds on the dark matter and mediator masses. In particular, dilepton bounds are much more constraining in a future high-luminosity phase. Finally, we have computed the scattering cross section of dark matter off nuclei and compared it to the sensitivity of current and future direct detection experiments, showing that parts of the parameter space could be accessible in the future to multi-ton experiments. Future collider and direct DM searches complement each other to probe large areas of the parameter space of this model.

Fermions and scalars in [formula omitted] Wilson loops at strong coupling and beyond

We study the null polygonal Wilson loops/gluon scattering amplitudes in planar N=4 SYM by means of the pentagon Operator Product Expansion (OPE) series and its integrability features, with particular attention on the strong coupling expansion. Actually, at all couplings and for the hexagon we disentangle the SU(4) matrix structure of the squared form factors for fermions, organising them in Young diagrams similar to those previously used for scalars. Then, we concentrate on the strong coupling regime and show the appearance of a new (effective) particle in the series: the fermion-antifermion bound state, the so-called ‘meson’. Of course, we identify its interaction with itself in the OPE series, with formation of (effective) bound states, and with the gluons and bound states of them. All together these extract from the OPE series the AdS5 minimal area result for the Wilson loop, described by a set of Thermodynamic Bethe Ansatz (TBA)-like equations, and highlight also all the one-loop contributions. Moreover, the same strategy applies to N=2 Nekrasov partition function via the parallel meson/instanton. Eventually, to complete the strong coupling analysis, we consider the scalar sector for any polygon, confirming the emergence of a non-perturbative contribution from the string in S5, which eludes and corrects the minimal area argument.

New physics implication of Higgs precision measurements

Studying the properties of the Higgs boson can be an important window to explore the physics beyond the Standard Model (SM). In this work, we present studies on the implications of the Higgs precision measurements at future Higgs Factories. We perform a global fit to various Higgs search channels to obtain the 95% C.L. constraints on the model parameter spaces of two-Higgs Doublet Model (2HDM) and Minimal Supersymmetric Standard Model (MSSM). In the 2HDM, we analyze tree-level effects as well as one-loop contributions from the heavy Higgs bosons. The strong constraints on [Formula: see text], heavy Higgs masses and their mass splitting are complementary to direct search of the LHC as well as possible future [Formula: see text] pole precision measurements. For the MSSM, we study both the Higgs couplings and mass precisions. The constraints on the CP-odd Higgs mass [Formula: see text] and stop mass scale [Formula: see text] can be complementary to the direct search of HL-LHC. We also compare the sensitivity of various future Higgs factories, namely, Circular Electron Positron Collider (CEPC), Future Circular Collider (FCC)-ee and International Linear Collider (ILC).

One-loop QCD contributions to differential cross-sections for Higgs production at N3LO

We present one-loop contributions to the fully differential Higgs boson gluon-fusion cross-section for Higgs production via gluon fusion. Our results constitute a necessary ingredient of a complete N3LO determination of the cross-section. We perform our computation using a subtraction method for the treatment of soft and collinear singularities. We identify the infrared divergent parts in terms of universal splitting and eikonal functions, and demonstrate how phase-space integrations yield poles (up to 1/ε6) in the dimensional regulator ε = (4 − d)/2. We compute the coefficients of the ε expansion, including the finite part numerically. As a demonstration of our numerical implementation, we present the corrections at N3LO due to one-loop amplitudes in the rapidity and transverse momentum of the Higgs boson.

Probing low energy scalar leptoquarks by the leptonic W and Z couplings

We compute the generic one-loop contribution involving scalar leptoquarks (LQ) to the W and Z leptonic decay widths. In our computation we include for the first time the finite terms and the corrections due to the external momenta of the electroweak bosons, which is a step beyond the leading-logarithmic approximation considered in the literature so far. We show that the terms we include can be numerically quite significant. They amount to about 20% for scalar LQ masses below 1.5 TeV, as currently allowed by the direct searches at the LHC. To further illustrate the relevance of our results we revisit a model with two light scalar LQs, proposed to accommodate the B-physics anomalies. We show that the finite terms we computed can reduce the tension with the Z-pole data.

Double scaling limit of mathcal{N} = 2 chiral correlators with Maldacena-Wilson loop

We consider mathcal{N} = 2 conformal QCD in four dimensions and the one-point correlator of a class of chiral primaries with the circular frac{1}{2} -BPS Maldacena-Wilson loop. We analyze a recently introduced double scaling limit where the gauge coupling is weak while the R-charge of the chiral primary Φ is large. In particular, we consider the case Φ = (Trφ2)n, where φ is the complex scalar in the vector multiplet. The correlator defines a non-trivial scaling function at fixed κ = ngYM2 and large n that may be studied by localization. For any gauge group SU(N) we provide the analytic expression of the first correction ~ ζ(3)κ2 and prove its universality. In the SU(2) and SU(3) theories we compute the scaling functions at order mathcal{O} (κ6). Remarkably, in the SU(2) case the scaling – function is equal to an analogous quantity describing the chiral 2-point functions leftlangle Phi overline{Phi}rightrangle in the same large R-charge limit. We conjecture that this SU(2) scaling function is computed at all-orders by a mathcal{N} = 4 SYM expectation value of a matrix model object characterizing the one-loop contribution to the 4-sphere partition function. The conjecture provides an explicit series expansion for the scaling function and is checked at order mathcal{O} (κ10) by showing agreement with the available data in the sector of chiral 2-point functions.

One-loop structure of the photon propagator in the standard model extension

We study radiative corrections on the photon propagator from the electroweak sector of the minimal Lorentz- and $CPT$-violating Standard Model Extension. We derive the most general Lorentz-violating ghost sector from BRST symmetry and renormalization theory. We introduce a Lorentz-violating nonlinear gauge that simplifies both the Higgs and gauge-sector extensions, which can be helpful in radiative corrections. At one loop, these sectors contribute to the $CPT$-even part of the photon propagator, characterized by the Riemann-type tensor $(k_F)_{\alpha\beta\mu\nu}$. We give exact results for the contributions to the SO(1,3) irreducible parts of $(k_F)_{\alpha \beta \mu \nu}$, namely, the Weyl-type tensor $(\hat{k}_F)_{\alpha \beta \mu \nu}$, the Ricci-type tensor $(k_F)_{\alpha \beta}$, and the curvature-type scalar $k_F$. In the Yukawa sector, one-loop contributions are ultraviolet finite, but most of them are unobservable due to finite renormalization. The only observable effect is a contribution proportional to $(k_F)_{\alpha \beta}$ that emerges via a dimension-6 term that is observer and gauge invariant. In the Higgs and gauge sectors, all the irreducible parts of the corresponding Riemann-type tensors receive divergent contributions, so they are observable. The only finite contribution corresponds to the dimension-6 term. We think of these contributions as radiative corrections to the renormalized tensors and assume that both effects are of the same order of magnitude to find bounds from vacuum birefringence and compare with the literature. Bounds on $(k_F)_{\alpha \beta}$ contributions, innocuous to birefringence, are also derived using limits on the renormalized tensor from Laser-Interferometer-Gravitational-Wave-Observatory data. We compare these bounds with the literature. Beta functions associated with $(\hat{k}_F)_{\alpha \beta \mu \nu}$ and $(k_F)_{\alpha \beta}$ are derived.

One-loop contribution to dark-matter-nucleon scattering in the pseudo-scalar dark matter model

Recent dark matter (DM) direct searches place very stringent constraints on the possible DM candidates proposed in extensions of the Standard Model. There are however models where these constraints are avoided. One of the simplest and most striking examples comes from a straightforward Higgs-portal pseudo-scalar DM model featured with a softly broken U(1) symmetry. In this model the tree-level DM-nucleon scattering cross section vanishes in the limit of zero momentum transfer. It has also been argued that the leading-order DM-nucleon cross section appears at the one-loop level. In this work we have calculated the exact cross section in the zero momentum transfer at the leading order i.e., at the one-loop level of perturbative expansion. We have concluded that, in agreement with expectations, the amplitude for the scattering process is UV finite and approaches zero in the limit of vanishing DM masses. Moreover, we made clear that the finite DM velocity correction at tree level is subdominant with respect to the one-loop contribution. Based on the analytic formulae, our numerical studies show that, for a typical choice of model parameters, the DM nuclear recoiling cross section is well below mathcal{O} (10−50 cm2), which indicates that the DM direct detection signal in this model naturally avoids present strong experimental limits on the cross section.

Pseudoscalar Higgs boson pair production at a photon-photon collision in the two Higgs doublet model

In this study, the direct pair production of the pseudoscalar Higgs boson at a photon-photon collision is analyzed in the context of two Higgs doublet model, taking account the complete one-loop contributions. In order to illustrate the effect of the new physics, four benchmark points scenarios, which are consistent with theoretical and current experimental constraints, are chosen in the type-I of THDM with an exact alignment limit. In these benchmark points, the CP even lightest Higgs boson ($h^0$) have the Standard Model like couplings to the gauge bosons. The effect of individual contributions from each type of one-loop diagrams on the total cross section are examined in detail. The dependence of total cross section on the center-of-mass energy is also presented at the various polarization configurations of the incoming photons. Moreover, the regions $m_{12}^2-\tan\beta$ and $m_A-\tan\beta$ in the parameter space of the THDM are scanned for some fixed values of other parameters. The box-type diagrams make a much larger contribution to the total cross section than the others at high energies. Total cross section can be enhanced by a two factor thanks to opposite polarized photons as well as threshold effects.

Supersymmetric gauged U(1)Lμ−Lτ model for neutrinos and the muon ( g−2 ) anomaly

The gauged $U(1)_{L_{\mu}-L_{\tau}}$ model can provide for additional contributions to the muon anomalous magnetic moment by means of a loop involving the $Z^{\prime}$ gauge boson. However, the parameter space of such models is severely constrained if one combines the latest muon $(g-2)$ data with various neutrino experiments, such as neutrino trident production, $\nu -e$ and $\nu -q$ elastic scattering, etc. In a supersymmetric $U(1)_{L_{\mu}-L_{\tau}}$ model, a larger region of parameter space opens up, thus enabling one to explore otherwise forbidden regions of parameter space in nonsupersymmetric models involving the new gauge coupling ($g_X$) and the mass of the $Z^\prime$ gauge boson ($M_{Z^{\prime}}$) . We show that the minimal model with the minimal supersymmetric Standard Model (MSSM) field content is strongly disfavored from $Z$-boson decay and neutrino data. We also show that the nonminimal model with two extra singlet superfields can lead to correct neutrino masses and mixing involving both tree-level and one-loop contributions. We find that, in this model, both muon $(g-2)$ and neutrino data may be simultaneously explained in a parameter region consistent with experimental observations. In addition, we observe that the muon $(g-2)$ anomaly can be accommodated even with higher values of electroweak sparticle masses compared to the MSSM. Charged lepton-flavor-violating processes (like $\mu\rightarrow e\gamma$, $\tau\rightarrow \mu\gamma$, etc.) may have potentially large branching ratios in this scenario. Depending on the magnitude of the supersymmetry contribution to these processes, they may constrain hitherto unconstrained regions of the $M_{Z^{\prime}}-g_X$ parameter space. However, we find that these branching fractions never exceed their upper bounds in a region where both muon $(g-2)$ and neutrino oscillation data can be simultaneously accommodated.

Remarks on the Chern-Simons photon term in the QED description of graphene

We revisit the Coleman-Hill theorem in the context of reduced planar QED. Using the global U(1) Ward identity for this non-local but still gauge invariant theory, we can confirm that the topological piece of the photon self-energy at zero momentum does not receive further quantum corrections apart from the potential one-loop contribution, even when considering the Lorentz non-invariant case due to the Fermi velocity $v_F<c$. This is of relevance to probe possible time parity odd dynamics in a planar sheet of graphene which has an effective description in terms of $(2+1)$-dimensional planar reduced QED.

Three-flavored nonresonant leptogenesis at intermediate scales

Leptogenesis can successfully explain the matter-antimatter asymmetry via out-of-equilibrium decays of heavy Majorana neutrinos in the early Universe. In this article, we focus on nonresonant thermal leptogenesis and the possibility of lowering its scale. In order to do so, we calculate the lepton asymmetry produced from the decays of one and two heavy Majorana neutrinos using three-flavored density matrix equations in an exhaustive exploration of the model parameter space. We find regions of the parameter space where thermal leptogenesis is viable at intermediate scales, $T\ensuremath{\sim}{10}^{6}\text{ }\text{ }\mathrm{GeV}$. However, the viability of thermal leptogenesis at such scales requires a certain degree of cancellation between the tree- and one-loop level contribution to the light neutrino mass matrix, and we quantify such fine-tuning.

κ -Poincaré invariant quantum field theories with Kubo-Martin-Schwinger weight

A natural star product for 4-d $\kappa$-Minkowski space is used to investigate various classes of $\kappa$-Poincar\'e invariant scalar field theories with quartic interactions whose commutative limit coincides with the usual $\phi^4$ theory. $\kappa$-Poincar\'e invariance forces the integral involved in the actions to be a twisted trace, thus defining a KMS weight for the noncommutative (C*-)algebra modeling the $\kappa$-Minkowski space. The associated modular group and Tomita modular operator are characterized. In all the field theories, the twist generates different planar one-loop contributions to the 2-point function which are at most UV linearly diverging. Some of these theories are free of UV/IR mixing. In the others, UV/IR mixing shows up in non-planar contributions to the 2-point function as a polynomial singularity at exceptional zero external momenta while staying finite at non-zero external momenta. These results are discussed together with the possibility for the KMS weight relative to the quantum space algebra to trigger the appearance of KMS state on the algebra of observables.

Slepton production at e^+e^- colliders in the complex MSSM: a full one-loop analysis

For the search for scalar leptons in the minimal supersymmetric standard model (MSSM) as well as for future precision analyses of these particles an accurate knowledge of their production and decay properties is mandatory. We evaluate the cross sections for the slepton production at e^+e^- colliders in the MSSM with complex parameters (cMSSM). The evaluation is based on a full one-loop calculation of the production mechanisms e^+e^- rightarrow tilde{l}_{gs} tilde{l}_{gs^{prime }} including soft and hard photon radiation. The dependence of the slepton production cross sections on the relevant cMSSM parameters is analyzed numerically. We find sizable contributions to many production cross sections. They amount to roughly 15% of the tree-level results but can go up to 40% or higher in extreme cases. Also the dependence on complex parameters of the one-loop corrections for the production of charged sleptons was found non-negligible. The full one-loop contributions are thus crucial for physics analyses at a future linear e^+e^- collider such as the ILC or CLIC.

Precise prediction for the Higgs-boson masses in the mu nu SSM

The mu nu mathrm {SSM} is a simple supersymmetric extension of the Standard Model (SM) capable of predicting neutrino physics in agreement with experiment. In this paper we perform the complete one-loop renormalization of the neutral scalar sector of the mu nu mathrm {SSM} with one generation of right-handed neutrinos in a mixed on-shell/{overline{mathrm {DR}}} scheme. The renormalization procedure is discussed in detail, emphasizing conceptual differences to the minimal (MSSM) and next-to-minimal (NMSSM) supersymmetric standard model regarding the field renormalization and the treatment of non-flavor-diagonal soft mass parameters, which have their origin in the breaking of R-parity in the mu nu mathrm {SSM}. We calculate the full one-loop corrections to the neutral scalar masses of the mu nu mathrm {SSM}. The one-loop contributions are supplemented by available MSSM higher-order corrections. We obtain numerical results for a SM-like Higgs boson mass consistent with experimental bounds. We compare our results to predictions in the NMSSM to obtain a measure for the significance of genuine mu nu mathrm {SSM}-like contributions. We only find minor corrections due to the smallness of the neutrino Yukawa couplings, indicating that the Higgs boson mass calculations in the mu nu mathrm {SSM} are at the same level of accuracy as in the NMSSM. Finally we show that the mu nu mathrm {SSM} can accomodate a Higgs boson that could explain an excess of gamma gamma events at sim 96 ,mathrm {GeV} as reported by CMS, as well as the 2,sigma excess of b bar{b} events observed at LEP at a similar mass scale.