Scale Of New Physics Research Articles

Lepton-flavored dark matter

In this work, we address two paradoxes. The first is that the measured dark-matter relic density can be satisfied with new physics at O(100 GeV–1 TeV), while the null results from direct-detection experiments place lower bounds of O(10 TeV) on a new-physics scale. The second puzzle is that the severe suppression of lepton-flavor-violating processes involving electrons, e.g. μ→3e, τ→eμμ, etc., implies that generic new-physics contributions to lepton interactions cannot exist below O(10–100 TeV), whereas the 3.6σ deviation of the muon g−2 from the standard model can be explained by a new-physics scale <O(1 TeV). Here, we suggest that it may not be a coincidence that both the muon g−2 and the relic density can be satisfied by a new-physics scale ≲1 TeV. We consider the possibility of a gauged lepton-flavor interaction that couples at tree level only to μ- and τ-flavored leptons and the dark sector. Dark matter thus interacts appreciably only with particles of μ and τ flavor at tree level and has loop-suppressed couplings to quarks and electrons. Remarkably, if such a gauged flavor interaction exists at a scale O(100 GeV–1 TeV), it allows for a consistent phenomenological framework, compatible with the muon g−2, the relic density, direct detection, indirect detection, charged-lepton decays, neutrino trident production, and results from hadron and e+e− colliders. We suggest experimental tests for these ideas at colliders and for low-energy observables.

The Higgs mass and the scale of new physics

In view of the measured Higgs mass of 125 GeV, the perturbative renormalization group evolution of the Standard Model suggests that our Higgs vacuum might not be stable. We connect the usual perturbative approach and the functional renormalization group which allows for a straightforward inclusion of higher-dimensional operators in the presence of an ultraviolet cutoff. In the latter framework we study vacuum stability in the presence of higher-dimensional operators. We find that their presence can have a sizable influence on the maximum ultraviolet scale of the Standard Model and the existence of instabilities. Finally, we discuss how such operators can be generated in specific models and study the relation between the instability scale of the potential and the scale of new physics required to avoid instabilities.

Why should we care about the top quark Yukawa coupling?

In the cosmological context, for the Standard Model to be valid up to the scale of inflation, the top quark Yukawa coupling $y_t$ should not exceed the critical value $y_t^{crit}$, coinciding with good precision (about 0.02%) with the requirement of the stability of the electroweak vacuum. So, the exact measurements of $y_t$ may give an insight on the possible existence and the energy scale of new physics above 100 GeV, which is extremely sensitive to $y_t$. We overview the most recent theoretical computations of $y_t^{crit}$ and the experimental measurements of $y_t$. Within the theoretical and experimental uncertainties in $y_t$ the required scale of new physics varies from $10^7$ GeV to the Planck scale, urging for precise determination of the top quark Yukawa coupling.

Constrained S ^ min $$ \sqrt{{\widehat{S}}_{\min }} $$ and reconstructing with semi-invisible production at hadron colliders

Mass variable \sqrt{\hat{S}_{min}} and its variants were constructed by minimising the parton level center of mass energy that is consistent with all inclusive measurements. They were proposed to have the ability to measure mass scale of new physics in a fully model independent way. In this work we relax the criteria by assuming the availability of partial informations of new physics events and thus constraining this mass variable even further. Starting with two different classes of production topology, i.e. antler and non-antler, we demonstrate the usefulness of these variables to constrain the unknown masses. This discussion is illustrated with different examples, from the standard model Higgs production and beyond standard model resonance productions leading to semi-invisible production. We also utilise these constrains to reconstruct the semi-invisible events with the momenta of invisible particles and thus improving the measurements to reveal the properties of new physics.

Simultaneous explanation of the RK and R(D(⁎)) puzzles

At present, there are several hints of lepton flavor non-universality. The LHCb Collaboration has measured RK≡B(B+→K+μ+μ−)/B(B+→K+e+e−), and the BaBar Collaboration has measured R(D(⁎))≡B(B¯→D(⁎)+τ−ν¯τ)/B(B¯→D(⁎)+ℓ−ν¯ℓ) (ℓ=e,μ). In all cases, the experimental results differ from the standard model predictions by 2–3σ. Recently, an explanation of the RK puzzle was proposed in which new physics (NP) generates a neutral-current operator involving only third-generation particles. Now, assuming the scale of NP is much larger than the weak scale, this NP operator must be made invariant under the full SU(3)C×SU(2)L×U(1)Y gauge group. In this Letter, we note that, when this is done, a new charged-current operator can appear, and this can explain the R(D(⁎)) puzzle. A more precise measurement of the double ratio R(D)/R(D⁎) can rule out this model.

Probing the scale of New Physics at the LHC: The example of Higgs data

We present a technique to determine the scale of New Physics (NP) compatible with any set of data, relying on well-defined credibility intervals. Our approach relies on the statistical view of the effective field theory capturing New Physics at low energy. We introduce formally the notion of testable NP and show that it ensures integrability of the posterior distribution. We apply our method to the Standard Model Higgs sector in light of recent LHC data, considering two generic scenarios. In the scenario of democratic higher-dimensional operators generated at one-loop, we find the testable NP scale to lie within [10,260] TeV at 95% Bayesian credibility level. In the scenario of loop-suppressed field strength-Higgs operators, the testable NP scale is within [28,1200] TeV at 95% Bayesian credibility level. More specific UV models are necessary to allow lower values of the NP scale.

Scaling and tuning of EW and Higgs observables

We study deformations of the SM via higher dimensional operators. In particular, we explicitly calculate the one-loop anomalous dimension matrix for 13 bosonic dimension-6 operators relevant for electroweak and Higgs physics. These scaling equations allow us to derive RG-induced bounds, stronger than the direct constraints, on a universal shift of the Higgs couplings and some anomalous triple gauge couplings by assuming no tuning at the scale of new physics, i.e. by requiring that their individual contributions to the running of other severely constrained observables, like the electroweak oblique parameters or $\Gamma(h \rightarrow \gamma\gamma)$, do not exceed their experimental direct bounds. We also study operators involving the Higgs and gluon fields.

Future sensitivity to new physics inBd,Bs, andKmixings

We estimate, in a large class of scenarios, the sensitivity to new physics in B_d and B_s mixings achievable with 50 ab-1 of Belle II and 50 fb-1 of LHCb data. We find that current limits on new physics contributions in both B_{d,s} systems can be improved by a factor of ~5 for all values of the CP violating phases, corresponding to over a factor of 2 increase in the scale of new physics probed. Assuming the same suppressions by CKM matrix elements as those of the standard model box diagrams, the scale probed will be about 20 TeV for tree-level new physics contributions, and about 2 TeV for new physics arising at one-loop. We also explore the future sensitivity to new physics in K mixing. Implications for generic new physics and for various specific scenarios, such as minimal flavor violation, light third-generation dominated flavor violation, or U(2) flavor models are studied.

Lepton number and flavour violation in TeV-scale left-right symmetric theories with large left-right mixing

The various diagrams leading to neutrinoless double beta decay in the left-right symmetric model have different relative magnitudes, depending on the scale of new physics. Neutrinos acquire mass from both type I and/or type II seesaw terms, making an unambiguous analysis difficult. We study the half-life for double beta decay in the case of type II and type I dominance, in the former case including interference terms. If the heavy neutrinos of the type I seesaw model are at the TeV scale, certain processes can be enhanced. In particular, there are regions of parameter space in which the so-called lambda- and eta-diagrams can give sizable contributions to the half-life for the decay. We perform a detailed study of one such scenario, paying careful attention to constraints from lepton flavour violation.

Standard Model updates and new physics analysis with the Unitarity Triangle fit

We present the summer 2012 update of the Unitarity Triangle (UT) analysis performed by the UTfit Collaboration within the Standard Model (SM) and beyond. The increased accuracy on several of the fundamental constraints is now enhancing some of the tensions amongst and within the constraint themselves. In particular, the long standing tension between exclusive and inclusive determinations of the Vub and Vcb CKM matrix elements is now playing a major role. Then we present the generalisation the UT analysis to investigate new physics (NP) effects, updating the constraints on NP contributions to ΔF=2 processes. In the NP analysis, both CKM and NP parameters are fitted simultaneously to obtain the possible NP effects in any specific sector. Finally, based on the NP constraints, we derive upper bounds on the coefficients of the most general ΔF=2 effective Hamiltonian. These upper bounds can be translated into lower bounds on the scale of NP that contributes to these low-energy effective interactions.

Higgs diphoton rate enhancement from supersymmetric physics beyond the MSSM

We show that supersymmetric ``new physics'' beyond the minimal supersymmetric standard model can naturally accommodate a Higgs mass near 126 GeV and enhance the signal rate in the $h\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ channel, while the signal rates in all the other Higgs decay channels coincide with Standard Model expectations, except possibly the $h\ensuremath{\rightarrow}Z\ensuremath{\gamma}$ channel. The new physics that corrects the relevant Higgs couplings can be captured by two supersymmetric effective operators. We provide a simple example of an underlying model in which these operators are simultaneously generated. The scale of new physics that generates these operators can be around 5 TeV or larger, and outside the reach of the LHC.

Leptonic-Decay-Constant RatiofK+/fπ+from Lattice QCD with Physical Light Quarks

A calculation of the ratio of leptonic decay constants f(K+)/f(π+) makes possible a precise determination of the ratio of Cabibbo-Kobayashi-Maskawa (CKM) matrix elements |V(us)|/|V(ud)| in the standard model, and places a stringent constraint on the scale of new physics that would lead to deviations from unitarity in the first row of the CKM matrix. We compute f(K+)/f(π+) numerically in unquenched lattice QCD using gauge-field ensembles recently generated that include four flavors of dynamical quarks: up, down, strange, and charm. We analyze data at four lattice spacings a ≈ 0.06, 0.09, 0.12, and 0.15 fm with simulated pion masses down to the physical value 135 MeV. We obtain f(K+)/f(π+) = 1.1947(26)(37), where the errors are statistical and total systematic, respectively. This is our first physics result from our N(f) = 2+1+1 ensembles, and the first calculation of f(K+)/f(π+) from lattice-QCD simulations at the physical point. Our result is the most precise lattice-QCD determination of f(K+)/f(π+), with an error comparable to the current world average. When combined with experimental measurements of the leptonic branching fractions, it leads to a precise determination of |V(us)|/|V(ud)| = 0.2309(9)(4) where the errors are theoretical and experimental, respectively.

Origin of neutrino masses at the LHC:ΔL=2effective operators and their ultraviolet completions

Neutrino masses and mixings can be generated in many different ways, with some of these scenarios featuring new physics at energy scales relevant for Large Hadron Collider searches. A systematic approach to constructing a large class of models for Majorana neutrinos may be founded upon a list of gauge-invariant effective operators---formed from quarks, leptons and the Higgs doublet---that violate lepton-number conservation by two units. By opening up these operators in all possible ways consistent with some minimality assumptions, a complete catalog of a class of minimal radiative neutrino mass models may be produced. In this paper we present an analysis of Feynman diagram topologies relevant for the ultraviolet completions of these effective operators and collect these into a simple recipe that can be used to generate radiative neutrino mass models. Since high mass-dimension effective operators are suppressed by powers of the scale of new physics, many of the resulting models can be meaningfully tested at the Large Hadron Collider.

Emergence of the electroweak scale through the Higgs portal

Having discovered a candidate for the final piece of the Standard Model, the Higgs boson, the question remains why its vacuum expectation value and its mass are so much smaller than the Planck scale (or any other high scale of new physics). One elegant solution was provided by Coleman and Weinberg, where all mass scales are generated from dimensionless coupling constants via dimensional transmutation. However, the original Coleman-Weinberg scenario predicts a Higgs mass which is too light; it is parametrically suppressed compared to the mass of the vectors bosons, and hence is much lighter than the observed value. In this paper we argue that a mass scale, generated via the Coleman-Weinberg mechanism in a hidden sector and then transmitted to the Standard Model through a Higgs portal, can naturally explain the smallness of the electroweak scale compared to the UV cutoff scale, and at the same time be consistent with the observed value. We analyse the phenomenology of such a model in the context of present and future colliders and low energy measurements.

Next-to-leading order predictions for dark matter production at hadron colliders

We provide next-to-leading order (NLO) predictions for dark matter (DM) production in association with either a jet or a photon at hadron colliders. In particular we study the production of a pair of fermionic DM particles through a mediator which couples to Standard Model via either a vector, axial-vector, scalar, pseudo-scalar, or gluon-induced coupling. Experimental constraints on the scale of new physics associated with these operators are limited by systematics, highlighting the need for NLO signal modeling. We factorize the NLO QCD and the DM parts of the calculation, allowing the possibility of using the results presented here for a large variety of searches in monojet and monophoton final states. Our results are implemented into the Monte Carlo program MCFM.

Signatures of very high energy physics in the squeezed limit of the bispectrum

We investigate the signatures in the squeezedlimit of the primordial scalar bispectrum due tomodifications of the standard theory at high energy. In particular, weconsider the cases of modified dispersion relations and/or modified initialquantum state (both in the Boundary Effective Field Theory and in theNew Physics Hyper-Surface formulations). Using the in-in formalism we study in detailsthe squeezed limit of the contributions to the bispectrum from allpossible cubic couplings in the effective theory of single-field inflation.We find general features such as enhancements and/or non-local shape of the non-Gaussianities, which are relevant, for example, formeasurements of the halo bias and which distinguish these scenarios from thestandard one (with Bunch-Davies vacuum as initial state and standardkinetic terms). We find that the signatures change according to the magnitude of the scale of new physics, and therefore severalpieces of information regarding high energy physics could be obtainedin case of detection of these signals, especially bounds on the scales of new physics.

Probing lepton gluonic couplings at the LHC

In an effective Lagrangian description of physics beyond the standard model, gluonic couplings of leptons that respect the symmetries of the standard model occur in operators of dimension eight. Normally the effect of such operators is much suppressed in processes that occur at energies below the scale of new physics. For this reason usual studies of the effective Lagrangian are limited to the lowest dimension operators which is typically six. We point out that the large parton luminosity for gluon–gluon interactions at the LHC places these gluonic couplings to leptons within observable reach for a new physics scale near one TeV.

A REVIEW OF NATURALNESS AND DARK MATTER PREDICTION FOR THE HIGGS MASS IN MSSM AND BEYOND

Within a two-loop leading-log approximation, we review the prediction for the lightest Higgs mass (mh) in the framework of constrained MSSM (CMSSM), derived from the naturalness requirement of minimal fine-tuning (Δ) of the electroweak scale, and dark matter consistency. As a result, the Higgs mass is predicted to be just above the LEP2 bound, mh = 115.9±2 GeV , corresponding to a minimal Δ = 17.8, the value obtained from consistency with electroweak and WMAP (3σ) constraints, but without the LEP2 bound. Due to quantum corrections (largely QCD ones for mh above LEP2 bound), Δ grows ≈ exponentially on either side of the above value of mh, which stresses the relevance of this prediction. A value mh&gt;121 (126) GeV cannot be accommodated within the CMSSM unless one accepts a fine-tuning cost worse than Δ&gt;100 (1000), respectively. We review how the above prediction for mh and Δ changes under the addition of new physics beyond the MSSM Higgs sector, parametrized by effective operators of dimensions d = 5 and d = 6. For d = 5 operators, one can obtain values mh as large as 130 GeV with an acceptable Δ&lt;10. The size of the supersymmetric correction that each individual operator of d = 6 brings to the value of mh for points with Δ&lt;100 (&lt;200), is found to be small, of few ≤4 GeV (≤6 GeV) respectively, for M = 8 TeV where M is the scale of new physics. This value decreases (increases) by approximately 1 GeV for a 1 TeV increase (decrease) of the scale M. The relation of these results to the Atlas/CMS supersymmetry exclusion limits is presented together with their impact for the CMSSM regions of lowest fine-tuning.

Detector-related backgrounds in the Karlsruhe Tritium Neutrino Experiment

The Karlsruhe Tritium Neutrino Experiment, or KATRIN, is a next generation tritium beta decay experiment to directly measure neutrino mass with an expected sensitivity of 0.2 eV [KATRIN Design Report 2004 see http://www-ik.fzk.de/~katrin/ ]. Neutrino mass does not fit into the Standard Model, and determining this mass may set the scale of new physics. To achieve this level of sensitivity, backgrounds in the experiment must be minimized. A complete Geant4 [Agostinelli S et al. 2003 Nuclear Instr. Methods A 506 250-303 Allison J et al. 2006 IEEE Transactions on Nuclear Science 53 No. 1 270-8] simulation of KATRINʼs focal plane detector and surrounding region is being developed. These simulations will help guide the design and selection of shielding and detector construction materials to reduce backgrounds from cosmic rays and natural radioactivity.

Probing top anomalous couplings at the Tevatron and the Large Hadron Collider

Chromomagnetic and chromoelectric dipole interactions of the top quark are studied in a model independent framework. Limits are set on the scale of new physics that might lead to such contributions using available Tevatron data. Prospects at the LHC are reviewed.