Resummation of scalar correlator in higher spin black hole background

We consider the proposal that predicts holographic duality between certain 2D minimal models at large central charge and Vasiliev 3D higher spin gravity with a single complex field. We compute the scalar correlator in the background of a higher spin black hole at order $\mathcal{O}$ ( α 5 ) in the chemical potential α associated with the spin-3 charge. The calculation is performed at generic values of the symmetry algebra hs[λ] parameter λ and for the scalar in three different representations. We then study the perturbative data in the Bergshoeff-Blencowe-Stelle limit where λ is taken large and discover remarkable regularities. This leads to formulate a conjectured closed formula for the resummation of the various subleading terms at large λ up to the order $\mathcal{O}$ ( α n λ 2 n −3 )

Neutrino and photon lensing by black holes: radiative lens equations and post-Newtonian contributions

We extend a previous phenomenological analysis of photon lensing in an external gravitational background to the case of a massless neutrino, and propose a method to incorporate radiative effects in the classical lens equations of neutrinos and photons. The study is performed for a Schwarzschild metric, generated by a point-like source, and expanded in the Newtonian potential at first order. We use a semiclassical approach, where the perturbative corrections to neutrino scattering, evaluated at one-loop in the Standard Model, are compared with the Einstein formula for the deflection using an impact parameter formulation. For this purpose, we use the renormalized expression of the graviton/fermion/fermion vertex presented in previous studies. We show the agreement between the classical and the semiclassical formulations, for values of the impact parameter b h of the neutrinos of the order of b h ∼ 20, measured in units of the Schwarzschild radius. The analysis is then extended with the inclusion of the post Newtonian corrections in the external gravity field, showing that this extension finds application in the case of the scattering of a neutrino/photon off a primordial black hole. The energy dependence of the deflection, generated by the quantum corrections, is then combined with the standard formulation of the classical lens equations. We illustrate our approach by detailed numerical studies, using as a reference both the thin lens and the Virbhadra-Ellis lens

Electroweak corrections to photon scattering, polarization and lensing in a gravitational background and the near horizon limit

We investigate the semiclassical approach to the lensing of photons in a spherically symmetric gravitational background, starting from Born level and include in our analysis the radiative corrections obtained from the electroweak theory for the graviton/photon/photon vertex. In this approach, the cross section is related to the angular variation of the impact parameter ( b ), which is then solved for b as a function of the angle of deflection, and measured in horizon units ( b h ≡ b/ (2 GM )). Exact numerical solutions for the angular deflection are presented. The numerical analysis shows that perturbation theory in a weak background agrees with the classical Einstein formula for the deflection already at distances of the order of 20 horizon units (∼20 b h ) and it is optimal in the description both of very strong and weak lensings. We show that the electroweak corrections to the cross section are sizeable, becoming very significant for high energy gamma rays. Our analysis covers in energy most of the photon spectrum, from the cosmic microwave background up to very high energy gamma rays, and scatterings with any value of the photon impact parameter. We also study the helicity-flip photon amplitude, which is of O ( α 2 ) in the weak coupling α , and its massless fermion limit, which involves the exchange of a conformal anomaly pole. The corresponding cross section is proportional to the Born level result and brings to a simple renormalization of Einsten’s formula

Vacuum stability in U(1) -prime extensions of the Standard Model with TeV scale right handed neutrinos

We investigate a minimal U(1)′ extension of the Standard Model with one extra complex scalar and generic gauge charge assignments. We use a type-I seesaw mechanism with three heavy right handed neutrinos to illustrate the constraints on the charges, on their mass and on the mixing angle of the two scalars, derived by requiring the vacuum stability of the scalar potential. We focus our study on a scenario which could be accessible at the LHC, by selecting a vacuum expectation value of the extra Higgs in the TeV range and determining the constraints that emerge in the parameter space. To illustrate the generality of the approach, specific gauge choices corresponding to U(1)B−L U(1)R and U(1)χ are separately analyzed. Our results are based on a modified expression of one of the β functions of the quartic couplings of the scalar potential compared to the previous literature. This is due to a change in the coefficient of the Yukawa term of the right handed neutrinos. Differently from previous analysis, we show that this coupling may destabilize the vacuum

Perspectives on a supersymmetric extension of the standard model with a Y = 0 Higgs triplet and a singlet at the LHC

We investigate a supersymmetric extension of the Minimal Supersymmetric Standard Model (MSSM), called the TNMSSM, containing a SU(2) Higgs triplet T ^ $$\left(\widehat{T}\right)$$ of Y = 0 hypercharge and a singlet superfields ( Ŝ ) in the corresponding superpotential. The model can be viewed, equivalently, as an extension of the NMSSM with the addition of a T ^ − S ^ $$\widehat{T}-\widehat{S}$$ interaction and of an extra coupling of the triplet to the two Higgs doublets of the NMSSM. In this scenario the Higgs particle spectrum at tree-level gets additional mass contributions from the triplet and singlet scalar components respect to the MSSM, which are particularly enhanced at low tan β . We calculate the one-loop Higgs masses for the neutral physical Higgs bosons by a Coleman-Weinberg effective potential approach. In particular, we investigate separately the impact of the radiative corrections due to the electroweak, gauge-gaugino-higgsino, fermion-sfermion and Higgs self-interactions to the Higgs masses. Due to the larger number of scalars and of triplet and singlet couplings, the Higgs corrections can be larger than the strong corrections. This reduces the amount of fine-tuning required to fit the recent Higgs data. Using the expressions of the beta-functions of the model, we show that the large triplet singlet coupling remains perturbative up to ∼ 10 8−10 GeV. The model is also characterized by a light pseudoscalar in the spectrum, which is a linear combination of the triplet, doublet and singlet CP-odd components. We discuss the production and decay signatures of the Higgs bosons in this model, including scenarios with hidden Higgses, which could be investigated at the LHC in the current run

Supergravity one-loop corrections on AdS 7 and AdS 3 , higher spins and AdS/CFT

As was shown earlier, the one-loop correction in 10d supergravity on AdS5×S5 corresponds to the contributions to the vacuum energy and 4d boundary conformal anomaly which are minus the values for one N=4 Maxwell supermultiplet, thus reproducing the subleading term in the N2−1 coefficient in the dual SU(N) SYM theory. We perform similar one-loop computations in 11d supergravity on AdS7×S4 and 10d supergravity on AdS3×S3×T4 . In the AdS7 case we find that the corrections to the 6d conformal anomaly a-coefficient and the vacuum energy are again minus the ones for one (2,0) tensor multiplet, suggesting that the total a-anomaly coefficient for the dual (2,0) theory is 4N3−9/4N−7/4 and thus vanishes for N=1 . In the AdS3 case the one-loop correction to the vacuum energy or 2d central charge turns out to be equal to that of one free (4,4) scalar multiplet, i.e. is c=+6 . This reproduces the subleading term in the central charge c=6(Q1Q5+1) of the dual 2d CFT describing decoupling limit of D5–D1 system. We also present the expressions for the 6d a-anomaly coefficient and vacuum energy contributions of general-symmetry higher spin field in AdS7 and consider their application to tests of vectorial AdS/CFT with the boundary conformal 6d theory represented by free scalars, spinors or rank-2 antisymmetric tensors

Higher spins in AdS 5 at one loop: vacuum energy, boundary conformal anomalies and AdS/CFT

We consider general-symmetry higher spin fields in AdS 5 and derive the expressions for their one-loop corrections to vacuum energy E c and the associated 4d boundary conformal anomaly a-coefficient. We propose a similar expression for the second conformal anomaly c-coefficient. We show that all the three quantities ( E c , a , c) computed for N = 8 $$\mathcal{N}=8$$ gauged 5d supergravity are equal to − 1 2 $$-\frac{1}{2}$$ of their values for N = 4 $$\mathcal{N}=4$$ conformal 4d supergravity and also to twice the values for N = 4 $$\mathcal{N}=4$$ Maxwell multiplet. This gives a 5d derivation of the fact that the system of N = 4 $$\mathcal{N}=4$$ conformal supergravity and four N = 4 $$\mathcal{N}=4$$ Maxwell multiplets is anomaly free. The values of ( E c , a , c) for the states at level p of Kaluza-Klein tower of 10d type IIB supergravity compactified on S 5 turn out to be equal to those for p copies of N = 4 $$\mathcal{N}=4$$ Maxwell multiplets. This may be related to the fact that these states appear in the tensor product of p superdoubletons. Under a natural regularization of the sum over p , the full 10d supergravity contribution is then minus that of one Maxwell multiplet, in agreement with the standard adjoint AdS/CFT duality (SU( N ) SYM contribution is N 2 − 1 times that of one Maxwell multiplet). We also verify the matching of ( E c , a , c) for spin 0 and 1 2 $$\frac{1}{2}$$ boundary theory cases of vectorial AdS/CFT duality. The consistency conditions for vectorial AdS/CFT turn out to be equivalent to the cancellation of anomalies in the closely related 4d conformal higher spin theories. In addition, we study novel example of the vectorial AdS/CFT duality when the boundary theory is described by free spin 1 fields and is dual to a particular higher spin theory in AdS 5 containing fields in mixed-symmetry representations. We also discuss its supersymmetric generalizations

Fermion scattering in a gravitational background: electroweak corrections and flavour transitions

We investigate the role of the electroweak corrections to the scattering cross section of Standard Model fermions with gravity. We use both an approach of scattering off an external potential, where the gravitational field is treated as a classical background generated by a heavy source, and the usual interaction based on the one-graviton-exchange. In the potential appoach we consider the fields both of a localized and of a distributed gravitational source of spherical symmetry and uniform density, separating the cases of interactions taking place both in the inner and external regions of the source. This allows to make a distinction between interactions involving neutrinos and dark matter particles with a realistic gravity source, which cover the inner region, and the rest of the Standard model fermions. The role of the gravitationally induced flavour-changing transitions, as well as the flavour diagonal ones, are investigated in the limit of both large and small momentum transfers, deriving the structure of the corresponding Hamiltonian

Conformal a-anomaly of some non-unitary 6d superconformal theories

We compute the conformal anomaly a-coefficient for some non-unitary (higher derivative or non-gauge-invariant) 6d conformal fields and their supermultiplets. We use the method based on a connection between 6d determinants on S 6 and 7d determinants on AdS 7 . We find, in particular, that (1,0) supermultiplet containing 4-derivative gauge-invariant conformal vector has precisely the value of a-anomaly as attributed in arXiv:1506.03807 (on the basis of R-symmetry and gravitational ’t Hooft anomaly matching) to the standard (1,0) vector multiplet. We also show that higher derivative (2,0) 6d conformal supergravity coupled to exactly 26 (2,0) tensor multiplets has vanishing a-anomaly (and also vanishing Casimir energy on 5-sphere). This is the 6d counterpart of the known fact of cancellation of the conformal anomaly in the 4d system of N = 4 $$\mathcal{N}=4$$ conformal supergravity coupled to 4 vector N = 4 $$\mathcal{N}=4$$ multiplets. In the case when 5 of tensor multiplets are chosen to be ghost-like and the conformal symmetry is spontaneously broken by a quadratic scalar constraint the resulting IR theory may be identified with (2,0) Poincaré supergravity coupled to 21 = 26 − 5 tensor multiplets. The latter theory is known to be special — it is gravitational anomaly free and results upon compactification of 10d type IIB supergravity on K3

New Physics signals from measurable polarization asymmetries at LHC

We propose a new type of Z polarization asymmetry in bottom- Z production at LHC that should be realistically measurable and would provide the determination of the so-called <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>A</mi></mrow><mrow><mi>b</mi></mrow></msub></math> parameter, whose available measured value still appears to be in disagreement with the Standard Model prediction; we discuss the overall expected precision of this measurement and its implications. If Supersymmetry is found, a second polarization, i.e. the top longitudinal polarization in top-charged Higgs production, would neatly identify the tan β parameter. In this case, the value of <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>A</mi></mrow><mrow><mi>b</mi></mrow></msub></math> should be in agreement with the Standard Model. If Supersymmetry does not exist, a residual disagreement of <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>A</mi></mrow><mrow><mi>b</mi></mrow></msub></math> from the Standard Model prediction would be a clean signal of New Physics of “non-Supersymmetric” origin