Kfir Blum

On a possible large width 750 GeV diphoton resonance at ATLAS and CMS

A bstractThe ATLAS and CMS experiments at the LHC have reported an excess of diphoton events with invariant mass around 750 GeV, with local significance of about 3.6 σ and 2.6 σ, respectively. We entertain the possibility that this excess is due to new physics, in which case the data suggest a new particle with 13 TeV LHC production cross section times diphoton branching ratio of about 5 fb. Interestingly, ATLAS reports a mild preference for a sizeable width for the signal of about 45 GeV; this result appears consistent with CMS, and is further supported by improving the compatibility of the 8 TeV and 13 TeV analyses. We focus on the possibility that the new state is a scalar. First, we show that, in addition to the new state that is needed directly to produce the diphoton bump, yet more new particles beyond the Standard Model are needed to induce diphoton decay rate of the right size. Second, we note that if the excess is attributed to the Breit-Wigner peak of a single new state, then the signal strength and width — taken together — suggest a total LHC production cross section of order 105 fb. Restricting to perturbative models without ad-hoc introduction of many new states or exotic charges, we reach the following conclusions: (i) Gluon-fusion cannot explain the required large production cross section. (ii) Tree level production from initial state quarks cannot explain the required branching ratio to two photons. (iii) Tree level production is constrained by flavor data as well as LHC Run-I and Tevatron dijet analyses. Insisting on a large width we are led to suggest that more than one scalar states, nearly degenerate in mass, could conspire to produce an observed wide bump.

Natural SUSY predicts: Higgs couplings

A bstractWe study Higgs production and decays in the context of natural SUSY, allowing for an extended Higgs sector to account for a 125 GeV lightest Higgs boson. Under broad assumptions, Higgs observables at the LHC depend on at most four free parameters with restricted numerical ranges. Two parameters suffice to describe MSSM particle loops. The MSSM loop contribution to the diphoton rate is constrained from above by direct stop and chargino searches and by electroweak precision tests. Naturalness, in particular in demanding that rare B decays remain consistent with experiment without fine-tuned cancellations, provides a lower (upper) bound to the stop contribution to the Higgs-gluon coupling (Higgs mass). Two parameters suffice to describe Higgs mixing, even in the presence of loop induced non-holomorphic Yukawa couplings. Generic classes of MSSM extensions, that address the fine-tuning problem, predict sizable modifications to the effective bottom Yukawa yb. Non-decoupling gauge extensions enhance yb, while a heavy SM singlet reduces yb. A factor of 4–6 enhancement in the diphoton rate at the LHC, compared to the SM prediction, can be accommodated. The ratio of the enhancements in the diphoton vs. the WW and ZZ channels cannot exceed 1.4. The h →

Constraining Dark Matter-Baryon Scattering with Linear Cosmology

b\overline{b}

Combining K0-K0 mixing and D0-D0 mixing to constrain the flavor structure of new physics.

rate in associated production cannot exceed the SM rate by more than 50%.

Beyond MSSM baryogenesis

We derive constraints on elastic scattering between baryons and dark matter using the cosmic microwave background (CMB) data from the Planck satellite and the Lyman-alpha forest data from the Sloan Digital Sky Survey. Elastic scattering allows baryons and dark matter to exchange momentum, affecting the dynamics of linear density perturbations in the early Universe. We derive constraints to scattering cross sections of the form sigma \propto v^n, allowing for a wide range of velocity dependencies with n between -4 and 2. We improve and correct previous estimates where they exist, including velocity-independent cross section as well as dark matter millicharge and electromagnetic dipole moments. Lyman-alpha forest data dominates the constraints for n>-3, where the improvement over CMB data alone can be several orders of magnitude. Dark matter-baryon scattering cannot affect the halo mass function on mass scales M>10^{12} M_{solar}. Our results imply, model-independently, that a baryon in the halo of a galaxy like our own Milky Way, does not scatter from dark matter particles during the age of the galaxy.

Vacuum (meta)stability beyond the MSSM

New physics at high energy scale often contributes to K0-K0 and D0-D0 mixings in an approximately SU(2)L invariant way. In such a case, the combination of measurements in these two systems is particularly powerful. The resulting constraints can be expressed in terms of misalignments and flavor splittings.

AMS-02 Results Support the Secondary Origin of Cosmic Ray Positrons

Taking the MSSM as an effective low-energy theory, with a cutoff scale of a few TeV can make significant modifications to the predictions concerning the Higgs and stop sectors. We investigate the consequences of such a scenario for electroweak baryogenesis. We find that the window for MSSM baryogenesis is extended and, most important, can be made significantly more natural. Specifically, it is possible to have one stop lighter than the top and the other significantly lighter than TeV simultaneously with the Higgs mass above the LEP bound. In addition, various aspects concerning CP violation are affected. Most notably, it is possible to have dynamical phases in the bubble walls at tree level, providing CP violating sources for standard model fermions.

2 Higgs or not 2 Higgs

We study the stability of the Higgs potential in the framework of the effective Lagrangian beyond the minimal supersymmetric standard model (MSSM). While the leading nonrenormalizable operators can shift the Higgs boson mass above the experimental bound, they also tend to render the scalar potential unbounded from below. The destabilization is correlated with the Higgs mass increase, so that if quantum corrections are small the problem is severe. We show that a supersymmetric subleading correction stabilizes the potential within the domain of validity of the effective theory. Constraints on MSSM parameters as well as on higher dimensional operators are derived, ensuring that our vacuum has a lifetime longer than the present age of the Universe. In addition we show that when effective operators are responsible for evading the LEP bound, stability constraints imply an upper bound on the scale of new physics in the few TeV range.

Implications of the CDF tt¯ forward–backward asymmetry for boosted top physics

We show that the recent AMS-02 positron fraction measurement is consistent with a secondary origin for positrons and does not require additional primary sources such as pulsars or dark matter. The measured positron fraction at high energy saturates the previously predicted upper bound for secondary production, obtained by neglecting radiative losses. This coincidence, which will be further tested by upcoming AMS-02 data at higher energy, is a compelling indication for a secondary source. Within the secondary model, the AMS-02 data imply a cosmic ray propagation time in the Galaxy of <10(6) yr and an average traversed interstellar matter density of ~1 cm(-3), comparable to the density of the Milky Way gaseous disk, at a rigidity of 300 GV.

Scalar-mediated \( t\bar{t} \) forward-backward asymmetry

Abstract Motivated by recent results from the LHC experiments, we analyze Higgs couplings in two Higgs doublet models with an approximate PQ symmetry. Models of this kind can naturally accommodate sizable modifications to Higgs decay patterns while leaving production at hadron colliders untouched. Near the decoupling limit, we integrate out the heavy doublet to obtain the effective couplings of the SM-like Higgs and express these couplings in a physically transparent way, keeping all orders in ( m h / m H ) for small PQ breaking. Considering supersymmetric models, we show that the effects on the Higgs couplings are considerably constrained.