In order to address some fundamental questions in neutrino physics a wide, future programme of neutrino oscillation experiments is currently under discussion. Among those, long baseline experiments will play a crucial role in providing information on the value of theta13, the type of neutrino mass ordering and on the value of the CP-violating phase delta, which enters in 3-neutrino oscillations. Here, we consider a beta-beam setup with an intermediate Lorentz factor gamma=450 and a baseline of 1050 km. This could be achieved in Europe with a beta-beam sourced at CERN to a detector located at the Boulby mine in the United Kingdom. We analyse the physics potential of this setup in detail and study two different exposures (1 x 10^{21} and 5 x 10^{21} ions-kton-years). In both cases, we find that the type of neutrino mass hierarchy could be determined at 99% CL, for all values of delta, for sin^2(2 theta13) > 0.03. In the high-exposure scenario, we find that the value of the CP-violating phase delta could be measured with a 99% CL error of ~20 deg if sin^2 (2 theta13) > 10^{-3}, with some sensitivity down to values of sin^2(2 theta13) ~ 10^{-4}. The ability to determine the octant of theta23 is also studied, and good prospects are found for the high-statistics scenario.
The ratio of neutral Higgs field vacuum expectation values, tan beta, is one of the most important parameters to determine in type-II Two-Higgs Doublet Models (2HDM), specifically the Minimal Supersymmetric Standard Model (MSSM). Assuming the energies and integrated luminosity of a future high energy e^+e^- linear collider of sqrt{s}=500, 800, 1000, and 1500 GeV and L=1 ab^{-1} we show that associated t H^+/- production in gamma gamma collisions can be used to make an accurate determination of tan beta for low and high tan beta by precision measurements of the gamma gamma -> H^+/- t + X cross …
The constraints on the value of the CKM phase gamma that may be achieved by prospective measurements of sin(2 beta) and sin(2 beta + gamma) are discussed. Significant constraints require quite small errors, and may depend on assumptions about strong phases. The measurement of sin(2 beta + gamma) combined with other experiments could provide valuable limits on new physics in Bd-Bdbar mixing.
If tan beta is large, supersymmetric QCD corrections can become large, putting naive perturbation theory into doubt. I show how these tan-beta-enhanced corrections can be controlled to all orders in alpha_s tanbeta. The result is shown for the decays H^+ -> t b-bar and b -> s gamma.
The physics potential of beta beams is investigated from low to very high gamma values and it is compared to superbeams and neutrino factories. The gamma factor and the baseline are treated as continuous variables in the optimization of the beta beam, while a fixed mass water Cherenkov detector or a totally active scintillator detector is assumed. We include in our discussion also the gamma dependence of the number of ion decays per year. For low gamma, we find that a beta beam could be a very interesting alternative to a superbeam upgrade, especially if it is operated at the second oscillatio…
We propose to measure the Cabibbo-Kobayashi-Maskawa parameter (2 beta+gamma) using B^0 decays involving several intermediate states, and describe a general formalism that applies to a broad class of decays. The main advantage of this method is that the ratios between the interfering amplitudes can be measured without requiring external input. In addition, discrete ambiguities are resolved.
It has been pointed out by Gronau and Rosner that the angle gamma of the unitarity triangle could be determined by combining future results on B_s and B_d decays to K pi. Here we show that it is important to include in the analysis the information on the phase beta which will be determined in the near future. Omitting this information could lead to an error as large as 8 degrees in gamma.
Two of the most important and pressing questions in cosmology and particle physics are: (1) What is the nature of cold dark matter? and (2) Will near-future experiments on neutrinoless double beta decay be able to ascertain that the neutrino is a Majorana particle, i.e. its own antiparticle? We show that these two seemingly unrelated issues are intimately connected if neutrinos acquire mass only because of their interactions with dark matter.
The slope of the beta function at a fixed point is commonly thought to be RG invariant and to be the critical exponent gamma* that governs the approach of any physical quantity R to its fixed-point limit: R*-R proportional to Q^gamma*. Chyla has shown that this is not quite true. Here we define a proper RG invariant, the "effective exponent" gamma(Q), whose fixed-point limit is the true gamma*.
Perturbative O(alpha_s^2) corrections to BR(B -> Xs gamma) in the BLM approximation receive contributions from two-, three- and four-body final states. While all the two-body results are well established by now, the other ones have remained incomplete for several years. Here, we calculate the last contribution that has been missing to date, namely the one originating from interference of the current-current and gluonic dipole operators (K_18^{(2)beta_0} and K_{28}^{(2)beta_0}). Moreover, we confirm all the previously known results for BLM corrections to the photon energy spectrum that involve …
The charged-Higgs contributions to the decay \bar{B} -> X_s gamma are discussed in the minimal supersymmetric standard model at large tan beta. These contributions receive two-loop O(alpha_s tan beta) corrections by squark-gluino subloops, which are nondecoupling in the limit of heavy superpartners and possibly large. Their leading parts are already known and were evaluated by using an effective two-Higgs-doublet Lagrangian. Subleading corrections coming from higher-dimension operators in the effective Lagrangian were ignored, although this is not, a priori, justified when m_{H^\pm} is not muc…
The charged-Higgs boson contributions to the Wilson coefficients C_7 and C_8, relevant for the decay B -> X_s gamma, are discussed in supersymmetric models at large tan beta. These contributions receive two-loop O(alpha_s tan beta) corrections by squark-gluino subloops, which are possibly large and nondecoupling in the limit of heavy superpartners. In previous studies, the relevant two-loop Feynman integrals were approximated by using an effective two-Higgs-doublet lagrangian. However, this approximation is theoretically justified only when the typical supersymmetric scale M_SUSY is sufficient…
Taking the established nonzero value of $θ_{13}$, we study the possibility of extracting the Dirac CP-violating phase by a beta beam facility with a boost factor $100<γ<450$. We compare the performance of different setups with different baselines, boost factors and detector technologies. We find that an antineutrino beam from $^6$He decay with a baseline of $L=1300$ km has a very promising CP discovery potential using a 500 kton Water Cherenkov (WC) detector. Fortunately this baseline corresponds to the distance between FermiLAB to Sanford underground research facility in South Dakota.
Realistic predictions are made for the rates of lepton flavour violating Higgs boson decays, tau --> mu gamma, mu --> e gamma, Bs --> mu+mu-, Bs --> tau mu and tau --> 3mu, via a top-down analysis of the Minimal Supersymmetric Standard Model(MSSM) constrained by SU(5) unification with right-handed Neutrinos and large tan beta. The third family neutrino Yukawa coupling is chosen to be of order 1, in this way our model bares a significant resemblance to supersymmetric SO(10). In this framework the large PMNS mixings result in potentially large lepton flavour violation. Our analysis predicts tau …
In the context of the Grand Unified MSSM, we investigate the fermion mass matrices at GUT scale. We note that from the experimental mass pattern the determinants of the Yukawa matrices at this scale can be unified with good precision. Taking the unification o determinants as an hypothesis, it gives two model independent predictions that in the MSSM turns out to determine an appropriate value for the product m_d m_s and tan(beta)~7-10 in the favored range. We then review a predictive model of SU(3) flavour in the context of supersymmetric SO(10) that nicely implements this mechanism, while expl…
New limits on the Higgs mass from LEP and new calculations on the radiative (penguin) decay of the b->s gamma branching ratio restrict the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM). We find that for the low tan(beta) scenario only one sign of the Higgs mixing parameter is allowed, while the high tan(beta scenario is practically excluded, if one requires all sparticles to be below 1 TeV and imposes radiative electroweak symmetry breaking as well as gauge and Yukawa coupling unification. For squarks between 1 and 2 TeV high tan(beta) scenarios are allowed. …
One of the most troublesome contributions to the NNLO QCD corrections to B -> X_s gamma originates from three-loop matrix elements of four-quark operators. A part of this contribution that is proportional to the QCD beta-function coefficient beta_0 was found in 2003 as an expansion in m_c/m_b. In the present paper, we evaluate the asymptotic behaviour of the complete contribution for m_c >> m_b/2. The asymptotic form of the beta_0-part matches the small-m_c expansion very well at the threshold m_c = m_b/2. For the remaining part, we perform an interpolation down to the measured value of m_c, a…
Realistic predictions are made for lepton flavour violating and flavour changing neutral current decays in the large tan beta regime of a SUSY-seesaw model. Lepton flavour violating neutral Higgs decays are discussed within this framework along with the highly constraining charged lepton decays l_i --> l_j + gamma. In the b-s system the important constraint from b --> s + gamma is studied in conjunction with the rare FCNC Bs --> mu mu (tau mu) decays and the recently measured Delta Ms.
We present a MSSM study of the b -> s gamma decay in a Minimal Flavor Violating (MFV) framework, where the form of the soft SUSY breaking terms is determined by the Standard Model Yukawa couplings. In particular, we address the role of gluino contributions, which are set to zero in most studies of the MFV MSSM. Gluino contributions can play an important role in the MFV MSSM whenever mu * tan(beta) is large. In fact, similarly to chargino contributions, gluino contributions are tan(beta) enhanced and can easily dominate charged Higgs contributions for large values of tan(beta). Even though each…
We study the performance of gamma = 100 Beta-Beam setups based on the decays of 8B and 8Li as a function of the achievable production fluxes and compare them with the standard setups based on 18Ne and 6He decays. For the standard setup we also investigate the physics potential for reduced 18Ne fluxes, since it seems experimentally challenging to achieve the baseline numbers. We find that, contrary to the standard setup, setups based in 8B and 8Li can be sensitive to the mass hierarchy down to values of sin^2 2theta_{13} > 10^-2 by themselves, due to the stronger matter effects granted by the h…
The one-loop branching ratios for the process Z->h(A)+gamma are calculated in the general Two Higgs Doublet Model (Model II) taking into account existing constraints on the model parameters. For Higgs boson masses below 50 GeV and tan beta of order 1-10 the fraction of such Z decays are at the level of 10^{-7}, but can be significantly stronger for very low or high tan beta, where the dependence of these results on other model parameters like sin(beta-alpha) and the mass of the charged Higgs boson is found to be of little importance. The results are compared to the LEP measurements, which are …
The MSSM with large tan(beta) and heavy squarks is a theoretically well motivated and phenomenologically interesting extension of the SM. This scenario naturally accommodates the (g-2)_μanomaly and the upper bound on the Higgs boson mass. In a wide region of the parameter space, visible non-standard effects are expected in a few low-energy observables, such as BR(B->tau nu), BR(B->l+ l-), BR(B->Xs gamma), and BR(mu->e gamma). We analyse the correlations of these non-standard effects under the additional assumption that the relic density of a Bino-like LSP accommodates the observed dark matter …
I review the prospects for the detection of Delta L=2 processes at future colliders. Except in contrived models, the process e- e- -> W- W- is unobservable at future linear colliders unless $\sqrt{s} \gsim 2$ TeV, due to constraints from neutrinoless double beta decay. As there are no analogous constraints on the Majorana mass of the $ν_μ$, mu- mu- -> W- W- could be observed at a muon collider with considerably lower $\sqrt{s}$. One can also consider esoteric processes such as gamma gamma -> mu+ mu+ W- W-. Such processes may be observable if $\sqrt{s} \gsim 4$ TeV.
We explore naturalness constraints on the masses of the heavy Higgs bosons H^0, H^+/-, and A^0 in supersymmetric theories. We show that, in any extension of MSSM which accommodates the 125 GeV Higgs at the tree level, one can derive an upper bound on the SUSY Higgs masses from naturalness considerations. As is well-known for the MSSM, these bounds become weak at large tan beta. However, we show that measurements of b to s gamma together with naturalness arguments lead to an upper bound on tan beta, strengthening the naturalness case for heavy Higgs states near the TeV scale. The precise bound …
The process gamma gamma \to mu tau b bbar is studied in the minimal supersymmetric standard model within a large tan_beta scenario imposing on the parameter space present direct and indirect constraints from B physics and rare LFV tau-decays. At a photon collider based on an e+e- linear collider with a center of mass energy of 800 GeV with the parameters of the TESLA proposal (expected integrated gamma-gamma luminosity L=200-500 inverse fb) the LFV signal can be probed for masses of the heavy neutral Higgs bosons A,H from 300 GeV up to the kinematical limit ~ 600 GeV for tan_beta in the range …
The current experimental determination of the absolute values of the CKM elements indicates that 2|Vub / Vcb/ Vus| = (1-z) with z given by z = 0.19 +(-) 0.14. This fact implies that irrespective of the form of the quark Yukawa matrices, the measured value of the SM CP phase beta is approximately the maximum allowed by the measured absolute values of the CKM elements. This is beta = pi/6 - z/sqrt{3} for gamma = pi/3 + z/sqrt{3}, which implies alpha = pi/2. Alternatively, assuming that beta is exactly maximal and using the experimental measurement, sin(2beta) = 0.726 +(-) 0.037, the phase gamma …
Among the O(alpha_s tan beta) contributions to the Wilson coefficients C_7 and C_8, relevant for the decay bar{B} -> X_s gamma, those induced by two-loop diagrams with charged-Higgs-boson exchange and squark-gluino corrections are calculated in supersymmetric models at large tan beta. The calculation of the corresponding Feynman integrals is exact, unlike in previous studies that are valid when the typical supersymmetric scale M_SUSY is sufficiently larger than the electroweak scale m_weak (\sim m_W, m_t) and the mass of the charged Higgs boson m_{H^\pm}. Therefore, the results presented here …
We discuss possible large contributions to B -> X_s gamma, which can occur at the next-to-leading order in supersymmetric models. They can originate from terms enhanced by tan(beta) factors, when the ratio between the two Higgs vacuum expectation values is large, or by logarithm of M_{susy}/M_W, when the supersymmetric particles are considerably heavier than the W boson. We give compact formulae which include all potentially large higher-order contributions. We find that tan(beta) terms at the next-to-leading order do not only appear from the Hall-Rattazzi-Sarid effect (the modified relation b…
We have studied double Higgs production at future linear colliders while paying special attention to the option of high-energy and high-luminosity photon beams. The main purpose was to examine the feasibility of e+e-, e-gamma and gamma-gamma colliders in order to probe the anomalous triple Higgs coupling, which is crucial for understanding the Standard Model. We considered mainly the cases of light and intermediate Higgs bosons. Double Higgs production is almost background free, except in the MH=MZ mass range, which is discussed separately. It is shown that for a light Higgs boson the HHH coup…
Physics beyond the standard model of electroweak interactions that violates lepton number will, in general, induce operators involving the quark and lepton fields that violate lepton number. I point out that some matrix elements of particular operators are known. In the limit of exact SU(3) flavor symmetry the operator overline{u} gamma_mu (1-gamma_5)d overline{u} gamma_mu (1-gamma_5)d is part of the ${\bf 27}$ representation responsible for Delta I=3/2 strangeness changing decays in the standard model. At leading order in the chiral expansion there is only one coupling constant that describes…
We discuss the minimum requirements for a neutrino beta beam if theta_13 is discovered by an upcoming reactor experiment, such as Double Chooz or Daya Bay. We require that both neutrino mass hierarchy and leptonic CP violation can be measured to competitive precisions with a single-baseline experiment in the entire remaining theta_13 range. We find that for very high isotope production rates, such as they might be possible using a production ring, a (B,Li) beta beam with a gamma as low as 60 could already be sufficient to perform all of these measurements. If only the often used nominal source…
