2,113 research outputs found
Chiral heavy fermions in a two Higgs doublet model: 750 GeV resonance or not
We revisit models where a heavy chiral 4th generation doublet of fermions is
embedded in a class of two Higgs doublets models (2HDM) with a discrete
symmetry, which couples the "heavy" scalar doublet only to the 4th generation
fermions and the "light" one to the Standard Model (SM) fermions - the
so-called 4G2HDM introduced by us several years ago. We study the constraints
imposed on the 4G2HDM from direct searches of heavy fermions, from precision
electroweak data (PEWD) and from the measured production and decay signals of
the 125 GeV scalar, which in the 4G2HDM corresponds to the lightest CP-even
scalar h. We then show that the recently reported excess in the
spectrum around 750 GeV can be accommodated by the heavy CP-even scalar of the
4G2HDM, H, resulting in a unique choice of parameter space: negligible mixing
(sin\alpha ~ O(0.001)) between the two CP-even scalars h,H and heavy 4th
generation quark and lepton masses m_t',m_b' < 400 GeV and
> 900 GeV, respectively. Whether or not the 750 GeV \gamma \gamma resonance is
confirmed, interesting phenomenology emerges in q' - Higgs systems (q'=t',b'),
that can be searched for at the LHC. For example, the heavy scalar states of
the model, S=H,A,H^+, may have BR(S -> q'q') ~ O(1), giving rise to observable
q'q' signals on resonance, followed by the flavor changing q' decays t'->uh
(u=u,c) and/or b'->dh (d=d,s,b). This leads to distinct high jet-multiplicity
signatures, with or without charged leptons, of the form q'q' -> (nj + mb +
lW)_S (j and b being light and b-quark jets, respectively), with n+m+l =6-8 and
unique kinematic features. It is also shown that the 4G2HDM can easily
accommodate the interesting recent indications of a percent-level branching
ratio in the lepton-flavor-violating (LFV) decay of the 125
GeV Higgs, if confirmed.Comment: 13 pages, late
A Configurationally-Resolved-Super-Transition-Arrays method for calculation of the spectral absorption coefficient in hot plasmas
A new method, 'Configurationally-Resolved-Super-Transition-Arrays', for
calculation of the spectral absorption coefficient in hot plasmas is presented.
In the new method, the spectrum of each Super-Transition-Array is evaluated as
the Fourier transform of a single Complex Pseudo Partition Function, which
represents the exact analytical sum of the contributions of all constituting
unresolved transition arrays sharing the same set of one-electron solutions.
Thus, in the new method, the spectrum of each Super-Transition-Array is
resolved down to the level of the (unresolved) transition arrays. It is shown
that the corresponding spectrum, evaluated by the traditional
Super-Transition-Arrays (STA) method [A. Bar Shalom, J. Oreg, W.H. Goldstein,
D. Shvarts and A. Zigler, Phys. Rev. A 40, 3183 (1989)], is just the coarse
grained Gaussian approximation of the
Configurationally-Resolved-Super-Transition-Array. A new computer program is
presented, capable of evaluating the absorption coefficient by both the new
configurationally resolved and the traditional Gaussian Super-Transition-Arrays
methods. A numerical example of gold at temperature 1keV and density 0.5
gr/cm^{3}, is presented, demonstrating the simplicity, efficiency and accuracy
of the new method
Proposing "b-Parity" - a New Approximate Quantum Number in Inclusive b-jet Production - as an Efficient Probe of New Flavor Physics
We consider the inclusive reaction \ell^+ \ell^- -> nb +X (n = number of
b-jets) in lepton colliders for which we propose a useful approximately
conserved quantum number b_P=(-1)^n that we call b-Parity (b_P). We make the
observation that the Standard Model (SM) is essentially b_P-even since SM
b_P-violating signals are necessarily CKM suppressed. In contrast new flavor
physics can produce b_P=-1 signals whose only significant SM background is due
to b-jet misidentification. Thus, we show that b-jet counting, which relies
primarily on b-tagging, becomes a very simple and sensitive probe of new flavor
physics (i.e., of b_P-violation).Comment: 5 pages using revtex, 2 figures embadded in the text using epsfig. As
will appear in Phys.Rev.Lett.. Considerable improvement was made in the
background calculation as compared to version 1, by including purity
parameters, QCD effects and 4-jets processe
Efficiency at optimal work from finite reservoirs: a probabilistic perspective
We revisit the classic thermodynamic problem of maximum work extraction from
two arbitrary sized hot and cold reservoirs, modelled as perfect gases.
Assuming ignorance about the extent to which the process has advanced, which
implies an ignorance about the final temperatures, we quantify the prior
information about the process and assign a prior distribution to the unknown
temperature(s). This requires that we also take into account the temperature
values which are regarded to be unphysical in the standard theory, as they lead
to a contradiction with the physical laws. Instead in our formulation, such
values appear to be consistent with the given prior information and hence are
included in the inference. We derive estimates of the efficiency at optimal
work from the expected values of the final temperatures, and show that these
values match with the exact expressions in the limit when any one of the
reservoirs is very large compared to the other. For other relative sizes of the
reservoirs, we suggest a weighting procedure over the estimates from two valid
inference procedures, that generalizes the procedure suggested earlier in [J.
Phys. A: Math. Theor. {\bf 46}, 365002 (2013)]. Thus a mean estimate for
efficiency is obtained which agrees with the optimal performance to a high
accuracy.Comment: 14 pages, 6 figure
Collider signals of a composite Higgs in the Standard Model with four generations
Recent fits of electroweak precision data to the Standard Model (SM) with a
4th sequential family (SM4) point to a possible "three-prong composite
solution": (1) the Higgs mass is at the TeV-scale, (2) the masses of the 4th
family quarks t',b' are of O(500) GeV and (3) the mixing angle between the 4th
and 3rd generation quarks is of the order of the Cabibbo angle, \theta_{34} ~
O(0.1). Such a manifestation of the SM4 is of particular interest as it may
suggest that the Higgs is a composite state, predominantly of the 4th
generation heavy quarks. Motivated by the above, we show that the three-prong
composite solution to the SM4 can have interesting new implications for Higgs
phenomenology. For example, the Higgs can decay to a single heavy 4th
generation quark via the 3-body decays (through an off-shell t' or b') H ->
t'(bar) t'* -> t'(bar) b W+ and H -> b'(bar) b'* -> b'(bar) t W-. These flavor
diagonal decays can be dramatically enhanced at the LHC (by several orders of
magnitudes) due to the large width effects of the resonating heavy Higgs in the
processes gg -> H -> t'(bar) t'* -> t'(bar) b W+ and gg -> H -> b'(bar) b'* ->
b'(bar) t W-, thus yielding a viable signal above the corresponding continuum
QCD production rates. In addition, the Higgs can decay to a single t' and b' in
the loop-generated flavor changing (FC) channels H -> b' b(bar), t' t(bar).
These FC decays are essentially "GIM-free" and can, therefore, have branching
ratios as large as 10^{-4} - 10^{-3}.Comment: As published in Phys.Lett.B688:195-201,201
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