Perhaps one needs an extra source of CP violation. This is

needed to create required amount of CP asymmetry in early

universe for the explanation of matter antimatter asymmetry

observed today. Note that if in the early universe matter and

anti matter was available in exactly same amount, then they

would have annihilated to photons. We could not have observed

stars and galaxies and so on.

Just after I published this question, an excellent paper came out by Marco Drewes on exactly this topic

How many new particles do we need after the Higgs boson? Marco Drewes. May 12, 2014. arXiv:1405.2931 [hep-ph].

You can find the answer to Biswajoy Brahmachari's question, namely that the heavy right handed neutrinos, which mix with a CP phase, are perfectly able to generate a lepton asymmetry which then turns into a baryon asymmetry via 'Sphalerons'.

The other concern is regarding dark matter. Now we know

that Lambda-CDM model can describe experimental results

from satellite experiments (i) COBE (II) WMAP (III) Planck.

In standard model we do not have a ready made candidate

for dark matter, which is neutral and whose lifetime is comparable

with the lifetime of universe. After Planck experiment we have seen

that there is a considerable amount of dark matter with cannot

be explained by standard model alone. Cosmic Pie chart is attached.

Credit: ESA/PLANCK

Article "Periodic quantum gravity and cosmology" predicts innumerable particles. The particles of standard model are shown to be just the tip of the iceberg. According to this theory, to look for the fundamental building block of the universe is not a very wise thing to do.

@ Vikram

Your point is very important indeed. We know that even though we

work on 4D models, it is not at all unlikely that extra dimensions

may exist. The extra dimensions need not be linear, but they

are periodic. As an example they can be circular with a radius

of compactification so small that experiments have not yet detected it.

In this scenario, fields are functions of both ordinary coordinates (say x)

and compactified coordinates (say y). Then, we can write a field as

field ---> phi(x,y)

This field is a function of a coordinate y, which is periodic. Therefore

we can expand it in a fourier series in y coordinate. Therefore we will

have fourier modes of the form

phi0(x), phi1(x), phi2(x)..... (infinite numbers)

The lowest mode can be identified with a normal particle which we

have seen in the experiment such as the Higgs boson. But higher

fourier modes are heavy. Their masses can be calculated using the

Klein Gordon equation. These heavy modes are signatures of extra

dimensions.

@ Biswajoy

Periodic quantum gravity (PQG) can predict masses of hundreds and thousands of new particles with a single formula having three quantum numbers s (spin), n (radial) and q (polynomial). Keeping a fixed s, every value of n can be associated with between 1 to hundreds of values of q. Unlike classical quantum theory, every combination of n and q for a given s represents an entirely new particle with totally different mass. This is possible at high energy scales. PQG is not a geometrical theory and it does not support space-time dimensions greater than four.

Vikram, Please give me a reference of Periodic quantum gravity.

Where does the periodicity originate ?

Note that after compactification a theory, which was originally

written in extra dimensions, becomes a 4D theory. The difference

from a usual field theory is that it is a 4D theory with an infinite

number of massive states, often called "an infinite tower of states".

Biswajoy, You can go to my contributions on my profile and download this unpublished article. If you have problem write me at [email protected] and I will send you a copy. Periodicity originates in time f=1/T. Time is strictly periodic in nature, not linear. You can certainly look for the extra dimensions if it is fruitful.

Alain:

I tried to answer a related question: What particles remain to be discovered?

I discovered some math (related to quantum isotropic harmonic oscillators) for which some solutions correlate with the 17 known elementary particles. Other solutions correlate with possible elementary particles (including ones for dark matter and dark energy).

Overall, the solutions fall into 7 families. Each solution can be characterized by 3 parameters. One is 2S - 2*spin/(hbar) - even or odd positive integer. Another is m - mass - zero or non-zero. The third is omega - [plus-or-minus]S(S+1).

I note below some comments pertaining to "non-[dark matter plus dark energy]."

* H-family (2S=0, m≠0, omega=0) - Higgs boson. No new particles expected.

* W-family (2S=2, m≠0, omega>0) - Z and W bosons. No new particles expected.

* O-family (2S=2, m≠0, omega0) - Leptons. Possible yet-to-be-found 'siblings of known leptons.'

* Q-family (2S=1, m≠0, omega

Manuel:

A popular representation of elementary particles features 17 boxes. See, for example, http://en.wikipedia.org/wiki/Elementary_particle . Each box features 1 particle. In this representation, distinct antiparticles do not get their own boxes. In some cases (e.g., neutrinos), physics is not settled as to whether the particle is its own antiparticle.

Manuel:

Apologies for any confusion I may be causing. Let's just say that people generally recognize that people have found (as yet) 17 elementary particles and that some of these particles have distinct antiparticles. Sorry that I mentioned the boxes that people use for depicting information.

Alain:

Permit me to reprise (and attach) some aspects of an updated version my attempted research.  Perhaps the work provides a viable candidate for answering the question "what elementary particles remain to be discovered?" or the similar challenge "provide an analog for elementary particles to the periodic table for elements."  (See especially sections 2.7 and 2.8.)

In parts of that work (for example, section 3.4), I try to correlate traditional thoughts about "hypothetical particles that people think might 'explain' various phenomena" with candidate particles in the catalog I present.

* Notably (given part of your question), the particle I catalog as 64G246& may correlate with properties people might attribute to axions.  (My catalog includes at least 1 other particle that could perform axion-like functions, but, presumably, the other particles would correlate with much weaker interactions.)

* Regarding another of your interests, I show candidates for sterile neutrinos.  (These would be dark-matter particles.)

* And, I show are candidates (which would be composite or compound particles, not elementary particles) for primordial black holes and for WIMPs.

Other sections (including in part 3) suggest particle-based answers regarding other phenomena.

Perhaps the above discussion (and other aspects of my work) would not be a candidate for answering the "minimum number of new discoveries" aspect of your question.  But, perhaps, it is a candidate for answering questions relevant for people discussing the following: such "minimum number" questions, particles beyond those the Standard Model currently includes, relevance of the Planck scale, and so forth.

The right answer to this question might be related to the next level of elementarity (preons) rather than the conventional Standard Model with quarks and leptons. Some heuristic motivation for such a picture may follow from the eight fundamental quantum numbers (charges) presently observed. They correspond in fact to the two weak isospin orientations, three types of colors and three species of quark-lepton families. Their basic carriers could be eight fermion preon fields Pi (i = 1,..., 8) being presumably the fundamental octet of some basic metaflavor symmetry SU(8)MF. Remarkably, apart from this pure heuristic argumentation, the local metaflavor SU(8)MF symmetry as a basic grand unified symmetry of the physical world at small distances is indeed advocated by preon model for composite quarks and leptons (more detail can be found in http://inspirehep.net/record/1716204/files/scoap3-fulltext.pdf)